ntsc part i: sync signals and timing troubleshooting the ... … · the professional magazine for...

THE PROFESSIONAL MAGAZINE FOR ELECTRONICS AND COMPUTER SERVICING

Servicing & Technology July 1994/$3.00

NTSC Part I: Sync signals and timing

Troubleshooting the CD laser head assembly

Servicing home office productsA hard disk-drive'Virrher.-----Servicing eltlaritron 15eyriters

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Contents

page 23

FEATURES6 Servicing electronic typewriters

By Dale C. ShackelfordThis article highlights the do's anddon'ts of typewriter repair.

11 A hard disk drive primerBy John RossRoss describes the components ofand details the types of hard diskdrives, provides basic installationtips and lists several references.

17 Removing conformal coatingsBy James L. WitcherThis discussion on conformal coat-ings suggests methods on remov-ing these coatings and how thisremoval can make the repairprocess easier.

20 Electronic servicing for perfor-mance and reduced environmen-tal impactBy Dr. Mo TaziChemicals used in today's servicingare dramatically changing due tostringent environmental regula-tions. Knowing about these chemi-cals will help you make informedchoices in your efforts to conformto these regulations.

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23 Troubleshooting the CD laserhead assemblyBy Homer DavidsonWhen a compact disc player isbrought in for service, the conditionof the laser head assembly maydetermine if the unit is worth repair-ing. The technician can save a lot ofvaluable time and trouble by firstperforming a few quick tests on thelaser head.

28 Tips on using test equipmentprobesBy Vaughn D. MartinThis article provides a number oftips on using test equipment probesbased on information from ES&T'spreviously published "test equip-ment probes" three-part series.

47 NTSC Part I: Sync signals andtimingBy Arthur FlavellThis is the first article in a series ofthree that explores the NTSC videosignal and how it relates to servic-ing of video equipment.

51 Ten important CD waveformsBy Homer DavidsonWhen faced with a malfunctioningCD player, observation of someimportant waveforms in the variouscircuits may help locate a defectivecircuit.

DEPARTMENTS2

3

5

19

33

56

Editorial

News

Literature

Test Your Electronics Knowledge

Profax

What Do You Know AboutElectronics?The "Toss it" syndrome

59 Business CornerPart 10 of the TQM series

60 Video CornerAdditive vs subtractive colors

65 Products

66 Photofacts

67 Troubleshooting Tip

68 Books

69 Classifieds/Readers' Exchange

72 Advertisers' Index

ON THE COVERNews stories recently reported that in1994 more people bought PCs for theirhomes than for business. Add the num-ber of fax machines, copiers and otheroffice products bought for home use andthat represents a sizable base in resi-dences that will eventually require ser-vice. photo courtesy of Fluke)

July 1994 Electronic Servicing & Technology 1

Editorial

Ignoranceis (not) bliss

Sam Wilson called me a few weeksback. It seems that he has received a cou-ple of hundred requests for the capacitorcolor code listing that he offered to sendto readers who requested one. Sam was alittle bit surprised and overwhelmed bythe numbers who requested that informa-tion. I was surprised too, but after a littlereflection, it no longer seemed odd.

For one thing, it occurred to me thatelectronics is an abstruse area of study inwhich many subjects are hidden in vary-ing degrees from its practitioners. Wespeak easily of electrons and electronics,yet no one has ever seen an electron, norwill anyone ever see an electron. Mostaccept on faith the explanations con-ceived by the brilliant minds of electron-ics science and imparted to us by teach-ers, confirmed to some extent by our ownobservations, and then go on.

Unfortunately, the disciplines of elec-tronics, electronic engineering, electron-ics technology and all the related fieldsare very broad, very deep, and denselypopulated with concepts that are difficultto grasp and that are just not discussed ineveryday conversation.

So what we have to deal with in elec-tronics are difficult to understand con-cepts developed by brilliant minds thatoperate on a whole other level than theminds of ordinary mortals, passed downand filtered through the imperfect intelli-gences of professors and instructors, intoour own less than perfect minds.

To make the situation still worse, thereisn't time in any course of study to includeeverything, so teachers pass on an incom-plete as well as imperfect body of knowl-edge to the students. What areas theyemphasize and which areas they short-change depends on what areas the instruc-tor is most competent in, what areas theyare most interested in, and what types ofquestions the students ask.

But that's only the start of the problem.Manufacturers and the engineers whowork for them contribute to the problem.It is not their intention to do so, it justsometimes works out that way.

For example, where do they come upwith their systems of identification ofcomponents? In the case of standard car-bon composition resistors, identificationis not bad. The resistors are marked withcolors and each color stands for a num-ber. Every technician learns the colorcode in his first year of technical school.

Generic discrete semiconductor desig-nations also make sense, for the most part;IN designates a diode, 2N designates atransistor.

Even some capacitor codes make sense,if you know how to interpret them. Theproblem is, some of the capacitor codesare familiar to us, but some capacitorvalue codes, either necessarily because ofthe small size of the capacitor, or usedbecause the capacitor was manufacturedfor a use other than in electronics, leavethe average technician high and dry.

In my conversation with Sam, he men-tioned two examples of this. You mayhave occasionally run across a smallcapacitor that has a number on it. The firsttwo digits designate the value of the com-ponent, and the third number indicates thenumber of zeros to add at the right handside of the number. Then, because all ofthe capacitors so marked are in pico-farads, you multiply by 10-2.

For example, a capacitor marked 103has a value of 10 followed by three zeros,or 10,000 picofarads, or 10,000 x 10-12;or 10 x 103 x 10-12; or 10 x 10-9; or0.001µF.

And here's one that really might throwyou for a loop. You'll occasionally find afairly large capacitor, with the letter M inits value. That M doesn't indicate million,or mega, as electronics technicians arefamiliar with. In this case, the capacitorwas installed in some kind of productordinarily associated with a manufactur-ing plant; say a motor -start capacitor.Those folks are accustomed to using theletter M to designate thousands, that is theRoman numeral M.

The only way to be able to access all ofthis information is to pay close attentionany time you're in a structured class,hoard any materials that you ever get yourhands on that pertains to product identi-fication, and constantly seek out this typeof information when you run across anykind of component that you're not famil-iar with. Good luck.

And, by the way, if you ever run acrossa piece of information that puzzles you,write to me, or to Sam, or one of our otherauthors, in care of ES&T, and we'll tryto find an answer and pass it along to youand to all of our other readers.

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2 Electronic Servicing & Technology July 1994

NewsSmall appliance certification testTechnicians who want to order the

open -book, mail -in test to be certified towork on small appliances (Type I techni-cians) can now do so by calling 1 -800-394 -TEST (8378). Tests cost $22 eachand can be ordered with a VISA or Mas-terCard by calling the 800 number. It isanswered 24 -hours a day, 7 days a week.

Technicians and companies who wishto order by check should mail their pay-ment of $22 per test to: NARDA CFCTest, Suite 310, 10 East 22nd Street, Lom-bard, IL 60148. Those with questionsabout the test or procedures may call thetest administrator at 1-708-953-8956.

This is the test developed by an allianceof the Association of Home ApplianceManufacturers (AHAM) and the NorthAmerican Retail Dealers Association(NARDA) and approved by the Environ-mental Protection Agency (EPA). Thetest package includes a 50 -page compre-hensive study manual, a 50 -question testbooklet, and test answer form. The self -study manual is designed to provide tech-nicians with all of the information aboutrefrigerant recovery and the impact ofrefrigerants on the environment, whichthey need in order to pass the certificationexam. Technicians are able to study thebooklet, answer the 50 test questions attheir convenience and mail back theirquestion and answer forms.

EPA requires that technicians answer21 out of 25 (84%) questions correctly oneach of the two sections of the test in orderto be certified. Twenty-five questions inone section are on general ozone deple-tion, refrigeration topics and EPA regula-tory requirements. The other 25 questionsare Type I specific questions about leakdetection, recovery techniques, safety,shipping and disposal.

Those who pass the test will get a cer-tificate and wallet card indicating thatthey are certified to recover refrigerantfrom small appliances. Retests will beavailable for those who do not pass.

All technicians who service small ap-pliances must be certified by November14, 1994. Small Appliances, as definedby EPA regulations, are any of the follow-ing products that are fully manufactured,charged and hermetically sealed at thefactory with five pounds or less of refrig-

erants: refrigerators and freezers de-signed for home use, room air condition-ers including window air conditionersand packaged terminal air conditioners,packaged terminal heat pumps. dehumid-ifiers, under the counter icemakers, vend-ing machines and drinking water coolers.

Sales of large screen TV and videoproducts increase

The video market exhibited signs ofgathering momentum in February as salesof color televisions 25 -inches and over,TV/VCR combinations, projection TVs,VCR decks, and camcorders rose in themonth, according to statistics released bythe Electronic Industries Association'sConsumer Electronics Group (EIA/CEG).

Big ticket items performed especiallywell in February. Strong increases wereregistered by both large screen direct -view and rear projection televisions, per-haps reflecting retailer confidence in con-sumer attitudes toward home theater. Re-placement and upgrade sales of VCRs,continue to be made-witness the double-digit gain in sales of hi -ti stereo models.

"Since the color TV business is a re-placement market, it is natural that con-sumers are upgrading to bigger screentelevisions," says Jim Palumbo, SeniorVice President Sony Consumer Televi-sion Products Company. "They are recog-nizing that a big screen television is thecenterpiece of a home entertainment sys-tem and family environment, and this isan ideal way to make movies, sports andmusic videos come to life. The continuedgrowth in big -screen televisions rein-forces consumer acceptance of the homeentertainment concept and reflects chang-ing lifestyles."

Sales of color televisions 25 -inches andover rose 16 percent in February over thesame period last year, helping to offset a21 percent decrease in combined sales of20 -inch and 13 -inch and under screensizes. Overall, unit shipments of direct -view color televisions were basically flatin February.

Projection television sales rose at thefastest rate in more than two years, as allscreen size categories tracked postedgains of more than 20 percent. Total salesof projection sets were up 44 percent inFebruary, more than tripling January's 14

percent increase. The bigger the screensize, the better the sales were in February,as evidenced by the 127 percent increaserealized by models 55 -inches and over.

TV/VCR combination units logged an-other solid month in February, rising 35percent. Growth was evenly distributedbetween the 13 -inch and under, and 13 -inch and over categories. Total sales areup 42 percent in the year-to-date.

VCR deck sales posted a three percentgain in February, rebounding from a 10percent decline in January. Sales totaled1.6 million in the first two months of thisyear. Hi-fi stereo models were especiallystrong in February, rising 24 percent. Hi-fi stereo units accounted for over 40 per-cent of total VCR volume in the month,up from the same period last year whenhi-fi stereo models accounted for about31 percent in total volume.

Camcorder sales rose two percent inFebruary, adding to the six percent gainin the year-to-date category. Compactmodels rose seven percent in the month,offsetting an eight percent decline in salesof full-size units. The drop in sales of full-size units, however, was only the secondin the last year.

Second annualServicer Excellence Awards

Nintendo of America Inc. has chosensix World Class Service Centers as recip-ients of the 1993 Service ExcellenceAwards. The service centers demonstrat-ed dedication and superior support toNintendo and consumers in providingafter -the -sale customer service support.

The winning service companies are:

National Winner-Falcon Electronics,Colorado Springs, CO

Northeastern Region-Doctor Video,Christiansburg, VA & United Radio, Inc.,Syracuse, NY

Central Region-Appliance & AudioRepair, St. Charles, MO

Southeastern Region-Bayard Elec-tronics, Dallas, TX

Western Region-Falcon Electronics,Denver, CO

Nintendo maintains a nationwide net-work of nearly 3,000 Field CustomerService Centers to provide consumers


with product maintenance and repair,replacement components, and spareparts. Established in 1990 by Nintendo'sNational Field Service department, thenetwork has grown considerably withlocations across the U.S. and Canada.

Winners were evaluated quarterly ontheir quality of service, turn -around timeof repairs, customer satisfaction levels,and outstanding marketing efforts through-out 1993.

The National Grand Prize winner isawarded four round-trip airline tickets toanywhere in the continental U.S. All win-ners receive an expense -paid four -dayweekend for two to an awards presenta-tion and gala banquet in their honor to beheld March 25-28 in the Seattle, WA area.

"This is a way of recognizing our Inde-pendent Authorized Servicers who pro-vide outstanding support to our consum-ers. More than one out of every threehomes in America has a Nintendo systemtoday," said Jim Rushton, director, Na-tional Field Service. "Nintendo consum-ers can rely on quality support every stepof the way. That means excellent service,even after the product sale."

EIA announces free "hands-on"technical workshops

The Electronic Industries Association(EIA) offers several courses in VCR, dig-ital/microprocessor applications, PC ser-vicing and video laser disc servicing, cov-ering theory and hands-on training. Allworkshops, except video laser are fivedays, 40 hours with an enrollment of 20people; video laser disc is a three-day ses-sion. These courses will be presented incities throughout the United States, dur-ing the current year.

Technician programs are co -sponsoredby local chapters of the National Elec-tronic Service Dealers Association andthe International Society of CertifiedElectronics Technicians (NESDA/ISCET). Five-day workshops for elec-tronics instructors in vocational educa-tion are co -sponsored by state depart-ments of vocational education and localteaching institutions.

The workshops are provided at no costto the attendee by EIA. Anyone interest-ed in attending should contact EIA at

2001 Pennsylvania Avenue, NW, Wash-ington, DC 20006; 202-457-4986.

EIA offers free resident workshopsThe Electronic Industries Association

(EIA) offers workshops on color televi-sion and VCR servicing throughout theyear at five locations. These workshopsare open to consumer electronics techni-cians and educators. While covering ba-sic principles and practical troubleshoot-ing on modern equipment, the courses areparticularly suited for technicians whowish to be updated on their basic theoryand troubleshooting abilities.

Considering the high quality and time-liness of these programs and the materi-als the attendees retain, EIA believes thatthe practical nature of these workshopswill provide the attendees with new skillsof immediate benefit.

These courses have an estimated $500.00value, but EIA/CEG offers them free toqualified technicians. Attendees mustprovide their own transportation andlodgings while at the workshops.

For more information write to: EIA/CEG Product Services, Department 287,Washington, DC 20005. You can call at202-457-4986 or Fax 202-457-4901.

Fiber optic installers conferenceexpands, moves to CA

The next fiber optic (FO) InstallersConference, now called "Fiber U," willbe held July 25-28, 1994 at the SheratonLong Beach, CA.

To help the beginner, the conferencehas added a "novice course," with com-prehensive training in the basics as wellas an introduction to splicing, terminat-ing, pulling and testing cables.

For those familiar with the basics, alsoavailable will be new courses on telecom,LAN, military FO and CATV networks.Of course, everyone can meet all the ven-dors and get hands-on training on the lat-est fiber optic components. They're plan-ning to build and test a full indoor/outdoorfiber optic cable plant during the confer-ence as part of the workshops.

The cost of Fiber U is $500.00.The conference is oriented to anyone

interested in learning more about thepractical aspects of designing, installingand maintaining fiber optic networks.This includes:

Electrical contractors Fiber contractors Users of fiber optic networks Systems integrators and VARs CATV and telecom planners, install-

ers and maintenance personnel Military personnel

With the "novice track" and all the sem-inars and workshops, "Fiber U" can ac-commodate all levels and still provide anintensive learning experience.

For more information, contact Fotec,Inc., 529 Main St., Boston, MA 02129.You can also call 800-537-8254 or Fax617-241-8616.

LOCATION

EIA HQ, DC JULY 13-15

TRITON COMM COLLRIVER GROVE, IL

TAMPA TECHNICAL INST. OCTOBER 18-20TAMPA, FL

COLOR TELEVISION

NEC DALLAS CAMPUS OCTOBER 18-20DALLAS, TX

NEC COMMERCE CAMPUSCOMMERCE, CA

VCR

SEPTEMBER 12-16

JULY 18-22OCTOBER 17-21

OCTOBER 24-28

Dates and locations of free ER "hands-on" workshops.


THE PIXXESSONAL NIAGARA FOR ELECIROACS AND COMPUTER SE ROC WIG LiteratureAOC"

Electronic Servicing & Technology is edited for ser-vicing professionals who service consumer electronicsequipment. This includes service technicians, field ser-

vice personnel and avid servicing enthusiasts who repair

and maintain audio, video, computer and other con-sumer electronics equipment.

EDITORIALNils Conrad Persson, EditorLinda Romanello, Associate Editor

CONSULTING EDITORSHomer L.Davidson, TV Servicing ConsultantVictor Meeldijk, Components ConsultantJohn E. Shepler, Audio ConsultantSam Wilson, Electronics Theory Consultant

PRODUCTIONElizabeth Ryan, Art DirectorBarbara Terzo, Assistant Art DirectorSusan Reale, ArtistEdmond Pesonen, Electronic Composition Mgr.Dorothy Kehrwieder, Production ManagerEmily Kreutz, Advertising ProductionPat Le Blanc, Phototypographer

BUSINESSRichard A. Ross, PublisherJohn Dorr, General ManagerFrank V. Fuzia, ControllerCatherine Ross, Circulation DirectorMelissa Nitschke, Data Processing ManagerCarol Licata, Data ProcessingDenise Pyne, Customer Service

SALES OFFICEElectronic Servicing & Technology76 N. Broadway, Hicksville, NY 11801516-681-2922; FAX 516-681-2926

Diane G. Klusner, Director of AdvertisingEmily Kreutz, Sales Assistant

EDITORIAL CORRESPONDENCE:P.O. Box 12487Overland Park, KS 66212913-492-4857

loom&

NESDA ifsMember, Electronic Servicing Audit Bureau ot Circulations

Dealers Association Member

0639'

Electronic Servicing & Technology (ISSN 0278-9922)is published 13 times a year by CO Communications,Inc. 76 N. Broadway, Hicksville, NY 11801. Telephone(516) 681-2922. Second class postage paid atHicksville, NY and additional offices. Subscriptionprices (payable in US dollars only): Domestic-oneyear $24.75, two years $45. Foreign countries-oneyear $30.75, two years $57. Entire contents copyright1994 by CO Communications, Inc. Electronic Servicing& Technology or CO Communications, Inc. assumes noresponsibility for unsolicited manuscripts. Allow sixweeks for delivery of first issue and for change ofaddress. Printed in the United States of America.

Postmaster: Please send change of address notice toElectronic Servicing & Technology, 76 N. Broadway,Hicksville, NY 11801.

CO Communications, Inc. is publisher of CO The RadioAmateurs Journal, Popular Communications, Micro -Computer Journal, CO Radio Amateur (Spanish CO), COAmateur Radio Equipment Buyer's Guide, CO AmateurRadio Beginner's Buyer's Guide. Popular Communica-tions Communications Guide, and Electronic Servicing& Technology.

LP' AFSMINTERNATIONAL

ASSOCIATION FOR SERVICESMANAGEMENT INTERNATIONAL

Computer products/servicesdata sheets

Eagan Technical Services offers a col-lection of data sheets that describes theproducts and services they offer to usersas well as servicers of personal comput-ers. This is an international depot repairand parts company.

The brochure describes the repair ser-vices they offer for PS/2, Compaq, Delland Grid system boards, LCD and plas-ma displays, and mechanical assemblyrepair and refurbishing.

Products offered by the company, as de-scribed in the brochure, are the TK-1000and TK-2000 diagnostic systems for IBMPS/2 and Microchannel compatible com-puters, schematic diagrams of personalcomputers and monitors, system boardsales and exchange, proprietary electron-ics components, and disposable andmaintenance items for computer service.

Circle (15) on Reply Card

Computer replacementparts brochure

PartsPort, Ltd., announces the avail-ability of its brochure of Hard -to -FindComputer Repair Parts. This four -pagebrochure lists many of the products of-fered by the company, including monitorflyback transformers, IBM proprietaryICs, and a selection of other semiconduc-tor devices.

In addition to stocking a broad selec-tion of computer and peripheral compo-nents, the company offers assistance infinding or reproducing parts.

According to the brochure, "We canmachine or mold replacement parts forATMs, laser printers, check sorters, bank-ing equipment, telecommunicationsproducts and obsolete equipment. Sendus a sample piece for evaluation.


Test accessories catalog

ITT Pomona Electronics' new 36 -page,full -color, New Product Test AccessoriesCatalog introduces over 100 new prod-ucts, including Logic Analyzer Test Ac-cessories, IEC1010-Safe Probes andBanana Jacks.

Among the products highlighted are anew logic scope probe, insulated scopeprobes, oscilloscope probes and DMM testlead kits, IEC1010 probe leads, fusedprobe kits, grabbers, cable assemblies and

Nervy( Int kwisanes

New ProrhicisLBW

ITT Pomona ElectronicsIII ltNNo ,uMr,\1

adapters. Also featured are test clips andadapters for the latest IC devices, includ-ing the MC68360, 80486SLE, MC68HC-11 and other devices emerging in the mar-ketplace. Other new products that arefeatured include boxes, test strips and lab-oratory power supplies.


STICI-IT1994 PURCHASING GUIDE

CALL TOLL FREE800 221-3203

HERMAN H. STICHT CO., INC.57 FRONT STREET

BROOKLYN, NY 11201

Test and measurementinstrument guide

Herman H. Sticht Company has issuedtheir new 1994 purchasing guide. Theguide contains 96 pages with informationand specifications on Sticht's completeline of hand and stationary tachometers,frequency meters, running time meters,insulation testers, stroboscopes, control-lers, static eliminators and more. In addi-tion, the catalog presents information onmultimeters and test instruments by lead-ing manufacturers worldwide.



Servicing electronic typewritersBy Dale C. Shackelford

Until recently, typewriter repair was aspecialty practiced only by trained ser-vice representatives who would drop bythe office at the most inopportune mo-ment to make the repair, or to cart off themachine for a week to perform the repairs.

Today, most electronic typewriters arelightweight, extremely portable and are arelatively inexpensive alternative to themulti -component computer. When anelectronic typewriter breaks down, re-gardless of the cost of the unit, the ownerwill typically attempt to have the unitrepaired. This is where the local electron-ic servicing technician can play a role.

