common mistakes in electronics repair.doc

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Common Mistakes In ElectronicsRepair

Many of us had been interested in electronics repair from a very youngage, but to some, the interest could have started in our 40s or even50s! No matter whats your age, electronics repair is fun and thishobby can be turned into profits if you know what to do with yourknowledge t is very e"citing when you discover that electronics repairis the field that is really meant for you

#ay and night you search the web for more information aboutelectronics repair and hope to be able to understand and solveelectronics problems $ou are %ust simply e"cited and love electronicsrepair &owever, for a beginner to become professional level, one needsto avoid some mistakes that beginners always make 'elow are the (most common mistakes a beginner should avoid

1) Not using Isolation transformers

)n isolation transformer is a linear transformer, often withsymmetrical windings, which is used to decouple two circuits )n


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isolation transformer lets an )* signal or power be taken from onedevice and fed into another device without electrically connecting thetwo circuits solation transformers block transmission of #* signalsfrom one circuit to another, allowing )* signals to pass solationtransformers also block interference caused by ground loops

n electronics troubleshooting, an isolation transformer has a ratio of+ + which is used as a safety precaution -to eliminate the shock ha.ardfor hot chassis device such as /M /1 2hat means 340 )* in and 340

)* out $ou may also use the configuration such as two 340 +3transformers connected in the below manner

340 +3 -2+1 and +3 back to 340 -231

ithout the isolation transformer, e"posed live metal in a device undertest is at a ha.ardous voltage level relative to grounded ob%ects such asan oscilloscope ground lead 2hat means that if you connect theoscilloscope ground to the primary side of the switch mode powersupply -/M /1, it will cause the building to trip! ith the transformer,as there is no conductive connection between transformer secondaryand earth -ground1, there is no danger of touching a live part ofthe circuit while another part of the body is earthed -grounded1

f you are new in this field, do yourself a favour and get an isolationtransformer 6emember, the power transformer must be rated tohandle the power of any e7uipment connected to it

2) Turning on the equipment and takingmeasurements

f you are very sure of what you are doing then you can proceed withthis kind of test f you are new and without guidance, you may feel

uncomfortable or have no confidence to turn on the set and performthe voltage or signal test using either your multimeter or oscilloscope


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$ou could blow up the power ic and other components while checkingthe supply voltage by shorting the ** -#* supply pin1 with thead%acent pin

had personally heard a %unior tech -many years ago when was working1 shout, 8 want to 7uit this %ob9, simply because he hadaccidentally blown up a monitor power section 2hat incident reallyscared him due to the loud bang generated by his own carelessness

while performing a voltage measurement when the power was on :indsomeone that has this kind of e"perience to show you the right way ofdoing it, otherwise you may create more problems than you want

3) Onl using one multimeter

f you want to be a successful electronics troubleshooter, then dontrely only on one single digital or analogue multimeter 2he more

meters you have, the faster you can detect a fault 2here is no way with %ust one multimeter you can accurately test all the electroniccomponents found in a circuit board t had already been proven thatdifferent components need different types of meters to checkthem :or electrolytic capacitors, you need an ;/6 meter to test it, fora


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!) "ot #riting do#n our solution

henever you have solved a problem, you need to write it down >ur brains %ust cant remember every problem that we have solved /imply by referring to our notes, with a snap of your fingers, you could solve acomplicated problem within minutes or even seconds! &ere is a tip for

you on how to write down those important notes

f you have solved a 8no power9 symptom in a /M /, dont %ust write8no power in model )+3?4 and the solution is to replace the power icand an electrolytic capacitor9 2his kind of note wont really help youmuch when you refer back to it $ou need to write something like 9:rom the @*?A43 power ic datasheet, pin ( should have about +3 to+B #* but found only few volts 6eplacement of the ic did not cure theproblem and the supply voltage to the ic was still low /o began to

check the components related to the supply voltage line and found oneelectrolytic capacitor -*3C4(uf 50 #*1 had high ;/6 6eplacement of the two components cured the fault9
http://www.testingelectroniccomponents.com/wp-content/uploads/2013/05/backlight-tester2.jpg


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Now dont stop there *ontinue with your notes by drawing a simple

power ic schematic and show where the bad capacitor was connected asshown in the above photo

$) %oor soldering

f you are weak in your soldering skills, then suggest that you put inmore time to practice it 2his is to avoid a solder bridge that couldcause more harm to the board have seen solder bridges a number oftimes when customers told me that the set had been repaired bysomeone before guess the repairer could have been %ust starting out,

because after removing the solder bridge and replacing a fewcomponents, the set came back to life again


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/imply practice on %unk circuit boards and make yourself good atsoldering so that you will not add more problems to the board you aretroubleshooting

&) Improperl installed components

Many times have seen circuit boards that have improperly installedcomponents 2he technician could actually have solve the problem, but

because of their own negligence, the e7uipment was unable to berepaired $ou will understand what mean from the photos below


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$ou must be very careful when removing components, making surethey are put back in the correct location after they had been checkedand found to be good 2here is a possibility a manufacturer could havelabelled a component wrong, however, this rarely happens /o, inorder to prevent this kind of mistake, before soldering out any

component, make sure you look at the markings on the board first(1 "ot asking questions

)sking 7uestions is not a sin thus you should not keep them to yourself 'eginners usually have a lot of things playing in their mindslike 8how to check this9, 8how to test that9, 8why did this component

blow9,9 what is the replacement part9, etc $ou should try to find youranswer first before asking the 7uestion as this will force you to think f

you still cannot find the answer, there are several resources where you

can get your 7uestions answered $ou could post your 7uestion intoan online forum, call up your electronics buddies or course mates, ask your lecturer or your mentor, etc Many times, asking 7uestions andgetting answers will save you hours of frustration

Conclusion C n fact the above article is not only meant for beginners,it is meant for seasoned repairers too :ind out where your weaknessesare and learn how to improve them so that your %ourney to becoming aprofessional repairer can be cut short The most important thing is

our mindset ) wrong or bad mindset could cause you to be la.y,have no ob%ective and negative thinking /et your path right by havingthe right mindset and you will see success very 7uickly


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&appy 6epairing

'estine (ong
http://www.testingelectroniccomponents.com/wp-content/uploads/2013/05/jestineyongtestingcomponents.jpg

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