Electronic, not electricTo begin, we must observe the distinc-

tion between an electric and an electron-ic typewriter. Electric units generally uti-lize an ac motor which powers a cam/gearsystem, that in turn drives the striking(print) mechanism against a ribbon, thenonto the paper. The most common elec-tric typewriters were manufactured byIBM, and were known as the Selectricseries. These machines, in most cases, re-quire servicing by a trained electric type-writer technician, as there can be literal-ly thousands of rods, gears, pulleys andother moving parts which must be alignedwith the utmost precision.

Electronic units, on the other hand, con-tain a minimum of moving parts, and relyprimarily on traditional integrated cir-cuitry to control various protocols such asprint speed, memory and other basic func-tions. Electronic typewriters may containRAM, ROM, PROM and EPROM cir-cuitry, all of which require the uniquerepair skills of the electronics technician.

Many electronic typewriters, regard-less of their capabilities, performance,price or manufacturer, exhibit many of thesame symptoms of wear, neglect or abuse.In addition, virtually all electronic type-writers require similar procedures for re-pair and maintenance. With this in mind,we can look at some of the most common

Shackelford is an independent electronic servicing technician.

RIBBON CASSETTE

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problems associated with these increas-ingly common electronic appliances.

Contaminated membraneWhen depressing a particular key (or

combination of keys) fails to result in atyped character, it is usually an indicationthat the unit has been exposed to mois-ture, dust or other contaminants whichhave found their way through the keysand between the conductive material onthe bottom of the key and the contacts onthe underlying sensor pad. These sensorpads, sometimes called membranes, are

extremely delicate, and special attentionto detail should be given in any attemptat cleaning them.

To determine if the problem lies withthe connection of a particular key, or else-where within the system, try to activatethe demonstration program found in mostelectronic typewriters. This program canusually be activated by depressing theCODE button, and pressing keys whichdo not indicate that they have a particu-lar CODE function (Figure I ). In manycases, the combination of CODE/D willaccess this program, though this will vary


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depending upon the make and model.When activated, the demonstration

program will print out a basic capabilitieslisting of the typewriter. If any of the char-acters are missing, or in the wrong orderon the demo printout, the problem willlikely be traced to one (or more) of theintegrated circuits, not the keyboard. Ifthe demo looks good, then the problem ismost likely a contaminated membrane.

Correcting membrane problemsTo repair a contaminated membrane,

remove the keyboard and membrane fromthe typewriter chassis. If any of the con-tacts on the membrane or the keypad areshiny, they should be cleaned and dressedby lightly rubbing them with a clean swaband a cleaning chemical such as tape headcleaning solution. It would be best to checkfirst to see what the manufacturer of thetypewriter recommends. If the cleaningsolution is too strong, or the contacts arerubbed too hard, the tracings will disap-pear, and the membrane will have to bereplaced. Once all contaminated areas ofthe membrane have been cleaned suffi-ciently, contacts will be flat black in color.

Before reinstalling the membrane andkeypad, it is a good idea to clean the con-tact points (usually a ribbon type connec-tor) where the membrane connects to theprinted circuit board. Once the membraneand keypad are reinstalled, you can checkthe operation without totally reassem-bling the unit if you bypass the safety in-terlocks that may be used on the machine.

Power supply problems

Another common malady suffered byportable electronic typewriters concernsthe power supply, especially off -boardtransformers (power packs). While off -board power supplies do allow typewrit-ers to be made smaller and lighter, thesesystems are very inefficient and createmany problems for the consumer. Manyproblems can be traced to one of threepoints: the transformer, the small wiresconnecting the transformer to the type-writer or the receptacle/switch system.

As with most transformers, power packunits may be checked with a standard me-ter to determine power output, continuityof hookup wires and plug integrity. If suf-ficient power is reaching the typewriter,the problem is likely to be found in the re-ceptacle/switch combination.

Power receptacle/switches (Figure 2)


O 1

COMMON GROUND

+ FROM OFF -BOARD fPOWER SUPPLY 0

. COMMON GRCUND

FROM BATTERY

Figure 3.

are notorious for causing problems in awide variety of appliances. Over time, thereceptacle may become loose, causingbroken connecting wires or solder con-nections. Play may develop in the recep-tacle so that the plug will not fit tightlyinto the socket (causing intermittent con-nections), or the spring/switch may be-come worn or broken, thereby allowingthe unit to operate only from one powersupply (batteries or off -board transform-er). Simply replacing the power pack orthe receptacle/switch combination shouldcure most of the power supply problemsencountered with these devices.

Look for the obvious

Before beginning service on any elec-tronic typewriter, be sure to check for the

obvious. Is there a good ribbon in the ma-chine? Is the ribbon the correct one forthe typewriter? Is the daisy wheel (orother typing element, including dot ma-trix head) in good condition and proper-ly positioned? Is the top cover closed?Many electronic typewriters utilize asafety interlock which will not allow themachine to operate if the cover is not se-cured. Are the batteries in good conditionand properly installed? Is the voltage se-lection switch in the proper position? Anyone (or more) of these basic observationscould save hours of diagnosis time.

General maintenanceSome machines which may be brought

in for service will require only generalmaintenance to make them operate like

new. Some typewriters will inform theowner/technician of the maintenance re-quired through a prompt or code on theLCD display (if applicable) while othermachines will be brought in only after theowner detects a problem such as a grind-ing noise or deteriorating performance.

When a typewriter is accepted for main-tenance, remove all accessories (ribbons,print wheels, etc.) and blow out the unitwith dry, compressed air to remove anyloose particles of contaminants. Shortblasts of air should remove the typicalcontaminants such as correction paper/fluid residue, dust and hair, while a softbrush will aid in removing contaminantssuch as tape or dust bunnies which areoften lodged in small gears.

Pinch rollers, paper carriages and feedsystems can usually be cleaned with aspecial typewriter cleaning fluid, whilesome technicians have found tuner clean-er to work well in these applications whenused sparingly. Once the internal work-ings have been cleaned, make sure to runa few sheets of paper through the systemto absorb any pockets of moisture whichmay have collected. Small amounts oflight weight (white) lithium grease canthen be applied to the plastic gears, andcarrier guides may be lubricated withpowdered graphite, when used sparingly.

With the increased use of portable elec-tronic typewriters both in business and inthe home, many manufacturers of theseproducts are looking to train service per-sonnel, supply technical support and in-formation to those interested in becom-ing authorized service representatives. Ifyou feel that typewriter servicing wouldmake a good sideline to your current prac-tice, contact the manufacturer of these de-vices for more information. Three of thebiggest names in portable electronic type-writers are listed below.

Brother International CorporationTypewriter DivisionP.O. Box 1332Bartlett, TN 38184-1332

Canon U.S.A.. Inc.One Canon PlazaLake Success, NY 11042

Sharp Electronics Corp.Sharp PlazaMahwah, NJ 07430


A hard disk drive primerBy John A. Ross

If you plan to service personal comput-ers, you'll have to know about hard diskdrives. Anyone who has worked withcomputer technology understands the im-portance of that storage device. You onlyneed to lose data, or work with someonewho has lost data because of a hard diskdrive failure, to fully realize just how im-portant hard disk drives are.

In light of that importance, this articledescribes the components of a hard diskdrive, details the different types of drives,provides some basic information aboutinstalling different drives, and lists sev-eral excellent reference sources that coverhard disk drives and their interfaces.

Hard disk drive basicsHard disk drives rely on electromag-

netism for data storage and transfer, justas floppy disk drives do. Data is stored ona hard disk when an electric current flowsthrough an electromagnet. The electro-magnetic action generates a magneticfield that is stored on the hard disk.

Data is read from a hard disk when thesame electromagnet passes over the diskand encounters the stored magnetic field.When the encounter occurs, an electricalcurrent identical to the current originallyused to store data on the disk is generated.

In the case of the hard disk drive, theelectromagnet is the head, while the diskis coated with a material that containsmagnetic "domains." Before the head has"written" anything on the disk, the mag-netic fields created by the magnetic do-mains are oriented randomly throughoutthe coating, and thus cancel one anotherout, along with any resulting field polarity.

As the disk spins, the head is movedacross its surface. The head is aerody-namically designed, and it can truly besaid to be "flying" just above the disk, inthe air movement created by the disk'sspinning motion

Writing to the diskWhen the computer "writes" data to the

disk, the magnetic field generated by the

Ross is a technical writer and microcomputer consultantfor Ft. Hays State University, Hays, KS.

Figure 1. This is what a typical hard disk drive looks like with its cover removed. The drive as-sembly includes heads, cylinders, and platters. Each platter in the hard disk drive has two sides.In operation, read/write heads move across the platters while data is stored in tracks and sec-tors on the platters.

current through the head is focused in thearea between the head and the platter. Theclose proximity of the strong magneticfield to the magnetic particles aligns thefield domains on the platter into magnet-ic flux.

Reversing the current flow through thehead coils also reverses the direction ofthe flux on the disk. The reversal of fluxdirection places a flux reversal on the plat-ter. Each pattern of flux reversals repre-sents the recording of data on the disk.

Reading from the diskPassing a drive head over an area of the

platter that holds flux generates current in

the drive head. The direction of the cur-rent in the head matches the direction ofthe flux. Passing the head over an areawhere a flux reversal occurs causes thecurrent in the head to change direction.

The weak reversed currents match thecurrents that passed through the head dur-ing the recording of data. Here, the head isin its "read" mode. The electronic circuit-ry in the drive and controller amplify andtranslate the currents back into usable data.

Because the read/write head is so closeto the disk's surface during operation, itis important that no dust, dirt, smoke orother contaminants be allowed to enterthe disk drive. Thus hard disk drives are


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Figure 2. The IDE interface card has no "intelligent" electronics and works simply as an adapter.In IBM-compatible microcomputers, a 40 -pin interface cable connects the drive to its interfacewhile IBM computers use either a 40 -pin or 72 -pin cable.

sealed at the factory in clean rooms. Ahard disk drive is, therefore, a sealed unitthat works as a magnetic storage devicefor data.

Data encodingThe specific pattern of flux reversals on

the surface of the disk that represents a bitof data is called the encoding method.Figure 1 shows a picture of a typical harddisk drive with its cover removed. As thefigure shows, the drive assembly includesheads, cylinders, and platters. Each plat-ter in the hard disk drive has two sides.During its operation, read/write headsmove across rigid platters while data isstored in tracks and sectors on the platters.

PlattersGoing back to Figure 1, the disk por-

tion of the hard disk drive is a set of cir-cular platters made of aluminum, plastic,or glass substrate. Data is stored on thecoating that covers both sides of plattersubstrate. Lower -cost hard disk drives

have oxide -coated platters while more ex-pensive hard disk drives have a thin plat-ing of metallic alloy on their platters.

The difference in performance betweenthe two types of coatings may be appre-ciated by considering the number of mag-netic domains per inch of track. Coatedmedia hold up to 20,000 magnetic do-mains, while plated media hold up to50,000 domains. In addition, plated plat-ters are much harder than coated plattersand, consequently, are less susceptible tohead crashes.

As mentioned, some drives have glassplatters. Glass platters have a smoothersurface than the aluminum platters andcan hold more data.

TracksIf you removed a platter from a for-

matted hard disk drive and could see theformatting information, you would see aseries of concentric circles. The circlesare the "tracks" that hold data. With 1,000or more tracks per inch of media, hard

disk drives have high track densities. Thismeasurement defines the number oftracks that can be written to a platter.

SectorsEach track is divided into an equal

number of magnetically -marked sectionscalled sectors. In turn, each 512 -byte -

large sector has a sector heading that in-cludes an identification field that holds anidentification number that ranges fromzero to 65,535.

Formatting a hard disk drive writes theidentification field or address informa-tion to the hard disk. The address informa-tion includes the cylinder number, headnumber, and sector number of the currentsector. Before any read or write operationoccurs within the hard disk drive, the con-troller compares the address informationwith the desired cylinder, head, and sector.

Sector sparing reduces the number ofavailable sectors per track by one. Theset -aside sector is used to store defect in-formation. Although sector sparing re-duces the capacity of the hard disk drive,it hides defects from application software.

Zone Bit Recording places more sectorsper track on the outside tracks of the plat-ter. Because of DOS limitations, each sec-tor contains 512 bytes of data.

Read/write headsHard disk drives have one read/write

head per platter side. The read/writeheads of a hard disk drive are pieces ofmagnetic material that pass over a mov-ing disk surface that carries a magneticflux. Because the common read/write headis a small horseshoe magnet wrapped withcoils of wire, a generated magnetic fieldis concentrated between the prongs of thehorshoe, or U. Disk drive logic sets up thecurrent that passes through the coils. Asyou know, the direction of the flow of theelectric current dictates the field's polarity.

Read/write heads are part of a simplemechanical assembly. Above and beloweach platter, a head is fastened to a spring -loaded arm that holds it against the plat-ter. Thus, when the drive is not powered,the head lands on the disk.

When the platters spin at full speed, acushion of air develops between the headand platter and lifts the head off the plat-ter. The resulting gap between the headand platter is between 5 and 20 millionthsof an inch. Any type of particle that blocksthe gap causes the heads to read or write


Version

2.02.1 up to 3.303.30 up to 4.04.00 up to 5.05.00 up to 6.2

Partition Limit

16 Megabytes32 Megabytes32 Megabytes512 Megabytes2 Gigabytes

Table 1. A disk partition is a section of a harddisk drive set for a specific operating systemand amount of space. DOS allows four parti-tions. Different DOS versions have differentpartition limits. Those limitations are shown inthis table.

improperly. A head crash occurs when thehead and disk damage one another duringthe landing. Rough handling or a smallparticle between the head and disk cancause head crash.

Three different types of read/writeheads-monolithic, composition andthin-film-are used in today's hard diskdrives. The amount of head gap and trackdensity varies from low to high, respec-tively, with the type of heads used in thedrive. As the previous example of headoperation shows, the larger monolithicheads have an iron -oxide core wrappedwith electromagnetic coils.

In the case of the composite process, aceramic housing covers a ferrite core bond-ed to glass. Another manufacturing pro-cess that involves the use of integrated cir-cuit techniques to deposit the read/writeelements results in thin film heads. Thin-film heads offer a more precise magnetic

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pulse, so they allow high track densities.When working with hard disks, know-

ing the meaning of a few head -relatedterms can help your understanding ofoverall drive operation. Seek time is theaverage time the heads take when mov-ing between one track to another track.

CylindersReferring to Figure 1, the platters of a

hard disk drive are stacked vertically. Theidentical track numbers on each plattertaken together create a cylinder. As theheads pass over the platter, the tracks un-der all the heads are the cylinder.

Spindle motorA spindle motor is a direct action motor

that spins the platters in a hard disk drive.A ground strap dissipates static generatedby spindle motor operation and groundsthe spindle case motor.

Stepper motor actuator, andvoice -coil actuator

A stepper motor actuator moves theheads over the platters. The stepper motorrotates a precise number of steps and con-verts those steps to linear motion. Inex-pensive hard disk drives use stepper mo-tor actuators.

A voice -coil actuator also moves theheads over the platters but uses a solenoidto influence the movement. Voice coil ac-tuators move the heads faster than step-per motor actuators.

40 -PIN CONNECTOR

MARKED WIRE

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InterleaveMany hard disk drives can transfer data

faster than the microprocessor can acceptit. Interleaving forces the drive to slow itsreading of data by renumbering the sec-tors. Rather than number the sectors se-quentially, interleaving staggers the num-bers of the sectors.

The staggering approach allows thecomputer to store data for one sectorwhile two others are under the head. Dur-ing one revolution of the platter, the sys-tem will read and store six sectors of data.In three revolutions, the system will readand store the data from all sectors.

PartitionA partition is a section of a hard disk

drive set for a specific operating systemand amount of space. DOS allows fourpartitions. Different DOS versions havedifferent partition limits. Those limita-tions are shown in Table 1.

Hard disk drive interface typesAs mentioned during the brief discus-

sion of hard disk drive operation, specif-ic patterns of flux reversals that store databits are called encoding methods. Harddisk drives rely on two encoding methodscalled modified frequency modulation orMFM and run -length limited or RLL.

Aside from using different encodingmethods, hard disk drives also utilize dif-ferent interfaces. We can classify the ST -506/412 and ESDI interfaces as disk in-terfaces. The SCSI and IDE interfaces are

POWERCCNNECTOR

Figure 3. The IBM-compatible IDE interface cable connection.


classified as system interfaces. However,the SCSI and IDE interfaces utilize theESDI electronics for communicatingwith the disk. The electronics that givethe SCSI and IDE drives their namescommunicate with the drive controller.

MFM hard disk drivesBoth the MFM and the RLL hard disk

drives use a ST- 506/412 interface. MFMhard disk drives use a fixed- length mod-ified frequency modulation encodingscheme accomplished on the drive con-troller card. With the encoding schemeconverting the digital bits received fromthe central processing unit into a patternof magnetic changes or "flux reversals,"the flux reversals are stored on the harddisk drive.

Simply put, the encoding scheme en-closes clocking information with the datapulses. Since each flux reversal on thedisk is evenly separated by time, the be-ginning of each bit also is separated fromthe others, and each bit uses an identicalamount of linear space. Thus, the con-troller electronics can easily detect andcorrect single -bit errors. The MFM for-mat specifies that the drive will containseventeen sectors per track.

Important things to know aboutMFM drives

MFM drives usually have one termi-nating resistor pack and anywhere fromtwo to four -drive select jumpers. A 20 -pin drive data cable and a 34 -pin drivecontrol cable connect the drive to its con-troller card. If installing two MFM drivesin a system, each drive requires a data ca-ble. A dual drive control cable will workfor both drives. The first drive attaches tothe last connector on the cable while thesecond drive attaches to the middle con-nector. MFM hard disk drives require alow-level format.

RLL hard disk drivesHard disk drives using the RLL encod-

ing scheme have fifty percent more spaceand a higher transfer rate than drives usingMFM encoding. Thus, in theory, a drivethat has a capacity of 40 megabytes withMFM encoding can store 60 megabyteswith RLL encoding. The key concept toremember when comparing the MFM andRLL encoding schemes is density.

The MFM encoding scheme utilizes aregulated amount of flux reversals. RLL

encoding divides the MFM bit cells intothree RLL bit cells and introduces an ir-regularity into the flux reversals becauseany of the three RLL bit cells may havea flux reversal. Note that the number offlux reversals per track does not change-only the regulation. As a result, the den-sity of data doubles but the magnetic den-sity stays the same.

In the paragraph above on RLL, thewords "in theory" were used in compar-ing the capacity of MFM and RLL drives.One cannot simply match an MFM-en-coded drive with an RLL controller andreceive more disk space.

While the encoding method cuts theamount of data -checking informationstored on the drive and has less flux rever-sals than an MFM drive, it requires morelogic than the MFM scheme. Consequent-ly, both the RLL controller and drive elec-tronics must have more precise timing.

RLL controllers must have a more so-phisticated error detection and correctioncircuit than MFM controllers. Since theRLL drives do not have the regular fluxreversals seen with the MFM drives, theencoding method is more prone to errors.

Rather than having a stepper motor, anRLL drive should have a voice coil actu-ator and employ thin film media. Steppermotors can introduce tracking problemsand temperature -induced errors. Thin-film media has a higher signal-to-noiseratio and a higher bandwidth. Drives thathave a voice coil actuator and use thinfilm media are called "RLL Certified."

Important things to know aboutRLL drives

Installation tip: RLL drives will have26 or more sectors per track.

Like MFM drives, RLL hard diskdrives usually have one terminating resis-tor pack and anywhere from two to fourdrive -select jumpers. As with its oldercousin, a 20 -pin drive data cable and a 34 -pin drive control cable connect the RLLdrive to its controller card. The same rulesthat apply for installing two MFM drivesin a computer system apply for RLL dri-ves. RLL hard disk drives require a low-level format.

ESDI (enhanced small deviceinterface) hard disk drives

In 1983, a group of hard disk drive man-ufacturers adopted a drive standard thatwould provide better error correction and

higher transfer speeds. By building theencoder/decoder circuitry into the drive,the design team managed to provide aninterface that could transfer 25 megabitsof data per second.

In practice, most ESDI drives have atransfer rate of 10 megabits per second.The higher transfer rate also results fromdrives formatted at 32 sectors or higherper track and a 1 to 1 interleave support-ed by the controller. A combination ofhigh data density and low interleave ratioallows a higher transfer rate.

Aside from the characteristics seenwith the drive, the ESDI interface also of-fers other features. The enhanced com-mand set within the controller allows theinterface to read the capacity parametersof the drive. Therefore, the interface cancontrol the defect mapping of the drive.In effect, this simplifies the installation ofthe ESDI drive set.

Installation of an ESDI drive does notrequire the use of a setup program or thewriting of a defect map by the installer.With the ESDI interface commanding thedefect mapping, the controller BIOS orthe system BIOS reads the drive tabledirectly from the drive. Since the com-puter system can read the drive defectmap, the defect list can be written as a fileto the drive.

Rather than having the installer type thedefect list from the keyboard, the ESDIinterface allows the controller and thelow-level format program to update thedefect list. Normally, the ESDI controllerBIOS includes a low-level format programand a surface -analysis utility program.

Important things to know wheninstalling ESDI drives

Installation tip: When installing anESDI hard disk drive, set the drive typeto one. The ESDI controller firmwarehandles compatibility problems. ESDIdrive specifications are factory -encodedon the drive. The firmware also containsthe low-level format program.

ESDI drives usually have one terminat-ing resistor pack and anywhere from threeto twelve drive select jumpers. Like theMFM and RLL drives, ESDI drives uti-lize one control cable and one data cable.The same rules for installing two MFMand RLL disk drives in a system apply toESDI drives. ESDI drives require a low-level format and usually have an inter-leave set to one.


SCSI (small computer systemsinterface) hard disk drives

Developed in 1979, the small comput-er systems interface (SCSI) works from alogic level instead of the common devicelevel. With the MFM, RLL, ESDI, andIDE disk drives, we mentioned control-lers in the same breath as the drive.

However, the SCSI is a pure interfaceinstead of working as a driver or a driveor a controller. A controller is inserted be-tween the SCSI interface and the drive.Each SCSI system can accommodateeight controllers with one controller work-ing as an interface between the SCSI andthe computer system.

Since the interface uses the logic leveland leaves the interface decisions to theattached devices, several different typesof devices can be attached to the SCSI in-terface. The interface can handle as manyas seven logical devices including harddisk drives, tape drive units, floppy diskdrives, scanners, CD-ROMs and otherperipheral devices. Jumpers on each at-tached device set a logical unit numberfor the device and identify them as logi-cal units for the interface.

Hard disk drives intended for use with

a SCSI system usually arrive as completeunits called "embedded SCSI drives."One circuit contains the drive. controller,and SCSI adapter. While this adds con-venience, it also limits the number ofdrives that can be attached to the SCSIsystem to seven.

With the controller portion of the setembedded within the drive, only onedrive can be attached to the controllerthrough a 50 -pin drive header cable. Also,each SCSI bus address on the adapter cansupport only one drive. If the task requiresmore than seven drives, add more SCSIadapters to the SCSI system.

Important things to know wheninstalling SCSI drives

Installation tip: When installing set thedrive type to zero. The on- board BIOSon the SCSI controller will take care ofany compatibility issues.

Technicians will find several terminat-ing resistor packs on the SCSI drive. Ifconnecting the SCSI drives as part of adaisy chain, remove all the resistors onthe drives that make up the middle of thechain. Only the first and last drives re-quire the terminating resistors. From

three to twelve jumpers set the logical unitnumber of a SCSI drive. Usually, SCSIdrives arrive already low-level formatted.

IDE (integrated drive electronics)hard disk drives

IDE hard disk drives have most of thecontroller functions built into the drivecircuitry. Consequently, the drive andcontroller are a matched pair. As withSCSI drives, the drive name "IDE" refersto the interface rather than the drive.Because of the integrated nature of thedrive, it will either connect to a limited -function -interface card installed in thesystem bus or directly to the motherboard.

Depicted in Figure 2, the interface cardhas no "intelligent" electronics and workssimply as an adapter. In IBM-compatiblemicrocomputers, a 40 -pin interface cableconnects the drive to its interface whileIBM computers use either a 40 -pin or 72 -pin cable. Figure 3 shows the IBM-com-patible interface cable connection.

All IDE drives use RLL encoding with36 or more sectors per track, some havemore than 16 heads, and some have morethan 1024 cylinders. All these character-istics are worth noting. Most computer

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Figure 4. IDE hard disk drives do not have terminating resistor packs. However, a set of jumpers on the underside of the drive can be used toconfigure the drive as a master or slave. On a Western Digital Caviar drive, those jumpers are placed as shown here.

system BIOS drive type tables have lim-its of 17 sectors per track and 16 heads.In addition, DOS will recognize a maxi-mum of 1024 cylinders for a hard diskdrive. Because of those three factors, theinstallation of an IDE drive requires atranslation of the drive physical informa-tion to logical information.

The physical information of a drive isthe actual number of heads, cylinders, andsectors per track in the drive. On the otherhand, logical information is the numberof heads, cylinders, and sectors per trackshown by the drive and seen by the sys-tem BIOS. To handle the translation, theelectronics contained within the IDEdrive and controller perform a mathe-matical calculation that matches the log-ical settings entered in the BIOS to theactual, physical values of the drive.

Important things to know wheninstalling IDE drives

Installation tip: When installing an IDEhard disk drive, select a drive type that isequal to or less than the size of the harddisk drive in megabytes. Never select atype that specifies a capacity larger thanthe drive. Let the IDE drive and controllerperform the translation.

IDE hard disk drives receive low-levelformatting at the factory. Using commonlow-level format programs on an IDEdrive after its installation may eliminate

the factory defect map and may damagethe drive. Some utility software applica-tions can low-level format an IDE drive.Without the use of traditional low-level for-mat, interleaving the drive is not required.

IDE hard disk drives do not have ter-minating resistor packs. However, a set ofjumpers on the underside of the drive canbe used to configure the drive as a mas-ter or slave. Figure 4 shows the locationof those jumpers on a Western Digital Ca-viar drive. Only applicable to AT -stylesystems, the first drive is called the mas-ter while the second is called the slave.Micro House International recommendsthat technicians installing two drives in asystem use drives made by the same man-ufacturer. Either connector on the IDE ca-ble may attach to the master or slave drive.

Hard disk drive reference sources

Because of space limitations, this arti-cle cannot provide all information abouthard disk drives and hard disk drive in-stallations. However, many fine refer-ences about the subject exist.

The Micro House Encyclopedia of HardDrives provides excellent, comprehensivespecifications for all hard disk drives anddrive controller cards. The three -volumeset (Set-up Guide, Drive Settings, andController Cards) is an essential tool foryour workbench and is available from:

Micro House InternationalP.O. Box 17515Boulder, Colorado 80308800 -741 -DATABBS: 813-441-8501

The book Upgrading and RepairingPCs, by Scott Mueller, provides not onlyinformation covering different hard disktypes but is a storehouse of informationabout microcomputer systems. Like theMicro House Encyclopedia set, Upgrad-ing and Repairing PCs is an essential toolfor your shop. The text is published by theQUE Corporation and is sold by mostbookstores. You may contact MuellerTechnical Research by phone, fax, BBSor by mail:

Mueller Technical Research21718 North MayfieldBarrington, IL 60010-9733708-726-0709FAX: 708-726-0710CompuServe ID: 73145,1566

Another very good reference for yourshop library is Troubleshooting and Re-pairing PC Drives and Memory Systems,by Stephen J. Bigelow, published byWindcrest/McGraw-Hill. Bigelow's textprovides an extensive overview of micro-computer hard disk drives and the proce-dures for installing all types of drives.


Removing conformal coatingsBy James L. Witcher

For many years, the use of conformalcoatings on electronic circuits was rarelyused outside of the military, where theywere common because of the special re-quirements of military equipment. Withthe growth of electronics into the indus-trial and consumer markets, however, newapplications that require coating are com-ing about. Trying to service these productscan become quite baffling. Following is adiscussion of conformal coatings, withsuggestions on how to service productswhich use them. With a little planning, therepair process can be made much easier.

The nature of conformal coatingsConformal coatings are typically plas-

tic films applied to the printed circuitboard (PCB) with a thickness of 0.001inches to 0.005 inches. Their purpose isto protect the PCB from the environmentin which they will be used. Examples in-clude traffic signals, hospital diagnosticequipment, automotive electronics, secu-rity alarms, public telephones, vendingmachines and more.

Moisture, solvent vapor, dust, fungus.and other contaminants can cause a cir-cuit assembly to malfunction or quit work-ing altogether. Conformal coatings aredesigned to prevent these outside factorsfrom affecting the functionality of thePCB. The choice of which type of coat-ing to use depends on properties needed.

Types of conformal coatingsMilitary specification MIL -I -46058C,

the conformal coating specification, listsfive types of conformal coatings: acrylicresin, silicone resin, polyurethane resin,epoxy resin and paraxylene resin (Figure1). These types of coatings comprise thebulk of those being used by both consum-er and military manufacturers.

Acrylic resinThe acrylic, Type AR conformal coat-

ing, is an economical, general purposecoating that is not recommended for usein harsh environments. AR coatings arethe easiest to apply and rework becausethey are easily removed with solvents.

Witcher is a Technical Applications Chemist for TechSpray, Inc.

Coating TypeMIL -I -46058CType AR

Type SR

Type UR

Type ER

Type XY

Resin Type

Acrylic Resin

Silicone Resin

Polyurethane Resin

Epoxy Resin

Paraxylene Resin

Figure 1. Military specification MIL -l -46058C,the conformal coating specification, lists thesefive types of conformal coatings. These types ofcoatings comprise the bulk of those being usedby both consumer and military manufacturers.

However, the resistance to moisture, fun-gus, and solvent is much lower than thatof the other types of coatings. The ARcoatings are also somewhat brittle whenfully cured causing adhesion problems inthermal cycles.

Rework and removal of the AR coating

is accomplished by dissolving the coat-ing in an appropriate solvent or stripper.Mechanical removal is also possible, butburning directly through the coating is notrecommended. Once the defective com-ponent is replaced, the area should becleaned and the AR coating reapplied.

Silicone resinThe silicone, Type SR coatings are very

popular because of their diverse charac-teristics. They are very flexible makingthem excellent choices for harsh temper-ature environments (hot or cold or rapidchanges). SR coatings have a high mois-ture/fungus and solvent resistance. Thesecoatings are generally considered "bestall around" coatings for most applications.

SR coatings can be removed usingchemical or mechanical means. Since thecoating is resistant to solvent, very strongchemical strippers must be used. Caremust be taken to prevent damaging theboard or components underneath the

Property. TypeAR

TypeSR

TypeUR

TypeER

TypeXY

Thermal Shock 2 5 3 2 3

Dielectric Strength 3 2 4 2 3

Moisture/Fungus 2 5 4 5 5

Resistance

Chemical Resistance 1 3 4 5 5

Ease of Repair 5 3 3 2 1

Flexibility 2 5 3 2 2

Removal Methods

Chemical 5 3 2 1 1

Thermal 3 2 4 3 2

Mechanical 4 3 4 4 4

Legend1-Poor, 2-Fair, 3-Average, 4-Good, 5-Excellent

Figure 2. Once the coating type has been determined, the removal process can begin. Selectthe process that will take the least amount of time and effort. Do not remove more coating thanis necessary.


coating. Because of the heat resistantnature of silicone coatings, burn -throughis not recommended.

Polyurethane resinPolyurethane, Type UR coatings have

very high solvent and moisture resistance.This type comes in two forms: one part andtwo part. Two part UR coatings offer quickcure times of one to three hours, but haveshort pot life once mixed. One part URcoatings are applied like conventionalcoatings, and then moisture in the air caus-es them to cross link or polymerize mak-ing them very durable. This type of URcan take up to three days to fully cure.

Because of the high chemical resis-tance of type UR coatings, very strongsolvents/strippers must be used to com-pletely remove the coating. Mechanicalremoval and burn can both be used to re-pair boards coated with a UR coating.

Epoxy resinEpoxy, Type ER coatings are primarily

two part systems with one exception. Thistype of coating is extremely resistant tomoisture and solvent making it impossibleto remove with a chemical stripper. (Thereare solvents that will remove epoxy resincoatings, but in general they will dissolveall the plastics used in making the PCB, aswell). Burn through and mechanical re-moval are the only practical means of re-pairing a PCB coated with the ER coating.

UV curable epoxiesThe exception to the two part epoxies

are UV curable epoxies. These are one -part systems that contain a photo initia-tor. When the liquid coating is exposed toultra -violet (UV) light, the initiatorbreaks up starting a chain reaction whichchanges the material to a solid plastic. Ineffect, the light acts as the "second part"in the epoxy system. This process is veryfast, taking less than 60 seconds. Pot lifeof the epoxy is greatly extended and pro-duction time is reduced.

ParaxyleneThe final type, paraxylene (Type XY),

is the most chemically and physicallytough coating. This is almost totally lim-ited to military use. Rework is practical-ly impossible since the coating is so resis-tant to solvent, heat and mechanical stress.

Removal methodsThe most serious drawback to using

conformal coatings is the difficulty in

repair. To replace a defective component,the coating must be removed so the jointcan be desoldered. Then once the com-ponent is reinserted, the surface must becleaned, dried, and the coating reapplied.Choosing the appropriate removal meth-od can help speed up the repair process.

Chemical strippingChemical stripping of the coatings is

the recommended method if large areasof the PCB are to be reworked. The typeof stripper depends on the coating used.Most manufacturers of conformal coat-ings offer a stripper specifically designedto remove their coating.

Two basic types of strippers have beenused extensively in the electronics mar-kets. Those based on methylene chloridetend to be very aggressive. The coating isremoved in a matter of minutes. Caremust be taken to remove the stripper be-fore it begins to attack the permanent sol-der mask or components underneath theconformal coating.

Because of the toxicity of methylenechloride (it is now considered a humancarcinogen), many companies have optedfor a different technology. Dibasic esters,n -methyl pyrrolidone, and other solventshave been used to formulate strippers thatare much safer to the user.

However, these coating removers re-quire much longer to work, up to 8 hours,and in some cases will not remove thecoating at all. To help speed up the remov-al process, place the boards in an oven at120F since many chemicals become acti-vated when heated. Consult with the man-ufacturer of the stripper to determine ifheat can increase aggressiveness.

Once the coating has been removed, itis imperative that the stripper be com-pletely rinsed off the board. Any remain-ing residue could cause the solder jointsto corrode. A polishing rinse with sol-vents containing alcohol can help insureremoval of all residue.

Thermal removalThermal removal is the direct applica-

tion of heat to the coating. Hot air, hotknives, and soldering irons are the mostcommon tools. This method is particu-larly handy for spot replacement of spe-cific components. Most often, the solder-ing iron is placed directly on the coatingto melt/vaporize it.

As with chemical removal, cleanlinessafter component replacement is very im-

portant. Burned or yellowed coatingshould be scraped off and the surfacecleaned with a solvent before reapplica-tion of coating.

Mechanical removalMechanical removal is recommended

for the tougher silicone, epoxy, polyure-thane and paraxylene coatings in spot re-placement applications. Mechanical re-moval can be as simple as scraping off thecoating with a sharp instrument. Severalcompanies in the electronics market man-ufacture systems for mechanical removalof conformal coatings.

A much less expensive route is to go tothe local hardware store and look for therotary hand tools. These are small instru-ments which often come with a variety ofbits ranging from wire wheels and grind-ing stones to intricate cutting tools.

When mechanically removing a coat-ing, care must be taken to prevent dam-age to the components underneath. Thepressure applied should be just enough toremove the coating. Excessive force canstrain solder joints and components. Afterthe components are replaced, be sure alldust and flux residues are cleaned beforereapplying the coating.

Steps used in reworkingThe first step in reworking a PCB that

has been conformally coated is to deter-mine what type of coating has been used.Only the most trained eye or very expen-sive laboratory equipment can determinethe type of coating simply by observation.The best method is to contact the manu-facturer of the PCB and get the coatingspecifications. It is imperative that thesame type of coating used in the manufac-turing process is used in the rework.

Mixing of coating types can have veryunpredictable results. An epoxy coatingwould not adhere well to a silicone resincoating and vice versa. Different coatingtypes expand and contract at differentrates with changes in temperature. Whentwo different types are used on a singleapplication, changes in temperature cancause them to pull apart from one anoth-er and from the substrate.

Once the coating type has been deter-mined, the removal process can begin. Se-lect the process that will take the leastamount of time and effort. Figure 2 andthe discussions on removal methods canhelp make this choice easier. Do not re-move more coating than is necessary.


Recoating the reworked portionof the circuit

After the PCB repair has been complet-ed, the board should be prepared for re-application of the conformal coating.Proper cleaning is critical. Rememberthat the coating not only protects the PCBfrom outside contaminants but also trapsany existing contaminants permanently.A solvent designed fordefluxing will helpremove the flux and flux residues, and apolishing rinse of deionized water fol-lowed by polar solvents like isopropanolor ethanol will help insure that all ioniccontaminants are removed.

The boards should be completely drybefore attempting to re -coat. Any trappedmoisture can cause the coating to blisterand fail in the field. If necessary, place theboards in an oven at 120F for a couple ofhours prior to coating.

Finally, using the coating type recom-mended by the manufacturer, reapply tothe repaired board. Four types of applica-tion methods are commonly used: dip,pour, brush and spray. Dip and pour tech-niques are for completely re -coating theentire surface. Brushing allows a thickcoat to be applied to a specific area, whilespraying allows for a thinner coat to beapplied. Be sure to re -coat to the samethickness as the original coating.

The electrical and physical propertiesof a coating depend on its thickness. Man-ufacturers will often specify a minimumthickness for optimum performance. Al-low the coating to dry and cure as ex-plained in the directions.

Specialized coatingsProper repair of the conformal coating

will insure that the PCB will function asbefore. Further, there are several coatingsavailable to help eliminate specific prob-lems. Encapsulants are viscous materialsdesigned to cover and protect specificcomponents or areas on a PCB. Strain re-lief materials help cushion componentsand areas that are placed under stress. Andmany adhesives are available to repairboards and components.

The use of conformal coatings is be-coming quite common. The more compo-nents that are packed onto a board, themore sensitive that board becomes to out-side contamination. Repair of these de-vices does not have to be difficult, but itdoes require a little planning up front.

Test Your ElectronicsKnowledgePower calculations and miscellaneous11 Sam Wilson

Figure 1. What is the dB gain of this amplifier?

I. A certain power amplifier increasesthe input power by 3dB. If the input poweris 5.2W, what is the output power?

2. A certain transmission line intro-duces a 3dB loss to input power. If theinput power is 9.8W, what is the poweroutput from the transmission line?

3. Figure 1 shows an amplifier with asignal voltage input of 1.3V and an out-put signal voltage of 3.6V. What is the dBgain of the amplifier?

4. What is a stroboscope used for'?

5. What does VCO stand for in a phase -locked loop?

6. Consider the Lissajous pattern ofFigure 2. The horizontal sinewave fre-quency is known to be 450Hz. What isthe vertical frequency?

7. What is the impedance of four 40speakers in parallel.

8. Is the following statement correct?:

Wilson is the electronics theory consultant for ES&T.

Figure 2. In this Lissajous pattern, the hori-zontal sinewave frequency is 450Hz. What isthe vertical frequency?

Partition noise does not occur in a MOS-FET.

A. correctB. not correct

9. Is the following statement correct?:Decreasing the gain of an amplifier willautomatically increase its bandwidth.

A. correctB. not correct

10. Is the following statement correct?:The drain voltage of an enhancementMOSFET is never greater than 36V.

A. correctB. incorrect

(Answers on page 46)


Electronic servicing forperformance and reducedenvironmental impactBy Dr. Mo Tazi

The chemicals used in servicing today'selectronic equipment and systems aredramatically changing, and will continueto do so throughout the decade as morestringent environmental regulations areenacted which restrict and/or ban manyof the traditionally used chemicals. Alter-native chemistries have already been de-veloped which reduce a product's poten-tial to cause environmental impact, and itis these chemicals which will become thenew mainstays of the electronics industry.

Today, a service technician has the op-tion of choosing between a standard prod-uct, typically formulated with chloroflu-orocarbons (CFCs) or chlorinated sol-vents, which have the potential to depletethe atmosphere's ozone layer, or select-ing a new alternative product specifical-ly engineered for high performance andlower environmental impact. Under-standably, no one wants to choose be-tween performance and environmentalimpact, because a product that sacrificesone attribute at the expense of another isnot an ideal option.

Alternatives are availableFortunately, there are no -compromise

alternatives now available that achievereduced environmental impact as well asdramatic gains in performance. By mak-ing a careful and informed choice, it ispossible to select a product that offerscomparable or even superior perfor-mance to the conventional formulation,while, at the same time, minimizes thepotential impact on the environment.

In real -world electronics service, per-formance is the primary reason a techni-cian selects a particular product for thedesired application. After all, perfor-mance is something tangible that you caneasily see. Environmental impact, how-ever, is harder to imagine, because it takes

Tazi is Director of Research and Development at

Chemtronics Inc.

Performance CFC-FreeCleaner

ConventionalCFC Cleaner

Product Required for 33.0 94.0Water Soluble OilRemoval(MG Solvent/1MG Oil)

Water Soluble OilRemoval Rate(MG/IN2 Sec.)

Ozone Depletion 0.00 0.78Potential

Table 1. Alternatives have been found for CFC-based cleaner/degreasers that actually performbetter while having little or no ozone -depletion potential. This table provides a comparisonbetween two such products.

an understanding of the chemistry of spe-cialty products to grasp the impact thattheir usage has on the environment.

How chemicals affectthe environment

Consider what happens when a tradi-tional CFC-based compressed gas dusterwas used for routine contamination re-moval on a computer keyboard. As thedust and contaminants are blown away,chlorine is released into the atmosphere.This chlorine eventually reaches theozone layer and begins a destructive thin-ning process. Halting this so-called thin-ning of the ozone layer is at the heart oflegislation that is restricting the use ofCFC-containing products, and will ulti-mately ban them from use.

The ozone layer is a natural protectiveshield that helps prevent harmful ultravi-olet (UV -B) rays from reaching theearth's surface. This layer is vitally im-portant because excessive ultraviolet ra-diation may lead to numerous healthproblems, including cataracts and skincancer, and may also restrict the body'sability to ward off disease. Moreover,

overexposure of UV light can potentiallyinterfere with photosynthesis, thereby re-sulting in lower yields of crops, and mayalso affect the growth of photoplankton,which is a primary source of food formarine life.

Through extensive research, it has beenlearned that CFCs, substances that havebeen commonly used in many electronicschemicals, may be a factor in depletingstratospheric ozone. Ozone moleculescontain three atoms of oxygen. When anelectronics service technician uses aproduct that contains CFCs or chlorinat-ed solvents, chlorine atoms are released.These chlorine atoms eventually reachthe upper atmosphere where they attackozone, causing one oxygen atom to breakaway from the ozone molecule, whichthen forms chlorine monoxide. The chlo-rine monoxide combines with anotheroxygen atom to form a new oxygen mole-cule and a chlorine atom. This begins achain reaction in which the destructiveprocess is repeated as additional ozonemolecules are broken apart.

Now if the technician had selected analternative, non-CFC product to clean the


Performance

Product Required forRosin Removal(MG Solvent/MG Oil)

Rosin Removal Rate(MG/IN2 SEC.)

Ozone DepletionPotential

CFC-Free ConventionalFlux Remover Flux Remover

101.0

4.0

0.00

3673.0

(1.3

0.35

Table 2. Alternatives have been found for CFC-based flux removers that actually performbetter while having little or no ozone -depletion potential. This table provides a comparisonbetween two such products.

computer keyboard, there would havebeen no ozone -depleting substances re-leased to damage stratospheric ozone.

Regulatory issues andenvironmental impact

Understanding the myriad environ-mental impact regulations is a complextask; however, only a very basic under-standing of these regulations and the sub-stances they affect is necessary. The twomost important measures which impact

the electronics industry are the MontrealProtocol, which was adopted in 1987 andamended in 1990 and 1992, and the U.S.Clean Air Act of 1990. In simple terms,these regulations require the reductionand eventual elimination of all ozone -depleting substances. Under the U.S.Clean Air Act, phase -out began on fullyhalogenated CFCs commenced in 1990,and carbon tetrachloride followed in1992. Methyl chloroform, also known as1,1,1-tricloroethane, a chlorinated sol-

vent, began phase -out in 1993.At present, Class I substances will be

systematically reduced until they areeliminated entirely in the year 1996. It isimportant to note that these regulationsare subject to further amendment, whichmay change phase -out dates. In addition,many states and municipalities have en-acted environmental legislation that ismore stringent than current national orinternational regulations. Through thesemandates, electronics servicing techni-cians will find themselves forced intochoosing alternative chemicals simplybecause the traditional products they haverelied on will no longer be available.

How to make an informed choiceAs regulations become more stringent,

it will steadily become more important forthe user to know exactly how a particularproduct impacts the environment, as wellas how it affects the circuitry that the prod-uct will be used on. Choosing a chemicalproduct may seem difficult these days,with all the talk about CFCs, chlorinatedsolvents and ozone depletion. But it isn'tas hard as it may seem to make a decisionas to which specialty chemical to selectfor a particular electronics application.

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July '994 Electronic Servicing & Technology 21

Many electronics chemical manufac-turers provide information relating to aproduct's potential environmental impactthrough information on the label. Techni-cians should look for information aboutsuch chemicals as:

chlorofluorocarbons (CFCs), hydrochlorofluorocarbons (HCFCs), chlorinated solvents (Cl. solvs), volatile organic compounds (VOCs), hydrofluorocarbons (HFCs), and ozone depletion potential.

With this information clearly providedon a product's label, an electronics tech-nician can quickly and intelligently com-pare products and choose the one thatoffers the lowest environmental impactwhile meeting the desired performancerequirements.

Applications and alternativesCFC-containing products have been

popular because they remove a wide vari-ety of oils and contaminants, evaporatequickly and generally have excellent ma-terial compatibility: that is they don'tchemically attack other materials. Be-cause these products offered such de-pendable performance, manufacturersdid not seek alternative formulations untilconcern arose over potential environmen-tal concerns.

Choosing an alternative product mayrequire more care to be taken on the partof the technician to ensure compatibilitywith components and PCB substrates

because new chemicals may not offerbroad -based material compatibility; thatis, they may cause damage to some mate-rials. However, alternatives exist for justabout every segment of electronics ser-vice and repair, including:

contamination removal, cleaning and degreasing, flux removal, testing for intermittent circuitry

(freeze spray), desoldering components.

Cleaning and degreasingIn electronics cleaning and degreasing

applications, such as cleaning/degreasingof VCRs and personal computers, one ofthe most popular conventional agents hasbeen trichlorotrifluoroethane. An alter-native chemical that will not contribute tothe depletion of the ozone layer has beendeveloped. It penetrates tight areas to re-move oils, greases, dirt and fluxes whileevaporating quickly. See Table 1 for acomparison of the CFC-based productwith the newer non-CFC-based product.

Flux removal

Defluxing agents are commonly usedfor spot flux removal as well as cleaningrelays, switches and connectors. Heremany products were formulated withCFC-based solvent blends. Today there isa broad range of alternative products, spe-cially formulated to effectively removespecific flux types. One alternative CFC-free flux removal chemical removes or -

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ganic rosin fluxes and ionic soils offers ex-cellent material compatibility and has noozone -depleting potential. See Table 2 fora comparison of performance of a CFC-containing cleaner/degreaser with a new-ly developed CFC-free cleaner/degreaser.

Testing for intermittent circuitryWhen repairing PC boards, circuit re-

frigerants, also known as freeze sprays,are typically used to locate intermittentelectrical components and connections,or to cool an entire printed circuit board.As was the case with compressed -gasdusters, R12 (dichlorodifluoromethane),a CFC with an ozone depletion potentialof 1.0 has been one of the most widelyused. An alternative has been found thatexhibits superior thermal properties andhas no ozone -depleting potential. It

quickly chills to -60F, then evaporateswithout leaving a residue.

Desoldering

Desoldering products and methods areevolving to complement the new alterna-tive products. Today's high-performancedesoldering braids are commonly avail-able in rosin -fluxed versions, on both con-ventional and static dissipative bobbins.

Rosin -fluxed braids insure clean, con-taminant -free desoldering and typicallyprovide the quickest wetting action andbetter heat transfer over the pad or junc-tion. The highest quality rosin flux braidsmeet military standard requirements.

One of the newest developments in des-oldering braid is no -clean flux, whicheliminates the cleaning process after des-oldering and leaves almost no residue.

Conclusion

As more alternative products enter themarket and as environmental regulationsbecome increasingly stringent, it is be-coming more important that a user of spe-cialty chemicals has complete informa-tion on the product before making apurchase decision. Today's alternativespecialty chemicals match or exceed theperformance of conventional formula-tions with the advantage of reduced envi-ronmental impact. By becoming moreaware of how specialty chemicals per-form, their performance characteristics,and what impact the chemicals may haveupon the environment, service techni-cians can best select the right product forthe application.


Troubleshooting the CD laser headassemblyBy Homer Davidson

When a CD player is brought in for ser-vice, the condition of the laser head as-sembly may be the factor that determinesif the unit is worth repairing. The CD laserassembly is so costly that, if it's defec-tive, many owners will replace the com-pact disc player instead of having it ser-viced. The technician can save a lot ofvaluable time and trouble in CD servic-ing by first making sure that the CD headassembly and beam assembly are func-tioning, by performing a few quick laserhead tests (Figure 1).

Clean up timeBefore attempting to measure the laser

head beam, clean off the lens assembly.Dirt and dust on the lens assembly mayproduce skipping and poor tracking. Inmost CD players, the laser head assem-bly is covered by a flapper or disc assem-bly and cannot readily be seen. Of course,in the portable and boom box combina-tion CD player, the lens assembly staresright back at you.

Clean the lens with a lint -free cottonswab or cleaning paper found in CD clean-ing kits. Camera lens cleaning solution isideal. Wipe the lens gently to avoid dam-aging the supporting spring. Blow theexcess dust away from the optical lenswith a can of compressed air dust spray,available at electronic and camera outlets.

SafetyThe laser head assembly is a delicate

and critical component that should be

Davidson is a TV servicing consultant for ES&T.

Figure 1. The portable laser power meter will accurately indicate if the laser diode is emittingsignal against the underside of the CD disc.

handled with care. Keep fingers and toolsaway from the optical lens assembly. Re-member, the infrared laser light is invisi-ble. You can't see it. The laser assemblycan be dangerous to your eyes. Never lookdirectly into the laser beam or into the lensassembly. Keep your head at least 30cm(12 inches) from the lens assembly. Ob-serve the warning labels found on theCD player.

The optical laser pickup assembly typ-ically consists of the objective lens, fo-cus -tracking coils, collimating lens, beamsplitter, semi -transparent mirror, photodetectors, monitor and laser diodes.While working around or removing thelaser assembly, wear a grounded wriststrap to prevent electrostatic dischargedamage. Static electricity can damage the

sensitive laser head assembly.The entire optical block is a single unit.

When you encounter a defective opticalassembly, you have to replace it as a unit.

Laser head propertiesThe laser head diode material may con-

sist of GaAs/GAAIAs, Ga-Al-As, or GA -AL -AS material. The wavelength of thelaser head diode may vary from 750nm to820nm. The wavelength of the averageCD player laser is around 780nm. Thelaser power output may vary from0.15nW to 0.7nW (Figure 2).

There are several ways to test the laserhead emission:

an infrared card indicator, current and voltage measurements,

CD PLAYER DIODE MATERIAL WAVELENGTH LASER OUTPUT

ALPINE AUTO CD 5900 GaALAs 780nm 0.4mW

ONKYO DX -200 GaAs/GaAIAs 780nm 0.4mW

PIONEER PD7010 Ga-AL-As 780nm 0.26mW

SANYO CP660 775nm to 830nm 0.7mW

SONY CDX-5 GaAIAs 780nm 0.4mW

Figure 2. The laser diode material, wavelength and laser power output of the various CD players.


Figure 3. Voltage measurements across the emitter resistor can be converted to current, indicatng if the laser diode is functioning.

observation of the EFM waveform the laser power meter.

The easiest method to detect whetherthe laser is emitting an infrared signal iswith the infrared indicator card, but thecard does not indicate the amount of radi-ation emitted. The current and voltagechecks will give the correct current drawnby the laser diode, but it is necessary toget inside the unit to make this measure-ment. The laser power meter is the bestway to make this measurement: the meteris easily attached, and you can see theactual radiation measurement on themeter display.

Infrared card indicatorThe infrared indicator is a plastic card

that was designed for testing infraredremote controls. The card contains asmall square that glows when it is irradi-ated by infrared. Expose the infrared cardto ordinary light for at least 5 minutesbefore use. The small sensitive squarearea must be held directly over the lensarea for correct test results.

The infrared indicator card will indi-cate infrared emission, but will not indi-

cate the intensity, or tell you if the emis-sion is sufficient to operate the opticallens pickup assembly. This infrared indi-cator card can be purchased at most elec-tronic distributors, Radio Shack andRCA. The RCA part number is 153093.

Current and voltage checksThe laser diode emission checks can be

made by measuring the amount of currentdrawn by the laser diode. Most CD play-ers have a current label attached to the

assembly. For instance, the laser labelmay read 0138-499, indicating the cur-rent value is 49.9mA. Remember, the cur-rent increases when the temperature risesand decreases when it drops. If the cur-rent that you measure is much greater thanthe current specified on the label, the APCcircuit may be defective, or the laser diodemay have deteriorated. In either case, thelaser head assembly must be replaced.

In some CD chassis, a jumper wire mayoffer a test point where a current reading

Figure 4. Presence of the EFM (eight -to -fourteen) waveform indicates that the laser opticalassembly and rf amp are normal.


Figure 5. The laser power meter maytransmi4ers.

also be used to est infrared TV and VCR remote

can be obtained. Remove the plug andtake a current measurement of the laserhead diode. The current should match thatshown in the CD service literature or onthe laser power label.

Critical voltage testsAnother method to check the laser di-

ode current is with a diode voltage mea-surement. Actually, in this case, the cur-rent drawn by the laser diode is deter-mined by measuring the voltage across afixed resistor in the laser drive emittertransistor circuit (Figure 3). Often, thisvoltage is less than 1V. Check the laser

drive current by measuring the voltageacross R209 (1251). Then compare thevoltage measurement to the current labelon the pickup assembly.

The current drawn by the laser diodeequals the voltage divided by the resis-tance. In this case, where the resistance is12V, simply dividing by 10, or movingthe decimal point one place to the left, isa close enough approximation. If the volt-age across R209 is 0.48V, the currentshould be roughly 0.048A or 48mA. Thelabel on the pickup shows a reading of485, which indicates 48.5mA.

In this case, the laser pickup head is nor -

Figure 6. In most CD players, the infrared protecting interlock system must be defeated beforethe laser diode comes on.

mal. If the voltage measurement was 1V,the current would be too high and mightind_cate a defective laser diode. When thecurent is 10 percent or more in excess ofthe recommended value, replace the pick-up issembly.

EFM waveformsThe eight -to -fourteen (EFM) modula-

tion waveform must be present or the CDplayer will shut down after searching. Thecorrect EFM or "eye pattern" waveformis found downstream from the rf amp ICor zansistor (Figure 4). The presence ofthi; waveform indicates that the laserhead and if circuits are normal. Most CDplayers have a test point at which the eyepatern can be observed with the oscillo-scope. The EFM signal is fed to the sig-nal and servo processors and IC.

A low amplitude, jittery pattern, or noEFM waveform at all, may indicate adefective laser head assembly or if ampcircuits. Critical voltage and resistancemeasurements on the if amp transistor orIC may determine if the if amplifier isdefective. When you find an improperEFM waveform at the damp but measurenormal voltages on the rf transistor or IC,suspect a defective laser head assembly.In some cases you may have to replacethe if amp IC in order to determine if theEFM signal is present.

Although the presence of an EFMwaveform indicates that there is an rf sig-nal from the laser head assembly and therf circuits, it does not indicate if the laseris drawing excessive current or has cor-rect emission. The card indicator may in-dicate that infrared signal is present, buthcw much? Voltage and current mea-surements of the laser head circuits mayprovide a better indication of a defectivelaser diode, but this requires disassemblyof the CD player. The quickest and bestmethod to test the laser diode emission isw th the laser power meter.

The laser power meterMost CD player manufacturers recom-

mend a certain laser power meter or pro-vide them through the various electronicdepots. I use an LPM 5673 Sanwa laserpower meter (Figure 5). This low-pricedmeter is available through distributors.

This meter offers all required functionsfcr the control of laser light sources. Thisinstrument was particularly designed forservice of the compact disc and laser disc


Figure 7. The plastic lid of the portable CD player provides interlock protection as the lid musbe c.osed before the unit will play.

players, with a narrow and tillable probe.The instrument can be used on helium -neon lasers, such as used in distancemeters and linear measuring instruments.

Besides CD player tests, the tester cancheck the function of cassette compart-ment LEDs in video recorders and thetransmitting diode in infrared remote con-trols. The small black probe can be heldagainst the end of the infrared remote to

determine if the remote is emitting in-frared signals.

There are three measuring ranges:0.3mW, lmW and 3mW, which can checkall infrared lighting sources found in con-sumer electronics. The meter display in-cludes three measuring ranges of mea-sured light output with the upper scale at0.1mW, intermediate scale 0.3mW andlower scale of 0 to 0.3mW, and an extra

Figure 8. Check the suspected remote control with the intrared laser meter using the higherpower ranges.

scale for the display of the condition ofthe battery that powers the instrument.

A wavelength selector switch will setthe value length of the laser light at 633nmfor helium -neon -red lasers, and at 750nmto 820nm for CD and LD players and forinfrared measurement. The functionswitch determines the desired functionand measuring range. Also, the functionswitch turns the laser meter off and on.

Using a laser power meterTo use this meter, connect the test probe

to Jack 8. Set the function selector switchto the "Batt Test" position. If the meterhand stops in the good range, the batter-ies are normal and the tester is ready tocheck infrared light. The meter indicatorwill be deflected when the probe is turnedtoward sunlight or a service bench light.The probe should not be directly pointedat the sun or strong light, or the meter andprobe might be damaged.

Check the battery condition each timethe laser power meter is used. Observe themanufacturer's safety instructions in theservice manual of the CD player. Thespecified laser output is listed in most CDmanuals. Set the required measuringrange with the function switch. Set theswitch to the correct wavelength at750nm to 820nm for CD or LD players.

In cases where the specified output ofthe laser diode in the CD player is notknown, begin with the meter set to thehighest range. Most CD player diode out-puts are below the 1mW range. Rotate theswitch to the 0 to 0.3mW range. Positionthe probe with the round window over theCD lens assembly. You may have to movethe black probe around to get the maxi-mum reading.

If the probe is positioned at an angle tothe light beam, reflections will occur andresult in a distorted measurement. Strongoverhead light may cause an improperreading, so make your measurementsaway from the service center's main light-ing. When the round hole of the probe isdirectly over the lens opening, the laserdiode measurement will be maximum(Figure 6).

Keep the window of the probe clean ofI int, dirt and smudges. If the sensor win-dow is soiled, you'll get a distorted mea-surement. Clean off the sensor windowwith a cloth or swab moistened with thesame solution used to clean the lens areaof the CD player.


Read the measured value on the laserpower meter. Compare this measurementwith that given in the service manual forthe compact disc player. Adjust the laserpower output according to the manufac-turer's service manual. If the service man-ual is not available, compare the readingswith similar compact disc players.

Defeated interlockCD players have an interlock system

that prevents the laser from operating un-less there's a disk in the tray and every-thing is properly closed up. This interlocksystem must be defeated during servicein order to cause the laser diode to emitinfrared light. Notice in Figure 6, in thecase of this Sanyo CD player, a piece ofcardboard is placed between the LED andthe disc hole area keeping the LED lightfrom striking the interlock sensor, thusproviding operation of the CD playerfunctions. Place either a piece of plastictape or cardboard between hole and LEDto make the player function. Remember,the laser beam is on when this interlockis defeated. Keep your eyes away fromthe lens area.

In most portable CD players, the top lid

engages an interlock switch that turns onthe player and laser diode when the lid isclosed (Figure 7). A small screwdriverblade can be used to push down and en-gage the interlock switch, so that theintensity of the infrared light from thelaser diode in this RCA CD portable maybe measured.

Use a toothpick or a plastic pointed toolto defeat the interlock switch in otherportable models. Clipping a wire acrossthe interlock switch is another way to pro-vide CD player action when the unit isopened up for service. Do not forget to re-move the defeated interlock switch afterrepairs are made.

Testing remote control unitsThe laser power meter may be used to

check infrared remote control units aswell. If the plastic pickup is placed againstthe infrared source, the 1 mW or 3mWrange should be used (Figure 8). Com-parison measurements of the defeatedinfrared remotes can be marked or indi-cated on the meter scale. A weak or defec-tive infrared remote transmitter may pro-vide insufficient or no measurement onthe laser power meter.

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Tips on using test equipmentprobesBy Vaughn D. Martin

Parts I ,I1,andll of test equipment probeswere published in October and Novemberof 93 and in January' 94 .This article pro-vides a number of tips on using those testprobes.

The most common mistake in makingscope measurements is forgetting to corn -

Martin is Chief Engineer in the Automatic Test SystemDivision at Kelly Air Force Base.

pensate the probe. Improperly compen-sated probes can distort the waveformsdisplayed on the scope. The probe shouldbe compensated as it will be used whenyou make the measurement (Figure 1).

The basic low frequency compensation(L.F. comp.) procedure is simple. Con-nect the probe tip to the scope calibratoroutputs. Switch the channel 1 input cou-pling to dc. Turn on the scope and move

the CHI VOLTS/DIV switch to produceabout four divisions of vertical display.Set the sweep rate to 1 msec/div. Use anon-metallic alignment tool to turn thecompensation adjust until the tops andbottoms of the square wave are flat.

Choosing the right ground optionMake sure the ground in the device

under test (DUT) is the same as the scope

Compensated

1 ms dtv

Compensated

aty

0.1 -" 8.0 0 v

500es 2011

500 nsidiv

10 p.s/div

Over Compensated

1 OtreC las 100

(50 KHz signal)

1 ms/d v

Over Compensated

500 ne'div

10 sidiv

Under Compensated

1 ms/div

Under Compensated

500 ns/div

10 s,div

Figure 1. Compensating the probe.


Equivalent Circuit. Ground Lead Induced Noise.

Figure 2. An equivalent circuit of induced ground lead noise.

ground (don't assume it is). The scopeground is always common to the DUTground if you are using the power cordand plug and it's plugged into the samethree wire outlet system as used by theDUT. Check the circuit ground by touch-ing the probe tip to the point you think isground-before making a hard ground byattaching the ground strap of your probe.

When you're servicing a modern TVset, or other product that uses a full -wavebridge rectifier, however, be certain toplug the unit being serviced into the pow-er line through an isolation transformer.If you plug both the unit to be tested andthe oscilloscope into the same power linewithout isolation, at least one of the di-odes in the power supply will be short-circuited, and you will damage the unit tobe tested, and possibly the oscilloscopeas well.

If you intend to probe many points inthe same circuit and measure low fre-quencies, you can ground the circuit toyour scope once, instead of every timeyou move the probe. Connect the circuitground to the GND jack on the scope frontpanel. A special problem that occurswhen measuring very high speed signalsis ringing due to inductance in the ground -return path. Probes come with a widerange of grounding accessories, allowingyou to pick the right ground leads for theDUT's signal frequency range.

Optional accessories include BNC-to-probe-tip adapters and etched circuitboard (ECB) probe test jacks. Choosingthe right tip for the frequencies measuredcan minimize ground -path ringing.

long the lifetime of your probe tip. Whenyou are not using the probe, cover the tipwith the tip protector that is supplied withmost probes. Use the correct adapter, suchas an IC grabber or a retractor tip.

Don't use the probe to scrape throughinsulation, pry components from theirsockets, or move components. Don't usethe probe to hold down components whilesoldering in place. Remember, no matterhow well it is made, every probe has itsbreaking point. All probes should be usedwith care, as you would any other preci-sion tool.

Pitfalls in using probesWatch out for these pitfalls:

Using probes without checking low -frequency compensation.

Not using ground leads or usingground leads that are too long (that causeringing).

Connecting a probe ground lead to ele-vated ("hot") circuitry. The resulting dam-age is not covered by probe warranties.

Using too long a ground lead length.All things being equal, the shortest groundlead produces the highest ring frequency.

Induced noise in the probeground loop (tip shorted to the ground clip).

Figure 3. Induced noise in the ground loop withthe probe tip shorted to the ground clip.

OV

4V

177

50

Rs

Figure 4. The principle of operation of a biasoffset probe.

If the lead is very short, the ring fre-quency might be high enough to be out-side the passband of the scope, and/or theinput frequency content may not be highenough to stimulate the ground lead's res-onant circuit. In all cases, use the short-est ground lead, consistent with the needfor probe mobility. If possible, use 3 -inchor shorter ground leads, such as the lowimpedance contact (Z lead).

The correct probe grounding methoddepends on the signal's high frequencycontent, and the need for mobility be-tween test points. A 12 -inch ground lead

ov4V

1.7.27mA--> 450 fl

Caring for the probe tipFollowing a few guidelines will pro- Figure 5. A bias offset probe connected to a 5052 source.

Rp

rr7

50 11R scope


501,,

50 nR scope

Figure 6. A negative -going pulse acquired by a 10MS.I probe.

ov

-3.6V

-rIV

iv' 3.6 0

2ps

Effect of connecting a 450 ftBias Offset probe (offset = 0 V). Minus levelhas been reduced by 10%

Figure 7. The same pulse as that in Figure 6,acquired with a 45052 probe added.

OV REFV2

-40mV

-4V

3.6 0

I V 2p s

.,-set adjusted for -- 4 VSignal current at ;he -4 V level is zero.Current flow at ground level is maximum.Peak to pea -c amplitude remains the same10% down)

Figure 8. Adjusting bias to offset loadingeffects.

may be perfect for many lower frequen-cy applications. It will provide you withextra mobility, and nothing will be gainedby using shorter leads.

Ground loop noise injection

Another form of signal distortion canbe caused by signal injection into thegrounding system. This can be caused byunwanted current flow in the ground loop

existing between the common scope andtest circuit power line grounds, and theprobe ground lead and cable. Normally,all these points are, or should be, at zerovolts, and no ground current will flow.

However, if the scope and test circuit areon different building system grounds,there could be small voltage differences,or noise on one of the building ground sys-

tems. The resulting current flow (at linefrequency or noise frequency) will devel-op a voltage drop across the probe cable'souter shield, and be injected into the scopein series with the desired signal.

Inductive pick-up in ground loopsNoise can enter a common ground sys-

tem by induction into 5011 signal acqui-sition cables, or into standard probe ca-bles. Proximity to power cables or othercurrent -carrying conductors can inducecurrent flow in the probe's outer cable, orin standard 5051 coax. The circuit is com-pleted through the building system com-mon ground.

Prevention of ground loopnoise problems

To eliminate or minimize ground loopnoise problems, keep all signal acquisi-tion probes and/or cables away fromsources of potential interference. Verifythe integrity of the building systemground. If the problem persists, open theground loop:

by using a ground isolation monitor, by using a line isolation transformer

on either the test circuit or the scope, by using an isolation amplifier, by using differential probes.

NOTE: Never defeat the safety 3 -wireground system on either the scope or thetest circuit. Do not 'float" the scope, ex-cept by using an approved isolation trans-

OV REF _20mv -1)2

-3.8V

IV

Bias/Offset adjusted for -2 V.Load current distributed betweer thenegative and positive -going swings. Peak topeak amplitude remains the same (10%down).

Figure 9. Adjusting bias to equally distributecurrent.

former, or preferably, by using a groundisolation monitor.

Induced noise in probe ground leads

The typical probe ground lead resem-bles a single -turn loop antenna when it isconnected to the test circuit. The rela-tively low impedance of the test circuitcan couple any induced voltages in theprobe (Figure 2).

High speed logic circuits can producesignificant electromagnetic (radiated)noise at close quarters. If the probeground lead is positioned too close to cer-tain areas on the board, interference sig-nals could be picked up by the loop anten-na formed by the probe ground lead, andmixed with the probe tip signal.

Is this what my signalreally looks like?

If you suspect that the signal you'relooking at contains noise, moving theprobe ground lead around will help iden-tify the problem. If the noise levelchanges, you have a ground lead inducednoise problem. A more positive way ofidentification is to disconnect the probefrom the signal source and clip the groundlead to the probe tip. Now use the probe/ground lead as a loop antenna and searchthe board for radiated noise.

Figure 3 shows what can be found on alogic board, with the probe tip shorted tothe ground lead. This is radiated noise,induced in the single -turn loop and fed tothe probe tip. The significance of anyinduced or injected noise increases withreduced working signal levels, becausethe signal to noise ratio will be degraded.This is especially true with ECL, where

(Continued on page 43)30 Electronic Servicing & Technology July 1994

Tips on using test equipment probes (from page 30)

signal levels are 1 V or less.In order to eliminate this problem, use

an ECB-to-probe-tip adapter (test point)if possible. If this is not possible, use a Zlead or short flexible ground lead. Also,bunch the ground lead together to makethe loop area as small as possible.

Bias/offset probesA bias/offset probe is a special kind of

low -Z design with the capability of pro-viding a variable bias or offset voltage atthe probe tip. These probes are useful forprobing high speed ECL circuitry, whereresistive loading could upset the operat-ing point. They are also useful for prob-ing higher amplitude signals (up to 5V),where resistive loading could affect thedc level at some point on the waveform.

Bias/offset probes are designed with atip resistance of 4500 (10x). When theseprobes are connected into a 500 envi-ronment, this loading results in a 10%reduction in peak -to -peak source ampli-tude. This round -figure loading is moreconvenient to handle than that producedby a standard 5000 (10x) low -Z probe,which would work out at 9.09% under thesame conditions. Bias/offset probes al-ways present a 45052 resistive load to thesource, regardless of the bias/offset volt-age selected.

The difference between bias/offset andstandard low -Z probes lies in their abili-ty to null current flow at some specific

and selectable point on the input wave-form (within 5V). To see how bias/offsetprobes work, let's take a typical 10 x500Q low -Z probe and connect it in thecircuit (Figure 4). By taking a currentflow approach we find that at one pointon the waveform the source voltage is -4V; therefore, the load current will be:

4V/5500 = 7.27mA

Therefore, the voltage drop across the500 source resistance (Rs) will be:

7.27mA x 5052 = 363mV

And the measured pulse amplitude willbe 4 - 0.363V = 3.637V (E DUT), orabout 9% down from its unloaded state.

If we substitute the 5000 low -Z probewith a 4505/ bias/offset probe, the circuitwill look like Figure 5. With the bias/off-set adjusted for OV, the effect on the cir-cuit will be similar to a 5000 low -Zprobe, except for a small resistive change.

Figure 6 shows the source waveformacquired by a 10M52 probe. Figure 7shows the effect on the waveform whenthe 4500 probe is added. As expected, thepulse amplitude has reduced from -4V to3.60V or exactly 10% down.

Figure 8 shows the effect of adjustingthe offset to -4V. The -4V bias opposesthe signal at the -4V level and results inzero current flow, and the source is effec-

Figure 10. A basic setup for making adifferential measurement.

tively unloaded at this point. However,when the signal returns to ground level,there is a 4V differential between the topof the pulse and the bias/offset source.Current will flow and Ohm's law will dic-tate that the top of the pulse will go neg-ative by -40mV (10%).

Sometimes it is desirable to adjust theoffset midway between the peak -to -peakexcursions. This distributes the effect ofresistive loading between the two voltageswings. Figure 9 shows the effect ofadjusting the bias/offset to -2V. Currentflow will be the same for both signalswings, and they will be equally down by5%, for a total of 10%.

A summary of the use ofbias/offset probes

Bias/offset probes can be adjusted(within ±5V) to provide zero resistive(effective) loading at one selected pointon the input waveform.

Bias/offset probes can be used to sim-ulate the effect of pull-up or pull -downvoltages (within ±5V) on the circuit undertest (voltage source impedance is 45052).

Bias/offset probes always present atotal resistive load of 45052, and reducethe peak -to -peak amplitude of 50Qsources by 10%.

For simplicity, we have ignored theeffects of capacitive loading. Typically,bias/offset probes have less than 2pF tipcapacitance. Bias/offset probes like the


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Each month, ES&T brings you how-toservice articles on TVs...VCRs...comput-ers...CD players...microwave ovens...audio proucts and more. It's just the in-formation you need to do your jobeveryday.

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-0

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N

Cl)

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Cl)is

C

4- -E signal

E commonmode

IV p -p pulse

_FLw

5V p -p sine= 20 MHz

(not to scale)

Figure 11. A simplified block diagram of a device under test.

Scale: 100mV/minor div

0.5v p -p 'ON

WV10:1

50mV p -p

MAI ^^^100:1

NV\

5mV p -p

1000:1

Figure 12. "Cleaning up" a signal by increasing the CMRR.

Tektronix P6230 or P6231 have band-widths to 1.5GHz, 45052 input R, and1.3pF (P6230), or 1.6g (P6231) inputcapacitance.

They provide offset voltages of ±5Vdc,and function with IMO or SOSI input sys-tems (P623 I , 505I only).

The P6231 is designed to operate withthe Tektronix 11000 Series scopes, andobtains operating power and bias/offsetfrom the scope. Offset is selectable fromthe mainframe touch screen.

Differential probing techniquesAccessing small signals elevated from

ground, either at an ac level or a combina-tion of ac and dc, requires the use of dif-ferential probes and a differential ampli-fier system. One of the problems associat-ed with differential measurements is themaintenance of high common mode re-jection ratio (CMRR) at high commonmode frequencies. Poor common modeperformance allows a significant portionof the common (elevated) voltage to ap-pear across the differential probes inputs.

If the common mode voltage is pure dc,the result may be only a displayed base-line shift. However, if the common modevoltage is ac, or a combination of ac anddc, a significant portion may appearacross the differential input and will mixwith the desired signal.

Figure 10 shows the basic items neces-

Figure 13. The HP 1133A TV/video sync podprobe accessory.

sary to make a differential measurement.Figures 10a and 10b are accessories forthese measurements. The Tek 7A13 dif-ferential amplifier serves as a scope plugin and alleviates all offset problems. TheHP1141A differential active probe, and itspower module, the 1142A, provide a 1:1division ratio through FET inputs with200MHz bandwidth and a 3,000:1 CMRR.

In this example, two similar but un-matched passive probes are used. Theprobe ground leads are usually either re-moved or clipped together. They arenever connected to the elevated DUT.


Figure 14. The HP 1137 A 5kV high -voltage probe.

CMRR depends upon accurate match-ing of the probe -pair's electrical charac-teristics, including cable length. SystemCMRR can be no better than the differen-tial amplifier's specifications, CMRR de-grades as a function of frequency.

Figure II shows a simplified diagramof a DUT with a pulsed output of I Vppfloating on a 5Vpp 20MHz sinewave.CMRR at 20MHz is a poor 10:1 becauseof the unmatched probes.

Observed signal (referred to probeinput) = 1 Vpp pulse + (5V" sine/10 =I V" pulse + 0.5V1 sine.

Figure I 2a shows what the displayedwaveform might look like under the con-ditions shown in Figure I I. In compari-son, Figures I 2B and I 2C show what thedisplayed signal might look like at

CMRRs of 100:1 and 1000: I.

Differential probe typesThere are two general types of differ-

ential probes: passive matched pairs andactive one-piece differential probes. TheTektronix P6055 and P6135 passivematched probe -pairs provide a 100:1CMRR at 20MHz when used with appro-priate differential amplifiers, and can pro-vide CMRRs of up to 20,000:1 at low fre-quencies. (P6135, 10.000:1. P6055,20.000:1).

Active Differential ProbesPassive probes impose a limit on

CMRR at high frequencies because of thephysical and electrical characteristics,and the separation from the differentialamplifier. This barrier is overcome bymoving the differential amplifier out tothe probe tips on an active differentialprobe. Now lead lengths and electrical

Figure 15. The Tektronix P6015A 40kV high -voltage probe.

Figure 16. The HP 5363 time interval probe.

parameters can be accurately controlledto produce superior high frequencyCMRR performance.

The Tektronix P6046 active differentialprobe houses dual input FETs, a differen-tial amplifier, and a line driver in the probebody. A 10X dual attenuator can be usedto extend the basic operating range of thesystem. and various probe tips can be usedto access variously spaced test points. Atthe scope's end, a power supply and a cal-ibrated Volts/div switch provides ranges ofmV/div to 200mV/div when the scope

sensitivity is set to 10mV/div.Because differential signal processing

is performed at the probe tip, commonmode rejection can be as high as 1,000:1at 50MHz. Contrast this with 100:1 at20MHz for the best passive probe -pair

performance (See Figure 12). The P6046system is compatible with a wide rangeof scopes and measuring devices with sin-gle -ended IMS2 inputs. No external dif-ferential amplifiers are required.

Common mode linear dynamic rangeLinear dynamic range figures are

unique to active probes. and refer to themaximum voltage swing (dc + peak ac)between ground and the probe tip beforesome degree of non -linearity shows.

In the case of differential active probes,this parameter is called common modelinear dynamic range, and specifies themaximum voltage of the probe inputsfrom ground (dc + peak ac) before signalnon -linearity manifests itself. The P6046can access signals that are elevated up to


± 5V from ground (dc + peak ac) at lx,and up to ±50V with the 10x attenuator.

Two types of handyTV service probes

The HP 1133A TV/video sync pod (Fig-ure 13), gives clamped and unclampedvideo output, trigger output for line orframe, and is compatible to most standardbroadcast composite video systems.

This sync pod gives you TV sync trig-gering for most analog and digital scopes,and provides clamped or unclampedvideo outputs. You can view these signalon your scope's vertical channels. You

also have trigger outputs allowing you toview the video line of your choice.

This unit has a separate ac power mod-ule. It features a loop -through input (twofemale BNC connectors) which you candrive from 7552 sources. This loop -through feature allows you to loop a 7551signal through the sync pod, then connectit to a video monitor or other device. Theclamped and unclamped video outputseasily drive a high impedance ( 1 MO to10%2) probe connected to a scope.

The pod is compatible with broadcaststandards M, N, C, B, G, H, I, D, K, Kland L systems.

Test Your ElectronicsKnowledgeAnswers to the quiz(from page 19)

1. The output power is approximatelytwice the input power, or 10.4W. (SeeWDYKAE? in this issue.)

2. The output power is approximatelyone-half the input power, or 4.9W. (SeeWDYKAE? in this issue.)

3. 13.9W. If you tried to calculate thegain using the equation:

dB = 20log(V2/V1),you got the wrong answer. That equationonly works if the input and output impedances are the same. Calculate the inputand output impedances using:

P=V2/R.Then use the equation:dB = 10log(P2/P1).

4. It is used for measuring RPM (rev-olutions per minute).

5. Voltage controlled oscillator.6. See Figure 3. Note that horizontal

and vertical lines are drawn against thecurve. The number of times the curvetouches the vertical line divided by thenumber of times it touches the horizon-tal line is equal to the horizontal fre-quency divided by the vertical frequen-cy. In this case 3:2 = 450:fv. Therefore,fv = (450 x 2)/3 = 300Hz.

7. la It is calculated the same way asfour 4Q resistors in parallel.

Figure 3. To solve TYEK question number6, draw horizontal and vertical lines againstthe curve as shown here. The number oftimes the curve touches the vertical line divid-ed by the number of times it touches the hor-izontal line is equal to the horizontalfrequency divided by the vertical frequency.In this case 3:2 = 450:fv. Therefore, fv = (450x2)/3 = 300Hz.

8. The correct answer is A. Partitionnoise occurs when a few of the chargecarriers go (randomly) to the signal inputelectrode rather than the output elec-trode. That cannot happen in a MOSFETbecause the gate is insulated from thechannel.

9. The answer is A. Gain and band-width are tradeoffs in an amplifier.

10. The answer is B. The voltage onthe drain can be over 600V with respectto the source.

Another probe is the high voltage1,000:1 divider probes used on TV highvoltage power supplies. The probe shownin Figure 14 operates up to 5kV. However,if you need to go up to 40kV (peak pulse)you'll have to use one such as the oneshown in Figure 15. This also handles fre-quencies to 100kHz and has from 12pF to47pF shunt capacitance.

A time interval probeThe last probe we will cover is an unusu-

al one you may never have even thoughtof, but it proves very handy. Refer toFigure 16, this is an HP 5363A time inter-val probe. You use this instrument probewith frequency counters. But, first, let'sreview how a frequency counter works.

In greatly simplified terms, a counter isa gate that opens and allows a counter torun as long as the gate is enabled. Whenthe gate is closed, the count is totalized.Say the count is exactly 1,000,000 and thecounter has a 10MHz time base (crystal).That means the gate was opened for 0.1seconds so the waveform may have a10Hz frequency.

What if you have two channels and theinput processing circuitry and the delaysin the two input cables to this counter varyslightly. This can be a real problem is youare seeking extremely accurate and re-peatable measurements. This is whereyou can "equalize" each channel.

More specifically, taking a typical fre-quency counter, there are probes, internalcabling, and differential delays amount-ing to 700 picoseconds inside the timingchannel. Therefore, the absolute accura-cy of the time interval is an unknown butfixed amount. How can this be solved?

This time interval probe has a 20Vdynamic range of ±10V on each channelin 10mV increments. This guaranteestriggering at the same point on each chan-nel by merely measuring one channelwith an input signal and swapping thesame signal to the other channel andadjusting this time interval probe, by10mV increments, until the two channelshave exactly equal results.

The large variety of test equipmentprobes, standard and specialized, pro-vides the servicing technician with a num-ber of ways to extend the usefulness ofthe test equipment on the service bench.A knowledge of some of these probes andtheir use can help the technician use theavailable test equipment to its fullest.

.1() Electronic Servicing & Technology July 1994

NTSC Part ISync signals and timingBy Arthur Flavell

This is the first in a series of three arti-cles that will explore the NTSC video sig-nal and how it relates to servicing videoequipment. Part I looks at sync signals,their functions in circuit control and thecomposite nature of NTSC video. Part IIoutlines the luminance (black and white)and chrominance (color) signals. Part IIIshows how baseband video and audio sig-nals are used to modulate RF carriers foruse in video cassette recorders, broadcast,cable and MATV applications.

NTSC videoWhen color was added to television in

the early 1950's, the need for new techni-cal specifications and operating require-

Flavell is owner of an independent consumer electronicsservice center in Alaska

ments was apparent. The National Tele-vision Standards Committee (NTSC) wascharged with developing a broadcast sys-tem that would meet the needs of colortransmission, yet be compatible with theexisting monochrome (black and white)format. The NTSC color video signalstandard was born.

NTSC video is a composite signal. Com-posite simply means that several indepen-dent signals are mixed together to form asingle output. Included in the compositeare vertical synchronization (V SYNC),horizontal synchronization (H SYNC).luminance (Y) and chrominance (C).

What are sync signals?Sync signals are square wave pulse

trains with specific frequency, amplitudeand waveshape characteristics. Their pri-

mary function is to control the operationof the sweep circuits in a monitor or tele-vision receiver, creating a properly posi-tioned and stable reproduced picture. Inaddition, they are used as reference sig-nals for other circuits, such as head switch-ing and servo systems in VCRs.

In RF systems, sync produces a higherlevel of modulation than other elementsof the composite signal. For this reason,received sync signals are often used in thecontrol of AGC circuits. To ensure com-patibility and optimum operation amongthe many types of NTSC equipment inuse, sync signals must meet strict stan-dards of frequency, timing and waveshape.

Where does sync come from?Sync originates with the creator of the

video signal. In commercial facilities,

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such as broadcast TV or production stu-dios, a master sync generator is used. Inthe case of local origination, such as aconsumer camcorder, sync circuits in thecamera produce the signals.

Virtually every frequency in the NTSCstandard is mathematically related to thefrequency of the chroma subcarrier. Thisfrequency is specified as 3.579545MHzand is designated fc .

Sync signals are derived from a highlystable, crystal -controlled oscillator. Amaster oscillator using a frequency of 4fc(4 x 3.579545MHz) or 14.31818MHz iscommonly used. Because the frequenciesof sync signals are mathematically relat-ed to the chroma subcarrier frequency,they may be developed from the masteroscillator by frequency division circuits.

Horizontal syncThe horizontal sync signal controls left

to right scanning of the raster during pic-ture reproduction. The NTSC standardspecifies 525 horizontal lines for eachcomplete picture. The horizontal scan rateis fc divided by 227.5 or 15.734264kHz.The total time for one left to right scan isknown as the horizontal interval. Its dura-tion is the reciprocal of the scan rate or63.556pseconds.

The sync pulse occupies only a smallpart of the total horizontal interval. It is asquare wave in shape with a nominal dur-ation of 4.64pseconds. When the leadingedge of the sync pulse is detected, thesweep circuits reset the scanning electronbeam to the left side of the picture in aprocess known as retrace.

Retrace occurs very quickly relative tothe time of the left -to -right scan of thehorizontal trace. To prevent the retracefrom appearing to the viewer, the videocircuits are blanked off for a period oftime known as the horizontal blankinginterval. It has a nominal duration of11 psec (Figure 1).

Timing relationships during the hori-zontal blanking interval are critical toproper circuit operation. To provide easyreference to specific segments of the in-terval, different areas have been givennames. The front porch is a minimum1.27psec interval from the beginning ofthe blanking interval to the beginning ofthe sync pulse. The back porch is theinterval from the end of the sync pulse tothe end of the blanking interval. The breeze-way is part of the back porch and lies be-

tween the end of the sync pulse and the be-ginning of the chrorna subcarrier burst.

Each of these intervals has a specificduration. These are particularly importantwhen performing camera circuit align-ments. Errors in alignment can result incompatibility problems, unstable picturesor total loss of sync control. Follow themanufacturer's specifications for settingtiming intervals as closely as possible.

The sync signal must also meet ampli-tude requirements. The NTSC systemspecifies a standard video output of 1 Vpp

into a 7512 load. To make alignment eas-ier, this signal has been divided into 140parts known as "IRE" units. The baselinefor measurement is 0 IRE units and rep-resents the blanking level. The area from0 to 100 IRE units defines luminance lim-its. Sync occupies the area from 0 to -40IRE units. The sync voltage is 40/140 x1 V or 286mVpp. Errors in adjustment ofsync amplitude can result in erratic synccircuit operation. This may be evident ashorizontal jitter or loss of sync control andpicture tearing.

Vertical sync

The vertical sync signal controls top tobottom scanning of the raster. The rate ofproduction of complete pictures is calledthe frame rate. Its frequency is deter-mined by dividing the horizontal scan rateby the number of scan lines per picture(15.734264kHz/525) or 29.97Hz.

Video produced at the frame rate caus-es a noticeable flicker on the screen. Toeliminate flicker, a system of interlacedscanning was adopted. In interlaced scan-ning, all the odd lines of the picture arescanned vertically followed by a scan ofthe even lines. Each vertical scan, consist-ing of half the picture lines, is called a

field. Two fields produce one frame.Field 1, or the odd field, begins with a

full horizontal line and ends with a halfline. Field 2, or the even field, begins witha half line and ends with a full line. Eachfield contains 262.5 horizontal lines.Fields are scanned at twice the frame rate(59.94Hz). This rate, combined with thepersistence of the human eye, eliminatesperceived flicker.

The vertical sync pulse occupies aspace of three horizontal intervals (iden-tified as 3H) out of each field. The syncpulse initiates vertical retrace, the periodduring which the scanning beam is re-turned to the top of the screen. To prevent

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this event from being seen, the video cir-cuits are blanked for a period known asthe vertical blanking interval (Figure 2).

The vertical blanking interval begins3H before the end of each field. The lead-ing edge of the sync pulse begins a newfield. The first nine lines of the blankinginterval contain specialized sync signalswhich are half the width and twice the fre-quency of horizontal sync pulses. Theseare known as equalizing pulses and pro-vide synchronization of the horizontal cir-cuits when interlacing fields which alter-nately begin and end with half scan lines.

Note the differences in the two tracesof Figure 2 which illustrate the provisionsmade for interlace. Field 1 (upper trace)begins with line 1. Line 522, which is thelast line of video in field 2, is 1H wide.Compare it to line 260 (lower trace). Thisis the last line of active video in field 1and is only 1/2H long. The other half ofline 260 begins the blanking interval.

The half line difference at the top of thepicture is accounted for in the interval fol-lowing the sync pulse. In field 1, line 4 is1H wide. In field 2, line 266 is seen to behalf blanking pulse and half at blanking

level. Note that in field 1, this arrangementproduces a 3H interval of equalizing puls-es between the end of the sync pulse andthe next full -width horizontal interval(lines 4,5 and 6). In Field 2, there is a 2.5Hinterval in the same area (second half ofline 266 plus lines 267 and 268).

Vertical sync amplitude is specified at-40 IRE units, the same as H SYNC. Mis-alignment of V SYNC amplitude maycause vertical jitter, jumping or loss ofsync control, resulting in picture roll.

Working with sync signalsTroubleshooting or aligning video sync

circuits requires the use of an oscillo-scope. If you do a lot of camera align-ment, it is worthwhile to invest in a wave-form monitor, a specialized oscilloscopedesigned for use with video signals. A trig-gered sweep scope with delayed sweepcapability will also produce good results.

To observe horizontal waveforms, setthe time base to 1 Opsec per division. Setthe trigger input to "TV LINE." If yourscope is not equipped with this feature,connect the external trigger input to asource of H SYNC in the equipment un-

der test. This setup will display slightlymore than one horizontal interval. TheXIO or delayed sweep function will ex-pand the trace so specific segments, suchas the blanking interval and sync pulse,may be examined more closely.

To observe vertical sync waveforms,set the time base to 2psec per division. Setthe trigger input to "TV FIELD." Other-wise connect the external trigger input toa source of V SYNC in the equipment un-der test. This will display slightly morethan one field of video. The X10 or de-layed sweep may be used to expand thetrace so the blanking interval and syncpulse may be more clearly viewed.

The blanking interval of either fieldmay be viewed with this setup. Momen-tarily adjust the trigger level control to un-lock the display and then reset it. It maybe necessary to do this several times untilthe display locks onto the desired field.

Sync signals provide the reference forstable, compatible video in the NTSC sys-tem. An understanding of the source andnature of these critical signals will helpyou perform faster and more accurate ser-vice on a variety of video equipment.

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Ten important CD waveformsBy Homer Davidson

When you're faced with a malfunction-ing compact disc player, observation ofsome important waveforms in the variouscircuits of the unit may help to locate thedefective circuit. A laser power meter testwill determine if the laser diode is defec-tive (Figure 1). Absence of RF or EFMwaveforms may indicate a defective opti-cal assembly or RF amplifier transistor orIC. The presence of a PLL-VCO wave-form indicates that the VCO (voltage -controlled oscillator) circuits are func-tioning normally.

Presence of the focus error (FE) wave-form, which is used in making focustracking adjustments, across the focuscoil may indicate that the focus circuitsare normal.

A dead motor may produce a waveformthat is a straight white line, while a rotat-ing motor will produce a moving wave-form. Waveforms taken on the sled andspindle or disc motors may indicate thatall of the motor circuits are normal. Ob-servation of waveforms within the com-pact disk circuits may help to locate thedefective component.

Laser power meter measurementsThe best way to determine if the CD

player's laser circuits are functioning isto measure the output of the laser with alaser power meter. Excessively high orunusually low power may indicate a de-fective laser diode. In most cases, if thelaser diode assembly is defective the CDplayer will not be worth repairing.

Compare the laser power meter read-ing with laser power specification on theschematic or the CD player's power label.Check to be sure that the correct supplyvoltage is applied to the optical pickup as-sembly and observe the RF, or EFM,waveform to see if it looks correct beforeconcluding that the laser head assemblyis faulty.

Laser power adjustmentsLaser power adjustments are made to

insure proper operation of the laser diode.If the power output of the laser diode mea-

Davidson is a TV servicing consultant for ES&T.

Figure 1. Measurement of the infrared power output of the laser head assembly using a laserpower meter may uncover a defective laser diode assembly.

sured by the laser meter is near the valuespecified by the manufacturer's servicedata, most likely the laser diode is normal.

A low EFM waveform may indicate adefective diode. In some optical pickupassemblies, the VR adjustments mountedon the laser head assembly are adjustedat the factory and should not be touched.Often, laser power adjustment is neededonly after replacing the laser diode opti-cal assembly.

To check the laser power and make anynecessary adjustments, place the powermeter probe over the lens assembly andnote the meter reading. Remember, neverlook directly at the laser lens assembly,and always keep your eyes at least a footaway from the laser when the unit is oper-ating. With the interlock defeated, the las-er diode will emit infrared light.

Locate the power adjustment (VR) onthe main board or optical assembly. Checkthe manufacturer's test points and differ-ent control adjustments on the printed cir-cuit board. Adjust VR so that the laserpower output corresponds with the valuespecified in the service literature.

Test points and adjustmentsMost CD players have test points and

VR control adjustments on the main PCboard. Often, however, the laser head ad-justment is located on the optical assem-bly. Locate all test points before you try

to take scope waveforms. Besides beinguseful in locating the cause of a defectivecircuit, the same test points may be usedfor making adjustments as well. Checkthe manufacturer's service literature fortest points and VR adjustments.

Adjustments to the compact disc play-er should be made in an established se-quence. Some manufacturers specify thissequence: laser power, PLL-VCO, focusoffset, tracking offset and tracking gain.Other manufacturers list the required or-der of adjustments as laser power, skew,HF or RF level, focus gain, tracking gain,PLL-VCO, focus offset and tracking bal-ance. Special screwdrivers or alignmenttools may be needed for some of these ad-justment screws. All adjustments aremade with a test disc playing.

Waveform 1-RF or EFM signalA normal RF or EFM signal will indi-

cate that the laser diode optical assemblyand RF transistor or IC are functioning.The EFM waveform may be observed atpin 20 of the RF amp (IC101) (Figure 2).You may find a test point given in themanufacturer's service literature on themain PC board (TP-RF). If the EFM sig-nal is not present, the player may searchand shut down. Check the laser diode andRF circuits in the case of constant shutdown of the CD chassis.

The normal EFM waveform should


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Figure 2. The EFM or eye pattern waveform may be observed at pin 20, or at the test point (TP-RF) in the CD player.

have a good eye pattern, represented by aclear-cut diamond outline. A vibrating orjittery eye pattern may indicate poor ad-justment. Correct adjustment is to makethe diamond -shaped area as clear as pos-sible without excessive jitter (Figure 3).

To adjust the EFM signal, locate the RF,HF or EFM scope test points and level orgain control on the main PCB. Check theRF pattern on the scope. Adjust the tan-

gential adjustment screw for maximumwaveform or voltage reading as given inthe service manual.

For example, in the RCA MCD-14lCD player, adjust the control so that theEFM signal waveform is 1.3Vpp on theoscilloscope. Similarly, in a Sanyo CP660model, adjust the HF-EFM waveform to1.5Vpp on the oscilloscope. A clean-cutand normal EFM waveform confirms that


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Figure 4. The PLL-VCO waveform voltage can be measured andFigure 3. A good EFM waveform voltage should have a clear-cut dia- adjusted from ground (bottom) to white or dark line. Some manufac-mond shape with very little jitter. turers use a frequency counter to adjust for the correct frequency.

the laser pickup assembly and RF ampcircuits are normal.

Waveform 2-PLL-VCO signalPresence of the phase -locked loop volt-

age -controlled oscillator (PLL-VCO)waveform indicates that the EFM voltagehas reached the digital signal processorand servo IC. The VCO oscillator outputsignal is compared to the edge of the EFMsignal read from the disc. The PLL-VCOoscillator adjustment can be made withthe oscilloscope and frequency counter.

Some manufacturers use a frequencycounter to set the frequency of the PLL-VCO, while others make the adjustmenton the oscilloscope (Figure 4). Adjust-ment of the PLL-VCO frequency must becorrect so that the optical lens assemblyfollows the disc motor and responds todropouts caused by defects on the surfaceof the disc.

Locate the coil or transformer on thePC board, and connect the oscilloscope tothe correct test points. Play a test disc. Ob-serve the waveform on the scope. Adjustthe coil until the specified dc voltage isfrom ground to a white or dark area on the

4

waveform (1.2V to 1.5V). In a similarmanner, connect the frequency counter tothe correct test point and adjust the coilfor the correct frequency listed in the ser-vice manual. Follow the manufacturer'sPLL-VCO adjustments.

Waveform 3-Focus error signal (FE)Presence of the focus error (FE) signal

waveform indicates that the correct focussignal is reaching the RF amp to the focusservo IC (Figure 5). Adjust focus gain andoffset for maximum output. The focusoffset may include the RF and EFM ad-justments, or they may be separate adjust-ments, depending on the manufacturer ofthe CD player.

Again, depending on the manufacturer,the focus offset adjustment may be calledthe jitter or eye pattern adjustment. Thefocus offset adjustment is about the sameas the jitter adjustment (Figure 6). Thisfocus adjustment can be made with a stan-dard music compact disc and an oscillo-scope. Connect the scope to the circuit testpoints on the pc board and play the disc.Adjust the VR focus offset adjustmentuntil the EFM or RF waveform is maxi -

Figure 5. The focus error (FE) signal is taken at the RF amplifier IC ortransistor circuit.

Figure 6. The jittery or bouncing EFM waveform may indicate improp-er focus error adjustment.

mum, and displays a sharply defined dia-mond -shaped pattern.

Waveform 4-Focus coilIf you're able to observe a focus coil

waveform, you know that the focus sig-nal is reaching the coil itself (Figure 7).The FE signal is sent from the focus -tracking servo to a focus driver IC or tran-sistor that drives the focus coil located inthe optical lens assembly.

If the focus drive signal was missing atthe focus coil, you would observe a hori-zontal white line on the oscilloscope atthis point. The focus error signal can bechecked at the FE output terminal of thefocus tracking servo IC, then followed tothe focus driver and then observed at thefocus coil leads (Figure 8). If you suspectthat the focus coil may be open, turn pow-er to the CD player off, then check conti-nuity of the coil using the low ohms rangeof the ohmmeter.

Waveform 5-Tracking error signal(TE)

If you are able to observe the trackingerror (TE) signal waveform at the focus -


Figure 7. Connecting the oscilloscope across the focus coil winding indicates if signal is presentat the coil assembly.

tracking servo, you have confirmed thatthe tracking signal has reached this point.The TE input and output (TEO) signalsmay be traced with the scope (Figure 9).

Usually, the tracking gain control islocated at the TE input terminal of the IC.The presence of normal TE input and out-put signals indicates that the tracking sig-nal is good to this point in the circuit.

When you observe a normal TE signalat the input terminal of the tracking focusIC but not at the output (TEO), the prob-lem may be improper supply voltage tothe IC, or a defective tracking -focus IC.Check the focus (FE) signal input and out-put before you conclude that the IC is thedefective component.

To perform the tracking offset or bal-ance adjustments, connect the scope tothe TE signal test point and play a testdisc. Adjust the SVR control so that the

TE signal waveform is vertically sym-metrical relative to OV. You usually won'tneed to perform the tracking gain adjust-ment unless you have replaced the focusoptical assembly or control.

Adjust the tracking gain so that thewaveform is not varying or jumpingaround (no large waves). Adjust the track-ing gain adjustment only after the focusand tracking adjustments are made.To make this adjustment, connect theoscilloscope across the tracking coil ter-minals and adjust tracking coil gain con-trol for 1.8Vpp to 2.2Vpp. Follow the man-ufacturer's tracking offset and gainadjustments.

Waveform 6-Tracking coilWhen the CD player is first turned on,

the tracking and focus assembly can beseen searching, even if the player shuts

down. Often, this indicates that the focusand tracking assemblies are normal. Thetracking offset (TEO) signal can bescoped at the TEO terminal of the focus -tracking -sled servo IC. The tracking sig-nal is fed to a tracking driver IC or twodriver transistors. The driver output sig-nal is applied to the tracking coil wind-ing. A waveform taken at the tracking coilindicates if signal is present (Figure 10).

Waveform 7-No motor movementObservation of the waveform at the mo-

tor terminals will reveal whether or notthe drive signal is reaching the motor. Ifyou observe a straight line, no signal isreaching the motor. Although a normalmotor waveform will not show muchmovement on the scope, several lines maybe seen together indicating that the motoris operating. A straight white line indi-cates no signal applied to the motor ter-minals (Figure 11).

Waveform 8-Sled motor movementIt is difficult to see a slide or sled motor

operating while the disc is playing, as themotor is enclosed under the main PCboard. A quick waveform taken at the sledmotor terminals will indicate if the motoris operating. If the motor is operating,you'll see several thin lines on the scope(Figure 12). If you don't see a waveformhere, trace the motor wires back to themain board. Often, the motor wires aresoldered or plugged into the main PCboard.

Check the motor waveform at the motor

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Figure 8. The focus error output (FEO) and tracking error output (TEO) signals are fed from the focus/tracking/sled IC.


4Figure 9. The tracking error (TE) signal can be signal traced with thescope from tracking IC to tracking driver and tracking coil.

Figure 10. The tracking error (TE) waveform found across the trackingcoil terminals. -01.-

Figure 11. No motor movement may show a white line wavefo-m with- Figure 12. The sled motor movement may be seen as varying lines ofout any motor lines. a scope waveform taken at the slide motor terminals.

plug connections. Sharp pointed instru-ment prods pushed down inside the plugarea will produce a good waveform. Clipthe ground lead of the probe to commonground, since most motor windings are atground potential.

The slide or sled motor is controlled bya signal from the same focus -tracking andsled servo IC. The slide motor control sig-nal may be connected to the sled IC ampli-fier and to transistors or IC drivers. Insome sled circuits, there may be a push-pulldriver transistor in each leg of the sledmotor terminals. In this case, one side ofthe slide motor terminals is not grounded.

Waveform 9-Spindle motor movement

The disc or spindle motor rotates thedisc platform. The spindle motor is con-trolled by a signal from the digital signalprocessor and CLV servo IC. The disc orturntable motor is a variable speed motor:it starts at around 500rpm when the laserpickup is at the center of the disc, andslows down as the laser pickup moves to-

ward the outer rim of the CD (to approx-imately 200rpm).

The master clock and spindle motorcontrol circuits are fed to a spindle motordrive circuit that may contain two drivertransistors or IC CLV servo. The disc mo-tor is locked in with a correction signalfrom the CLV circuitry.

Defects in a spindle motor may causeit to be dead and not rotate, or may causeit to operate at the incorrect speed. Thewaveform applied to the spindle motor ofa Sanyo CD player is shown in Figure 13.

Waveform 10-Oscillator waveformsBy observing the waveforms of crystal

controlled oscillators waveforms in thedigital servo and RAM circuits, you maybe able to determine if supply voltage isapplied to the IC processor and the com-ponent is operating. When the crystal -controlled oscillator is not functioning,you may assume the defect may be in theIC processor circuits.

The 4.19MHz crystal oscillator pins 31and 32 of system control IC and 8.4672

4Figure 13. The spindle motor waveform may form lines close togetherand move up and down as the motor rotates.

Figure 14. A 8.4672MHz crystal oscillator waveform found at sins 53and 54 of a Sanyo CP660 player.

MHz crystal oscillator on pins 53 and 54of digital control processor in a SanyoCP660 CD player may indicate IC302 andIC401 are normal (Figure 14). The tim-ing control generator oscillator on pins 53and 54 of an Alpine 5900 auto CD play-er may indicate a normal digital signalprocessor and CLV servo IC502.

ConclusionObservation of waveforms throughout

the compact disc player may help thetechnician quickly isolate a defective cir-cuit or component. The most importantwaveform found in the CD players are theRF or EFM waveforms. Without thisEFM waveform, the compact disc playerwill not operate.

Confirming that the laser diode is nor-mal using a laser power meter test makeseasy CD servicing. Check the manufac-turer's service literature for correct laseroffset and gain adjustments. The manu-facturer may use special adaptors andalignment procedures, so check the ser-vice literature.

1"' r ItlIt1I111II

11111


What Do You Know About Electronics?

The "Toss it" syndromeBy Sam Wilson

For years, the United States has beengradually painted into a corner; and,unless you start to do something about it,you're going to have your outdoor picnicson a mountain of garbage.

How many times have you heard thesestatements?

"If it costs less than $100.00, it is cheap-er to throw it away than it is to fix it."

"It's not worth fixing. You can get anew one for about $60.00.

"Even if I wanted to fix it, I couldn'tget parts for it."

"I'll tell you what, I'll give you $5.00for it on a trade in."

So, an AM/FM receiver goes to thelandfill because it needs a two -cent resis-tor. A small black & white TV receivergoes to the landfill because it needs a five -cent capacitor. A clothes dryer goes to thelandfill because it has a broken wire. Andon and on and . . . .

Used electrical equipment is fightingfor space in a landfill already cloggedwith "disposable" diapers, hamburgerwrappers and containers for householdcleaners that will last 500 years withoutdeteriorating.

In the next few years this country isgoing to be hit with a problem that manypeople are blissfully unaware of. Land-fills are going to start closing down be-cause there is no place to make new land-fills. There just isn't that much land

Wilson is the electronics theory consultant for ES&T.

available. Add to that the NIMBY (not inmy backyard) attitude, and the problem isvery serious.

If you are an electronics technician, ser-vice center owner, manufacturer or con-sumer, you are in a position to solve thisproblem, as well as the new baby's momnext door. If we're going to survive, weare going to have to stop throwing stuffaway and start fixing things. Further-more, you need to stop encouraging peo-ple to throw things away. This is a prob-lem that must be solved.

Now think about this: when you throwthat AM/FM radio away, you are not onlyhogging up the scenery and using uprapidly diminishing landfill space, youare also helping to use up one of our mostimportant reserves: energy. It takes ener-gy to build a new radio. Furthermore, ittakes metals and chemicals. I know thatthis is going to be a big surprise to manypeople; but, we do not have an endlesssupply of these materials.

Is anyone listening?I remember when tantalum capacitors

first hit the market. There was some con-cern about the fact that the tantalum mightcause a problem with the environment. Abrave parts supplier in my area made avaliant effort to solve the problem. He puta barrel in the corner of his showroomwith a sign asking technicians to throwtheir discarded parts into the barrel when-ever they came to buy parts. There was a

special emphasis on the tantalum capac-itors, paper capacitors and transformers.

Within one week the barrel was half -full of cigarette and cigar stubs, wrappersfrom everything you could imagine.

Is that funny? Where do you supposeall the parts that were supposed to be inthat barrel went? How do you recycle cig-arette stubs?

Let's switch over to the way manufac-turers are contributing to the landfill prob-lem. My friend Frank, owner of a servicebusiness in Arizona, once told me that thegreatest contribution I could make to theconsumer servicing industry was to solvethe parts problem. The shop ownerscouldn't do it. The technicians couldn'tdo it, and the manufacturers couldn't doit. So I guessed I'd better jump in. But Icouldn't solve it either.

What does that have to do with the land-fill problem? Here is a set that has beenwaiting six weeks for a part. The customeris irate. Solution: sell the customer a newset. Give a good trade in allowance. Thensend the old set to diaper heaven.

Some electronic equipment that shouldbe relatively easy to service is being soldin sealed containers. They are notrepairable only because they are sealedand there is no service literature available.More landfill fodder.

Some equipment is being made withabsolutely no servicing informationavailable; not even a schematic. If youdon't believe that, try to get a switching

TRANSMITTER FEEDLINEDUPLEXER

ANDCIRCULATOR

200W -4DB -4DB

ANTENNA

= 200W + 2DB

+10DB

Figure 1. A system consists of a transmitter that has a power output of 200W. a feedline with 4dB loss. a duplexer and circulator with 4dB loss.and an antenna with 10dB gain. What will be the effective radiated power of this system?


TRANSMITTER FEEDLINEDUPLEXER

ANDCIRCULATOR

ANTENNA

120W -5D8 -4DB + 6D13

=120/M - 3D13

Figure 2. A system consists of a transmitter that has a power output of 120W, a feedline with 5dB loss, a cuplexer and circulator with 4dB lossand an antenna with 6dB gain. What will be the effective radiated power of this system.

regulator schematic for a certain popularcomputer. That subassembly has beendeemed by the manufacturer as notrepairable. Now I am talking about prof-it and landfill fodder.

Is there any way out of this mess? Somecompanies make laundry products thathave been selling refills for their bottles.That means that someone knows aboutthe problem besides us. Is there anythingyou can suggest? Let me know. We're allin this together.

Where is my color code?Joe Risse and I have just finished a two -

book series. Those books deal with theFCC and CET tests as well as with otherlicense and certification tests. To get thebooks finished we had to go on fire drillstatus. So I couldn't get the capacitorcolor codes out and I didn't have time torespond to other queries. If you are on thelist of people waiting for something, youwill probably have it by the time you readthis. Sorry about that.

FCC test problemsabout radiated power

Let me introduce you to PhronsieDwitrong. When he graduated from high

school he took a job inspecting buggywhip holders. He also dabbled in radioservice, so he started thinking about him-self as an electronics technician. He evenread some stuff about it in a library book.

After four years he started to lookaround for another job. An ad in the help -wanted section of the paper got his atten-tion. They were looking to hire electron-ics technicians.

When he applied, Phronsie was told hewould need an FCC license and he wouldalso do well to try for a CET rating.

You know that the FCC has publishedall of the questions and answers for the

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GROL (General Radio Operator Li-cense). Phronsie borrowed a copy fromhis former high school shop teacher andspent about two hours looking through thepages. He was sure he was ready, so hetook the test. He wasn't ready. Here is anexample of a question he couldn't answer.

"What is the effective radiated power ofa repeater with 200W transmitter poweroutput, 4dB feedline loss, 4dB circulatorand duplexer loss, and 10dB antenna gain."

Phronsie took a wild guess and missedthe answer by a mile.

The solution(Note: in the FCC problems, the effec-

tive radiated power is referenced to astandard dipole.)

It's too bad that Phronsie didn't sub-scribe to ES&T. By reading this columnhe would know how easy it is to solve thatkind of problem.

Every time the power is increased by1dB, the power is multiplied by 1.259.

As shown in Figure 1, in the systemdescribed in the problem there is an over-all gain of:

-4dB + (-4db) + 10dB = 2dB.So the power will increase to:(200 x 1.259) x 1.259 = 317W.Just remember to multiply the power

by 1.259 as many times as there are 1dBincreases.

All of the FCC problems involve avalue of power that is raised or lowered

by an even number of dB, so this simplemethod can be used for every FCC prob-lem that involves raising or lowering thepower by a number of dB.

When the value of dB is negative, itmeans that there is a lower output powercompared to the input power. In this case,every time the power is decreased by 1dB,the power is divided by 1.259. That ruleis demonstrated in the next problem fromthe FCC pool of questions for GROLexaminations.

"What is the effective radiated powerof a repeater with 120W transmitter out-put power, 5dB feedline loss, 4dB duplex-er and circulator loss and 6dB antennagain? Refer to Figure 2.

Solution to the problemThe overall gain is -3dB. In other

words, there is a 3dB loss. Therefore, thepower is divided by 1.259 three times:

120W/1.259 = 95.3W95.3W/1.259 = 75.7W75.7W/1.259 =60.6WThe FCC answer is 60W.This should come as no surprise to

experienced technicians. It is a well-known rule that reducing power by 3dBcuts the power in half. Also, raising thepower by 3dB doubles the power.

If you use the better value of 1.2589 inthe above calculations, you get 60.1, andthat is significantly closer to the actualone-half power mark.

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Using logarithms to solvethe first problem

If you are a technician who prefers thesolution from a more formal stance, hereis how it goes. The equation is:

dB = 10log(PA/PB)If there is a dB gain, let PB be the start-

ing power and PA be the new (increased)power. If there is a dB loss, let PA be theinitial value of power and Ps be the newreduced power.

In the first problem discussed earlier,there is a dB gain, so PB is the startingpower (200W) and PA is the new power.Then

2dB = I Olog(PA/PB)

Divide both sides of the equation by 10;

0.2 = log(PA/200)

Take the antilog (log -1) of both sides ofthe equation;

log -1(0.2) = log-i[log(PA/200)]

1.584893192 = PA/200

PA = 1.584893192 X 200 = 316.97.Rounded off to three places that becomes317W.

Using logs to solve

the second problemIn the second problem, there is a 3dB

loss. So PA is the starting power (120W)and pB is the new power.

3dB = 10log(120/PB)

Divide both sides by 10

0.3 = log(120/PB)

Take the antilog of both sides

1.995 = 120/PB

Rearrange to get PB alone on one sideof the equation

Ps = 120/1.995 = 60 (approximately)

The truth is that decreasing a power by3dB does not exactly divide the power by2. Likewise, increasing the power by 3dBdoes not exactly double power. Thoserules give a good approximation and theyare used by the FCC to get answers to theirproblems.


Business Corner

TQM Point 10Eliminate slogans, exhortations and

targets for the work force asking for zerodefects and new levels of productivity.Recently, I visited a human resourcesoffice to discuss some possible technolo-gy purchases. As I talked with the officemanager about her needs, I noted that shehad placed several humorous "team-work" posters around the office. One ofthe posters said something like "Let's allpull together" and showed cartoon char-acters participating in a tug-of-war.Another advised that "Square Pegs Don'tFit" and displayed a character attemptingto hammer a square peg into a round hole.

While each poster made an obviouspoint about teamwork, each also gave animplicit message about conforming to theneeds of the organization. Certainly, orga-nizations that have employees workingand pulling together or where all employ-ees follow the organizational missionshould succeed.

Slogans can be counterproductive

The logic behind these posters andother organizational slogans makesDeming's tenth point about slogans, zerodefects, and productivity goals seem con-tradictory. However, Deming understoodthat the use of slogans and exhortationscould damage employee morale andimpede organizational success.

Many times, employees who alreadyexceed both qualitative and quantitativeproduction goals and who already workas teams may find those slogans insult-ing. Indeed, the posters displayed in the

Ross is a technical writer and microcomputer consultantfor Ft. Hays State University, Hays, KS.

Will Total QualityManagement

Work For You?Part 10

human resources office only ask for moreteamwork, production, and conformance,and imply that laziness or an uncoopera-tive attitude exists. None of the postersrecognized continuing excellence.

Rather than make slogans, productivi-ty, and quotas the sole focus of the orga-nization, Deming advises us to takeanother look at the various processes thatmake up work and production. The use ofmotivational slogans and the setting ofnumerical production goals solelyemphasizes the power of managementinstead of the needed cooperationbetween management and employees. Inaddition, that emphasis implies that adivision exists between managers andemployees. Managers set the goals;employees reach the goals.

Employee empowerment

When employees are empowered, thesituation changes. Organizational goal -setting requires the recognition thatpower exists not only in the hands of man-agement but also in the hands of theemployees. While managers must remainaware of potential budgetary problems,possible personnel conflicts, and marketchanges, employees have an acute aware-ness about working conditions, equip-ment needs, and morale problems. Thus,the recognition of existing power in bothcamps also requires a balancing andmerging of the power interests.

Because of this sharing of power andknowledge, it makes sense for manage-ment to consult with employees aboutmethods for improving organizationalefficiency and production. Instead of ask-ing employees to perform better with lessor the same resources, managers shoulduse their budgetary, personnel, market

By John A. Ross

knowledge, and, most of all, their listen-ing skills to ensure that resources go tothe proper areas and that the talents of per-sonnel match their responsibilities.

The empowerment of employees alsoplaces an obligation on them. Whileemployees have the duty to tell manage-ment about possible improvements inworking conditions and equipment, theyalso are obligated to keep from using theirknowledge for the purposes of manipu-lating management for their own ends.

Integrating personaland organizational goals

All this points toward the integration ofpersonal goals with organizational goals.Yet, this integration acquires a deepermeaning when we examine all the poten-tial conflicts and consequences of goalsetting and decision making. Both typesof goal -setting, organizational and per-sonal, may concentrate on efficiency,effectiveness, accountability and proce-dures, because the goal -setters assumethat those characteristics are best for theorganization and are what the ownershipdesires from its employees.

However, true organizational successdepends on the understanding that goal -setting should revolve around both thecharacteristics of production and aroundprinciples such as honesty, equality, fair-ness, justice, and the protection of indi-vidual rights. Without the merging ofthose characteristics and principles, theorganization and the individuals thatmake up the organization will encountergoal conflicts and will never achieve truesuccess. With the merging of those char-acteristics and principles, the growingtrust between departments and individu-als will guide the organization to success.

July 1994 Efectronk Servicing & Technology 59

Video Corner

Additive vs subtractive colorsRoger I). Redden

If you have worked on color TVs forquite a while, you may have had a conver-sation with a customer that was somewhatlike this one.

Technician: "I'm sorry, but the problemwith your TV is a bad picture tube. Theblue gun in the picture tube isn't working."

Customer: "I thought that when the pic-ture tube went out there was no picture atall. And what's a blue gun?"

Technician: "There are three electronguns in the picture tube. One gun lightsup red phosphors, one green phosphors,and one blue phosphors. The proper mix-ture of light from these phosphors givesyour TV's screen the normal colors. Mypicture tube checker shows that the bluegun in your tube is not working."

Customer: "OK, so that's why my pic-ture has no blue. But why does everythinglook yellowish?"

Technician: "Without blue, there's only

Redden is owner and operator of a consumer electronicsservice center.

red and green. Red and green mixed to-gether makes yellow."

Customer: "That's not right. I paint asa hobby, and I know that if you mix redand green together you don't get yellow,you get some shade of brown."

Technician (reaching back in the mistypart of his memory to find something use-ful): "I'm sure you're right about mixingpaint, but paint colors are subtractive col-ors, while colors from light are additive."

Customer: "I don't understand. Couldyou explain that to me?"

Technician (lamely, after finding onlyfog in the misty part of his memory thistime): "That's just the way it works."

The fog encountered by the technicianmay not be his memory's fault. Sinceknowledge of subtractive colors is notneeded to service color TVs, many of thebooks and courses, at least the older ones,that explain the operation of color TV,mention additive and subtractive colors,but either give no explanation of subtrac-tive colors, or give only a very brief one.

The following explanation might havehelped the technician talk to his customerabout subtractive colors.

A review of color visionThe most popular theory of how our

eyes sense color is the Young -Helmholtztheory. According to this theory, three dif-ferent groups of cones (light sensitivecells) in our eyes respond to a range of fre-quencies centered on the frequencies wesee as red, green and blue. The frequencyresponses of the groups of cones overlapeach other to varying extents, but eachgroup responds most strongly to a partic-ular range of frequencies that encompassone of those three colors. This overlappingresponse of the different groups of conesmay be why we perceive either a singlefrequency or a mixture of two widely sep-arate frequencies as the same color.

Figure 1 illustrates the idea of how wemight see the color yellow when our eyesare exposed either to one frequency, or toa mixture of a red and a green frequency.

A SINGLE FREQUENCY CAUSINGAN EQUAL RESPONSE FROM BOTHTHE RED AND THE GREEN CONES

IN THE EYE; SEEN AS YELLOWTWO FREQUENCIES CAUSING

EQUAL RESPONSES, RESPECTIVELYFROM THE RED AND THE GREEN

CONES IN THE EYE; SEEN AS YELLOW

VIOLET BLUE CYAN GREEN YELLOW RED

Figure 1. This is a drawing showing hypothetical response curves of the red, green and blue cones of the eye, and how two frequencies causingequal responses, respectively, from the red and the green cones might be seen as the same color as one frequency causing an equal responsefrom both groups of cones.


VIOLET BLUE CYAN GREEN YEL_OW ORANGE RED

400 455 490

WAVELENGTHS IN NANOMETERS

550 580 620 700

Figure 2. A rough sketch of the placement of colors in the spectrum of visible light, with wavelengths given in manometers, or billionths of a meter.

The actual response of the cones of theeye is different from that shown in Figure1; more complex, and apparently not alto-gether understood.

Compared to the vast range of electro-magnetic frequencies that exist, our eyesrespond to a relatively narrow band of fre-quencies between about 428 million MHzand 750 million MHz: a bandwidth of 272million MHz, or 272 x 1012.

The spectrum, or range, of visible lightis normally shown using the wavelengthsof the light, not the frequencies. This isthe way it is shown in Figure 2, which is

a rough graph of the visible spectrumshowing the approximate positions ofred, green, blue, yellow and cyan on thespectrum. Magenta is not shown becauseit does not occur as a single frequency inthe spectrum, but only as a mixture of redand blue, colors taken from nearly oppo-site ends of the spectrum.

Mixing additive colorsAfter that brief review of how we see

color, let's look at additive color mixing,the operation that TV technicians dealwith daily.

Figure 3. Any two primary additive colors adjacent to each other on the inside circle add toproduce the color between them on the outside circle. Any two primary subtractive colorsadjacent to each other on the outside circle subtract to produce the colors between them on theinside circle.

The essential fact about additive colorsis that the sources of additive colors emit(or in special cases reflect) light, but donot absorb it. Thus, when we mix two add-itive colors together, neither absorbs anyof the color supplied by the other.

For example, red light mixed withgreen light results in light containing boththe original colors. Our eyes receive thesecolors and see the combination as if itwere the single color yellow. In the samemanner, our eyes perceive a mixture ofgreen and blue as the color cyan, or a mix-ture of blue and red light as magenta.

As technicians, we know that the prop-er mixture of red, green and blue additivelight produces white light; what we strivefor when we adjust the screen or drive con-trols in a color TV for gray scale tracking.

Mixing subtractive colorsA subtractive color is usually produced

by light reflected from the surface of anobject. But while the surface of the objectreflects some of the frequencies of thelight which strike it, it absorbs the otherfrequencies which strike it. For example,a red surface strongly reflects a band offrequencies we see as red, probably weak-ly reflects a range of frequencies on bothsides of the red frequencies, and absorbsall other frequencies.

A subtractive color can also be pro-duced by a color filter, such as one usedin a camera. Such filters absorb some fre-quencies and transmit, or pass, other fre-quencies of light. A blue filter, for exam-ple, transmits blue light while it absorbs(blocks) light of other colors.

To mix subtractive colors, we mustkeep in mind what each source absorbs aswell as what it reflects, or, in the case offilters, transmits.

Seeing what is absorbed and what isreflected is easier using the primary sub -


PRIMARYADDITIVECOLORS

RED

GREEN

GREEN -66.

BLUE 20"

\21k,BLUE

RED

PRIMARYSUBTRACTIVE

COLORS

YELLOW

CYAN

MAGENTA

RED ABSORBS BLUEGREEN + GREEN = GREEN

0 BLUE ABSORBS RED

GREEN ABSORBS REDBLUE + BLUE = BLUERED ABSORBS GREEN

GREEN ABSORBS BLUEMo. RED + RED = RED

BLUE ABSORBS GREEN

Figure 4. Starting at the left of the figure, light sources are added to produce secondary additive colors. The colors obtained, shown between dot-ted lines, are the primary subtractive colors. These primary subtractive colors combine with each other to reflect the colors after the equal signs.

tractive colors. Figure 3 shows that theprimary subtractive colors are the oneswe get when we mix the primary additivecolors. For instance, a mixture of red andblue light produces magenta, which is aprimary subtractive color. As the figureshows, the other primary subtractive col-ors are cyan and yellow; colors obtainedby mixing green with blue and red withgreen when using the additive colors.

Figure 4 shows the primary additivecolors mixed to form the primary subtrac-tive colors. These colors in turn are mixedagain to form red, green and blue. But inthe second mixing, the mixing of sub-tractive colors, light is being absorbed.

When we mix the yellow with the cyan,the green that results reflects less totallight than the yellow and cyan would re-flect if they were unmixed. This is be-cause the red light contained in the yel-low absorbs the blue light from the cyan,

and the blue light contained in the cyanabsorbs the red light from the yellow.

What color results when we mix allthree of the primary subtractive colors-yellow, cyan and magenta-together?These three primary subtractive colors,mixed together in the proper proportions,become black. A black surface absorbsall the light striking it; it reflects no light.

To see why no light is reflected, lookcarefully at Figure 4. We started on theleft with two units of red, two units ofgreen and two units of blue. In the processof mixing the yellow, cyan and magentawith each other, two units of red, two unitsof green and two units of blue were ab-sorbed. Since the mixture absorbs all ofthe light energy striking it, none is reflect-ed, and the surface appears black.

In the end, it's black and whiteIn color mixing, the terms additive and

ES&T READER SURVEYBound into this issue is the ES&T Reader Survey card. It's located onpage 31.

It's a mini survey about you. We would like to hear about the problems youface, the opportunities you see and the equipment you use during the courseof your work day.

The postage is paid. All you have to do is fill it out and mail it.

What could be easier?

Please fill yours out and mail it today.

subtractive are very meaningful. Additivecolors mixed together become brighter,and the right frequencies in the right pro-portions produce white light. Light hasbeen added to light. In contrast, subtrac-tive colors mixed together become dim-mer, and the right frequencies in the rightproportions produce a black surface. Lighthas been subtracted from light.

Instant replayNow that we know more about addi-

tive and subtractive colors, let's put thetechnician back in our original scene,right after he says paint colors are sub-tractive while colors from light are addi-tive, and the customer asks, "Could youexplain that to me?"

Technician: "When the phosphors in theTV give off light, all of the red and all ofthe green color is emitted and we see themixture as yellow. But subtractive colors,such as the pigments in paint, don't pro-duce light, they just reflect some of it andabsorb some of it. When you mix red andgreen paint, the red paint absorbs most ofthe green light that hits it. At the same time,the green paint absorbs most of the redlight that hits it. The small amount of lightstill reflected appears to be brown."

Customer: "I'll ask my art instructorabout your explanation of color. But fornow, I want you to show on that checkerof yours how you know my picture tubeis bad."

Which shows that even when you'reright, you can't convince some of the peo-ple some of the time.


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pressors is now available from ShapeElectronics. With 30 models in the line,they provide surge protection for all typesof electronic equipment used in the officeor at home.

Four grades of surge suppressor mod-els are available. Premium -grade modelsoffer a lifetime product and equipment

warranty. They protect PCs and worksta-tions used for data and word processingapplications. Heavy-duty premium -gradeunits are applicable in test equipment,copy machines, and laser printers. Com-puter -grade models protect personal com-puter systems against power surge andnoise protection for home computers,home entertainment, and appliance appli-cations.


Aerosol, non-CFC contact cleanerPrecision Cleaner II, a non-flammable,

non-CFC, aerosol type contact cleaner, isbeing introduced by Micro Care Corp.

Non-toxic and plastic safe, this newformulation may be used in every indus-try to remove oils, grease, grime, dust,and general contaminants from precisionelectronic and mechanical assemblies. Itgently cleans circuit boards, motors,switches, and other essentials in a varietyof manufacturing, repair, testing, re-search. and medical environments.

This solvent is believed by the manu-facturer to be the only commercially

available non-CFC contact cleaner thatcan effectively replace the use of CFC-113. It is non-conductive, will not burn,will not attack plastics, and cannot harmoperating machinery.

The basic composition the cleaner in-corporates is a new solvent derived fromthe perfluorocarbon family, plus HFCpropellants and some minor additives.EPA approval of the product has beenfiled through the "Significant New Alter-natives Program."



PhotofactThese Photofact folders for TV receivers andother equipment have been released byHoward W. Sams & Co. forJune and July 1994.

JUNE

GECTC 1 77AF 3339TX825TD 333113GP2I0F04 333125GT520FEI 333925GT522FE1 3339

JVCAV-20BM4 3341AV-20CM4 3341C-20BL3 3333C-20CL3 3333C-20RL3 3333C-20WL3 3333

MAGNAVOXCS4537A4 3336CS4538P4 3336CS4540A4 3336RS2555A4 3336RS2565B4 3336RS2568C4 3336RS3182 C402 3328VR96 1 OATO I (sim. to) VCR -253VR9614ATO I (sim. to) VCR -253VR9622AT01 (sim. to) VCR -253XS3182 C401 332825Y105 333631Z101-00BB 3328

PANASONICAEDP226 3332CT-F29L3 3332CT-F29L3L 3332CT-F29L3V 3332CT-27SFIOR 3332PC-29SFIOR 3332PV -2700B VCR -253PV -2700B -K VCR -253PV -2700R VCR -253PV -2700R -K VCR -253PV -2700W VCR -253PV -2700W -K VCR -253YAEDP226 3332

PHILCOP132ORC101 3338VT8720ATO I (sim. to) VCR -253I 3S401 3338

QUASARVH5270 (sim. to) VCR -253VH5270-K (sim. to) VCR -253

RCACTCI69BF 3330CTC169BF2 3330CTC169BG 3330

CTC169BG2 3330 685-0739 3350CTCI69BG5 3330 685-2307-00 3350CTC177AD 3337 2307 3350CTC177AE 3337CTC I77AF 3337 JVC

CTC 1 77AG 3337 C-20BL4 3344

F25251WNFE I 3337 C-20CL4 3344

F2525 I WNJX I 3337 C-20WL4 3344

F2565IBLFEI 3337 MAGNAVOXF2565 I BLJX I 3337 HD2038C203 3352F2625 I ETFEI 3337 RS2002W202 3352F2663ISEFE I 3337 RS2050W202 3352F2663 1 SEJX1 3337 RS2080C205 3352F26633SEFE1 3337 20S105 3352F35100STNMI 3330 VR9710ATO I (sim. to) VCR -254F35100STNM2 3330 VR9720ATO I (sim. to) VCR -254F35750STFM I 3330 VR9722AT0I (sim. to) VCR -254F35750STJ X I 3330 XS2080C203 3352G2534I WKKFI 3337G2534I WKCX1 3337 PANASONICG2666 I CKCX I 3337 ASDP215 335 IG2666I CKKFI 3337 CT-IORIIS 3351G26681 CKKF I 3337 CT -10R1 ICS 3351G26683CKCX1 3337 YASDP215 3351

SHARP PHILCO20E -S110 3329 VT3010ATO I (sim. to) VCR -25420E -S130 3329 VT3020ATO1 (sim. to) VCR -254

SYLVANIA QUASAR20Y100 3340 A DC225 3354

SRC20214 3340 AMEDC2 18 3346VC8922AT0 I (sim. to) VCR -253 QC-20T15J 3354

SX2754HK 3346TOSHIBA TPI915HJ 3354CFI3C20 3334 TP1915J 3354CF26C30 3335 YADC225 3354CF27C30 3335TAC9350 3335 SHARP

TAC9360 3335 SN3 1 3345

TAC9365 3335 25E-MI00 3345

TAC937 1 3334 25E -M120 3345

TV28C30 3335 27E -S50 335527E -S100 3355

JULY 27E-SI20 3355

CROSLEY SONYCT2725C101 3349 KV-20TS50 3347CT2725C102 3349 KV-27XBR26 3342275102 3349 KV-27XBR36 3342

SCC-F I 6H -A 3342GE SCC-F I 6K -A 3342TX82TB 3343 SCC-FI 7H -A 3342I3GP21 I F03 3343 SCC-F I7K-A 334213GP239CO3 3343 SCC-F78G-A 334713GP239F03 3343 SCC-F79F-A 334713GP2400O3 334313GP240F03 3343 SYLVANIA

VC4010ATO I VCR -254GOLDSTAR VC4020ATO I VCR -254GCT2064S 3353 VC4024ATO I (sim. to) VCR -254NC -37A 3353

TOSHIBAJC PENNEY CFI9C20 3348NC -36A 3350 TAC9370 3348


Troubleshooting Tip

TT0394By Roger D. Redden

Emerson Model ECR2100: Sams 2547-1No audio, no video, HV rush heard

When this set was turned on, it pro-duced a rushing sound of HV, but therewas no audio, and the screen remaineddark. When either the channel up or chan-nel down button was pressed, the chan-nels, as indicated by the LED display,changed continuously.

Although the screen was blank, when Iturned the set off I thought I saw, just foran instant, a horizontal line across the cen-ter of the screen. Since the brightness andcontrast controls were already turned tomaximum brightness, I noted the positionof the screen control (so I could reset itlater. After turning the set back on, I slow -

Redden is owner and operator of a consumer electronicsservice center.

ly turned the screen control up and a hor-izontal line appeared.

I had recently replaced bad vertical out-put ICs in two similar Emerson chassis.Was this number three?

The voltage at pin 1 of IC401, the pow-er input to the vertical output IC. was OV,instead of the normal 9V. The resistancereading to ground from pin 1 was about6052; abnormally low. Normal resistanceis about 28052. Was it really as easy asanother bad vertical IC?

Not this time. After I removed the sol-der from around pin 1 of IC401 and againmeasured the resistance from this point toground, I found that the resistance thatcaused the low ohmmeter reading was notthe resistance from the pin of the IC, butfrom the foil to which the pin was sol-dered. This foil leads to R413. The resis-tance to ground from the lead of R413away from pin 1 was 56g. When I fol-

lowed the path toward the power supply,as shown on the schematic, it led me toR443, a 565I resistor.

Hmm. The ohmmeter showed 560 toground and here was a 5652 resistor. Wasthis a coincidence, or was there a short onthe other side of that resistor where it con-nected to pin 1 of IC402, the 9V regula-tor. When I measured the resistance at pin1, it indeed measured Oa The only com-ponents at that point that should be ableto cause a dead short were IC402 or C430.

A short at pin 1 of IC402 would havecaused excessive current, that might havedamaged D408 or 8442. When I checkedthese components, D408 checked good,but R442 was open.

I touched my ohmmeter probe back topin 1 of IC402. At least a dead short in acircuit with only two suspects should beeasy to find. Unfortunately, the resistancereadings were bouncing up and down.

PART OFFB401 (IHVT)

D408

O

11.8V

R44210U1W

C430T2200 ,,F

R46110SI

R4435651

IC4029V REG

T I

IC401VERT OUT

11.2V

F9 OV(A)

1-71 9.0V(13)

R4134.711

C412330,,F

9.0V(A)


BooksMastering Radio Frequency Circuits

through Projects and Experiments, ByJoseph J. Carr, TAB Books, 304 pages,ISO illus., $29.95 paperback, $37.95hardcover.

Mastering Radio Frequency Circuitsthrough Projects and Experiments, an entryin the TAB Mastering Electronics Series, ispacked with hands-on bench experimentsand projects readers can do. Students,beginning- and intermediate -level elec-tronics hobbyists, ham radio operators andshortwave listeners will be particularlyinterested in this book by Joseph J. Carr.

Readers will learn how to design andbuild their own RF amplifiers, simple wireantennas, microwave integrated circuits,and receiver preselectors. They'll discoverhow to wind their own RF coils and trans-formers, repair fixed and variable capaci-tors, and build radio receiver circuits andbridges. Two especially illuminating anduseful projects involve spectrum analyzersand time domain reflectors.

Carr is an electrical engineer and authorof numerous technical articles and elec-tronics books. He is a regular columnist forseveral electronics magazines, and hasreceived awards for his knowledge andexpertise in the field of electronics.

TAB Books/McGraw-Hill, Inc.. Blue Ridge Summit.PA 17294-085(1

Servicing PC -Based Equipment, ByDon D. Doerr, Prentice Hall, 384 pages,$26.95 paperback.

Based on more than ten years experience,Don D. Doerr shows you how to servicePC based equipment quickly and easily.The book is an indispensable source fordiagnosing PC problems. Flow charts takeyou step-by-step through the troubleshoot-ing procedure, until the problem is isolat-ed. Troubleshooting tips help you solveproblems without needing to send parts outfor costly repair service. You learn howsimple it is to protect and recover dataquickly and easily. Doerr shows how tolocate the best sources for parts, diagnos-tics, schematics and board repair. The mostcommon questions asked by service tech-nicians are covered.

This book features a DOS referenceguide and a list of recommended utilitiesand step-by-step instructions for repairingand installing a hard disk. The book con-tains sections about common diagnosticsoftware, boards and drives, system boards,expansion bus, diagnostic and post errorcodes, hard drives, floppy drives, monitorsand keyboards, power supplies and power

protection, automatic test equipment types,soldering equipment, fault isolation guides,and switch and jumper settings. It also con-tains the most frequently referenced serviceinformation. The book devotes a full chap-ter to buying a new PC. Servicing PC -Based Equipment features special refer-ence sections on opportunities in theservice industry, a vendor support list, aglossary, and complete index.

Prentice Hall, Paramount Publishing EducationGroup. Englewood Cliffs, NJ 07632

McGraw-Hill Circuit Encyclopediaand Troubleshooting Guide, Volume 2,By John D. Lenk, McGraw-Hill, 691pages, $59.50.

The second and concluding volume of acompilation of information on electroniccircuits, the McGraw-Hill Circuit Guide,Volume 2, features detailed material anddata on hundreds of circuits commonlyused in all phases of electronics.

Expanding on the well -received first vol-ume (published in June, 1993), this note-worthy reference not only focuses on 700additional integrated and discrete -compo-nent circuits, but also contains a wealth ofnew test and troubleshooting data. It

explains how circuits operate and wherethey fit into electronic equipment and sys-tems, groups all of the circuits by function,and gives a specific troubleshootingapproach for each type of circuit.

With more than 750 detailed illustrationsand schematic drawings, the reference sup-plies proven component values for actualcircuits, gives sources and mailing address-es for each, and includes substitution andcross-reference tables to help locate sub-stitute ICs. The book is designed so that thecircuits can be put to work immediately orthe circuit values can be easily changed tosuit particular requirements.

A resource for engineers, technicians,and hobbyists, Volume 2 of this Encyclo-pedia covers many different types of cir-cuits: audio -frequency, basic amplifier, RFand IF, special-purpose, power-supply/lin-ear-regulator, battery -power and microp-ower, and power -processing. In addition, itexamines classic op -amp, OTA and Nortonamplifier, temperature indicator/controller,transducer/signal-conditioner, and com-parator circuits.

Lenk has been a technical writer spe-cializing in practical troubleshootingguides. He is the author of more than 75books on electronics.

McGraw-Hill. Inc.. Professional Book Group,New York. NY 10011

Tips (Continued)

I found that pressure on the circuitboard would keep the short present. I sus-pected that there might be a solder -splashshort on a trace from pin I of IC402, buteven with the help of a magnifying glassI was not able to see one. Could there bea foreign object on the top of the boardcausing an intermittent short?

I carefully followed the path of the tracefrom pin I of IC402 on the bottom of theboard, relating that path to the top of theboard. I couldn't spot any foreign objects.But the path of the trace passed justbeneath the antenna coax plug-in to thetuner, and R46I was located there, mount-ed high off the board. One of its leadsappeared to touch the metal plug-in of thecoax. Wiggling 8461 slightly made theshort come and go.

I resoldered R461 closer to the boardso its leads could not touch the metal plug-in, and replaced R442. This returned theset to normal operation.

When R442 became open, this discon-nected supply voltages to the video if andsound if circuits, as well as other circuits.Absence of supply voltages to several cir-

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Mail AllCorrespondence To:

Electronic Servicing &Technology

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ClassifiedClassified advertising is available by the word or per column inch.By -the word. $1.65 per word, per insertion, pre -paid Minimum charge is $35 per insertion. Initials and abbre-viations count as full words. Indicate free category heading (For Sale, Business Opportunities, Miscellaneous,Wanted). Blind ads (replies sent to ES&T for forwarding) are $40 additional. No agency discounts are allowedfor classified advertising by the word. Contact Linda Romanello at 516-681-2922 to place your classified ad(by -the -word). Mastercard, VISA, American Express and Discover are accepted for FAX or mail orders.Per column Inch (classified Display): $235 per column inch, per insertion, with frequency discounts avail-able, 1" minimum, billed at 1/4" increments after that 10" maximum per ad. Blind ads are $40 addition. ReaderService Number $25 additional to cover processing and handling costs. (Free to 4 -inch or larger ads.) Formore information regarding classified display advertising please call 516-681-2922. Optional color (deter-mined by magazine) $150 additional per insertion.

Send your order, materials and payments to:Electronic Servicing & Technology, 76 North Broadway, Hicksville, New York 11801

Attn: Linda RomanelloPhone: 516-681-2922 FAX: 516-681-2926

FOR SALE

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Quantum Data 801C Color Character Generator$495. Tektronix & Philips scopes with TV Triggeravailable. We buy surplus equipment. Call/fax orwrite Test Equipment Sales, P.O. Box 986,Londonderry, NH 03053-0986, Phone/fax (603)434-2544.

FOR SALE

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Sencore Equipment for Computer Monitor RepairBusiness. Also Schematics and Database. Excel -lent potential for technical individual. Limitedfinancing. Information: (800) 979-1969 Days.

REDUCED 85%. Diehl Mark III $69, Diehl Mark VHorizontal circuit tester $179. New. Conductivecoating for remote control keypads $9.99 ppd.WEEC, 2411 Nob Hill Road, Madison, WI 53713.608-238-4629, 608-233-9741.

FOR SALE

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ClassifiedTEST EQUIPMENT BOUGHT & SOLD: OSCIL-LOSCOPES, ETC. 1-408-738-4206. FAX 1-408-736-6946.

SENCORE ELECTRONIC TESTING EQUIP-MENT. Excellent condition, hardly used. SC3080Waveform Analyzer System with 50 to 1 HV probe,$2700.00; VA62A Video Analyzer, $2800.00;PR57 Variable Isolation Transformer, $450.00; orwhole package for $5500.00 Cdn 1-604-748-6188, Vancouver Island, Canada.

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Sencore VC93 VCR Analyzer, Sencore VA62ATV Video Analyzer, Sencore PR57 VariableIsolation XFMR 18 months old with 18 months war-ranty remaining. AHNTECH, 619-371-4501 Denisor Don.

Earn SSS Repairing Zenith TV's to componentlevel-now over 1000 models 1983-1993.Guaranteed effective and reliable cost cuttingsymptom/cure format. Buy manual and receiveFREE report, "Repair Shorted CRT's Fast" (rasterone color) $89.95. Demo Sampler $19.95. ZMEX,807 Queen Palm Lane, Sarasota, FL 34243.

SERVICE DATA & HARD TO FIND PARTS pre-viously -owned SAMs, manufacturers data, books,FREE catalog. AG Tannenbaum, Box 110, E.Rockaway, NY 11518. 516-887-0057, Fax 516-599-6523.

BUSINESS OPPORTUNITIES

Super Career opportunity! Will lease profitablecon sumer electronics service shop for as high as70% lessee/30% lessor labor split. All building andutility overhead is paid by lessor. Only experiencedtechnicians who are self -motivators need apply.Income potential is limited only by individuals per-sonal skills. Contact KEMPCO ELECTRONICS,223 E. Main, Grangeville, Idaho 83530. Phone 208-983-0429.

MOVE TO THE LARGEST REPAIR PROFITMARKET IN THE COUNTRY - SUNNY SOUTHFLORIDA Think about it, our clients bring theirREPAIRS & MONEY from all parts of the world.Annual Gross 375,000k, take home 80 - 95,000k.Owner retiring, Fully staffed & operated in thelargest growth area of Ft. Lauderdale. Established12 years. No competition. Authorized 15 majorbrands. Totally computerized. Simple to operateBusiness. Price is 150,000k, Owner financingavailable. (305) 474-2677.

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MISCELLANEOUS

A.T.S. SPECIALTY REPAIR PRODUCTS for VCRand copier type equipment. Products includeINSTA-PLASTIK GEAR AND PLASTIC REPAIR.Proven in over 3000 service centers, INSTA-P LAS-TIK field repairs broken parts, nylon gearsand teeth. (800) 343-3530.

Readers' ExchangeReaders' Exchange has been reinstated as a Ire:

service.The following restrictions apply to Readers.

Exchange: Only individual readers may use Readers'

Exchange, and items must be restricted to thosethat are ordinarily associated with consumer elect Rinks as a business or hobby. If you're in busi-ness to sell the item(s) you want to offer for sale.the appropriate place for your message is in a paidadvertisement, not Readers' Exchange.

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All submissions must be typed or printedclearly!

Send your Readers' Exchange submissions to:

Readers' ExchangeElectronic Servicing &

Technology76 N. Broadway

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WANTED

Sams VCR Facts or VCR Service Literatureone or one hundred. Dales, Rt. 1, Box 236,Mtn. View MO 65548.

Used Flyback for a 19 inch RCA/GE TVchassis CTC136AC. Part no. 175297 (Sams2658). Rays TV, 4821 East View Drive, NewOrleans, LA 70125-4413.

Sencore YF33 Ringer-Yoke/Flyback tester.DJ's TV -VCR Repair, 340 N. Arcade,Gladwin, MI 48624. 517-426-2027.

I'd like to purchase 1 qty. B&K 1050. Pleasephone your offer. Attn. IVO on 403-539-4240, or fax 403-539-5717.

Ilorizontal Stat Control for Sony TV ModelKV1953RS. B&B Electronic Service, 2230N. 55th Ave. Holly, FL 33021 or call 305-987-5235.

New or used Mitsubishi Fly 334P09403Model CK2582. Will pay. Dales, Rt. 1, Box236, Mtn. View MO. 65548.

Instruction manual for a B&K transistortester Model 510. (copy o.k.). Ray's TV,4821 East View Drive, New Orleans LA,701254413.

Schematic for Panasonic CT -1110D Chs.NMX-K9D Flyback, PanasonicTLF6041F, Sony Pix tube 400EDB22.Keith Zarin, Keith's TV Service 7233Centreville Rd., Manassas, VA 22111, 703-368-1300, Fax 703-368-8637.

Need Dest PC Scanner Interface Card and24V/500ma power pack or source of sup-ply for these Dest PC 1000 to 3000 seriesitems. stationed in Germany. Call 011-49-6561-18830, Alan Young, 611 Ord. CO.,PSC 12 Box 570, APO AE 09156.

Complete chassis (less picture tube) forSony Model KVI9TR20 S/N 8024214 19inch color TV . George J. Demaris, 7387Pershing Ave., Orlando, FL 32822, 407-277-3746.

Deflection yoke or tube assembly with yokefora Mitsuba CM48U VGA computer mon-itor. Also looking for 1976 Pioneer ModelSX- I 250 stereo receiver working or notworking but must be in good condition.Contact Frank, 516-669-0283.

Clock for Zenith radio Model # F472W3,clock # D163EN Digital 100 by GeneralTime Corp., Armin Kupfer, 1-313-675-2798.

S/M or schematics to buy or borrow forKensonic Accuphase E-202 amp, for refer-ence 240R (by Quadraflex) receiver and forPioneer CT -7R cassette deck. ContactRichard Sereda, College of San Mateo,1700 W Hillsdale, San Mateo, CA 94402.

Flyback Transformer wanted for a Midlandtelevision receiver, Model #15-109B. PaulCapito, 137 West 21 St., Erie, PA 16502.

Samsung VCR Model #VR2650, IC -0601NEC #D75116CW, IC -0501 LA7096, RCAVCR Model #VR301, IC -201, Samsung#HD49748NT cassette door and spring.'John's Repair Center 142 Jackson St.,Phila., PA 19148. Ask for John Carr


Readers' ExchangeVCR service manual for Goldstar GHV-1233M. Will purchase or copy and return.Anchor VCR & TV Repair, 5890 WashburnWay, Klamath Falls, OR 97603, 503-884-5985.

Need Zenith part #861-640 wheel gear,worm for VCR model VR5000. Not avail-able from Zenith. Will pay good marketprice. Bing Huie, PO Box 2634, Alameda,CA 94501, 510-523-9087.

Schematic for AT&T cordless phone,Model 4600. Would like to have a copy ofonly the Handset. CKT or PB: 846238103Issue 3, Rev. "F." Will pay for copy &postage. Raul M.G., 9925 Audobon St., ElPaso, TX 79924, 915-751-6833.

Five inch color TV tube, new or used,Model # 150AYB22 (B) (Hitachi). GeorgeDemaris, 7387 Pershing Ave., Orlando, FL32822, 407-277-3746.

Manual wanted for Century Model FC-2tube tester. Contact Bill Ettlich, 916-677-1998.

FOR SALE

Tektronix 454 Oscilloscope. 150MHz, dualtrace, delayed sweep, small compact size,including owners manual and 1 probe,$425.00. Frank, 516-669-0283.

One MN158461 VAA2 four -bit micro-processor, one Zenith 905-926 MOS. IC,M50442-522 Mos. IC. Contact John'sRepair Center, 142 Jackson St.,Philadelphia, PA 19148.

Service manuals: AMS 7XX-2XXX, Fisher(TV, stereo), Superscope, Hitachi (TV),Mitsubishi (TV, stereo), GE (TV, VCR),Zenith (TV). $15.00/box or $175.00 all plusshipping. Covers years 19XX-1988.Raymond Ellsworth, 111 Long Lake Ave.,Alpena, M149707, 517-354-5636.

Old editions of Electronic Servicing &Technology from Jan. 1973 -Dec. 1993.Also, TekFax 110, 112, 114. No reasonableoffer will be refused. Bing Huie, PO Box2634, Alameda, CA 94501, 510-523-9087.

Sencore CR70 like new 625.00, one Mark12 Mezzer Field Strength meter with case$49.00, one McGraw Edison FM signalgenerator 25-960MHz. $199.00. Call after6 pm. Al Nikora Sr., 5298 Argyle Ct.,Sterling Hgts. MI 48310, 313-268-6938.

Sencore VA62A & VC63 in original box$1500.00 plus UPS> A.G. Tannenbaum,PO Box 110, E. Rockaway, NY 11518 516-887-0057.

Conar solid-state scope $125.00, B&K TVanalyst W/new part $100.00, Conar TV pat-tern generator $45.00, Magnavox color TVtest fixture 19 inch CRT w/adaptors $65.00.Neville Young, 214 E. Robertson St.,Brandon, FL, 33511, 813-685-1900.

Info for a federal telephone and telegraphtype 61 radio also Sony TC377 reel to reeltape recorder. Have many Rider manuals tosell and sound powered phones -new.Contact Robert Haan, 2885 E. BeltlineN.E., Grand Rapids, MI 49505.

Sencore SC60, SC61, PR57, VA62, ormore, probes & manuals all in good condi-tion. Must sell, best offer. TeeVax, PatMontague, 422 Wilson St., Santa Rosa, CA95401, 707-545-1195, Fax 707-545-1227.

Viejo VCR courses-Microfiche-Tubes-Sams-VCR/TV/audio/misc. ser-vice manuals etc. SASE for list. G.K.Ketchem, 1849 Crooked Pine Dr., #C-5,Surfside Beach, SC 29575.

Sencore VA62-NT64-VC63 (all three).$500.00. Also, SC60 $400.00, PR57$125.00, LC53 $200.00, DM56 $200.00.Contact Henry Handler, 3018 CornwallAve., Boca Raton, FL 33434.

B&K Model 1420, 1988 last prod. Three-way power, 15MHz original carry caseprobes diagram, dual trace work perfect andcondition. $350.00 negotiable. Sid Karp TV,718-373-8098.

Almost new Sencore VA62A $3,000.00value for $1,500.00. Also, Tentel tensiongauge $400.00 value for $200.00 andTorque gauge 300.00 value for $150.00, orall for $1,700.00. Call 1-503-536-2977.

Vacuum tube voltmeter $35.00, Triplettmulti -tester $7.50, A.W. Sperry multi -tester$7.50 (brand new), 3 -BP multitesters resis-tance check up to 60%2 (brand new)$10.00 each. Joe Oracki, 3502 E. NorthernParkway, Balto MD 21206, 1-410-254-0284.

Tektronix oscilloscope for sale, Model 466w/DM-40 multimeter and Model 454150MHz dual trace. Make offer. Call Mitulat 203-284-2693. Leave message please.

Large stereo -video repair shop going out ofbusiness and selling Sencore & other brandtest equipment. Request list by Fax 601-982-4199 or call at 601-366-0928.

Text books, service manuals, parts,tubes,90%+ off list price. Send two 29¢stamps. M. Seligsohn, 1455 -55th St.,Brooklyn, NY 11219.

Sencore SG80 AM stereo-FM stereo ana-lyzer. Four years old. Excellent condition,rarely used. $2800.00 or b/o. Call Dan at612-253-7392.

Sencore/IBM electronic management soft-ware complete with all revisions and latestupgrade multiuser version. Original cost$3500.00. Will sell for $1500.00/OBO.Call Marge 409-935-3321.

Sencore generator Model VA62A. Almostnew $1600.00 or best offer. 317-852-6779.Dale's TV, 850 N. Green, Brownsburg, IN46112.

Sencore SG80 AM stereo -FM stereo ana-lyzer. Still in box. Call for more info: EddieMatherne, Bayou Electronics, 504-594-3835.

ICOM IC -R70 multi -mode HF communi-cations receiver. Commercial grade,100KHz-30MHz HAM/SWL CW/SSB/AM/RTTY receiver with dual digitalUFO's, direct feed mixer, RF gain, andmore. Very clean/excellent condition. Withdc kit, long wire antenna, and manual-$495.00. Call Dan, 704-252-1928 [email protected].

Sams auto -radio service books from 81 thru171 & Sams Photofacts 1-1079. (Jay's) AnnBichanick, 151/2 W Lake St., Chisholm,MN 55719, 1-218-254-4421.

Tentel, Tentelometer tape tention gauge$275.00. All-Tronix & TV, 402-476-8164.

Sencore VG91 video analyzer and SencoreTVA92 TV video analyzer in original car-tons. Three -months old, $4000.00 OBO.Call 919-790-6808.

Sencore Electronic testing VCR equip-ment, one PR57, one SC61, one VA62, oneCR70, one VC63 and one NIT64. Paid$7385.00 new. Equipment still in orig.boxes. Must sell, best offer! Please call 1-919-793-4521.


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