Common Mistakes in Electronics Repair

8/16/2019 Common Mistakes in Electronics Repair

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Common Mistakes In Electronics

RepairMany of us had been interested in electronics repair from a very young age,

but to some, the interest could have started in our 40’s or even 50’s! No

matter what’s your age, electronics repair is fun and this hobby can be turned

into profits if you know what to do with your knowledge t is very e"citing

when you discover that electronics repair is the field that is really meant for

you

#ay and night you search the web for more information about electronicsrepair and hope to be able to understand and solve electronics problems $ou

are %ust simply e"cited and love electronics repair &owever, for a beginner to

become professional level, one needs to avoid some mistakes that beginners

always make 'elow are the ( most common mistakes a beginner should

avoid

1) Not using Isolation transformers


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)n isolation transformer is a linear transformer, often with symmetrical

windings, which is used to decouple two circuits )n isolation transformer lets

an )* signal or power be taken from one device and fed into another device

without electrically connecting the two circuits solation transformers block

transmission of #* signals from one circuit to another, allowing )* signals to

pass solation transformers 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.ard for hot

chassis device such as /M/1 2hat means 340 )* in and 340 )* out $ou

may also use the configuration such as two 340+3 transformers connectedin the below manner

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


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ithout the isolation transformer, e"posed live metal in a device under test is

at a ha.ardous voltage level relative to grounded ob%ects such as an

oscilloscope ground lead 2hat means that if you connect the oscilloscope

ground to the primary side of the switch mode power supply -/M/1, it willcause the building to trip! ith the transformer, as there is no conductive

connection between transformer secondary and earth -ground1,there is no

danger of touching a live part of the circuit while another part of the body is

earthed -grounded1

f you are new in this field, do yourself a favour and get an isolation

transformer 6emember, the power transformer must be rated to handle the

power of any e7uipment connected to it

2) Turning on the equipment and taking measurements

f you are very sure of what you are doing then you can proceed with this kind

of test f you are new and without guidance, you may feel uncomfortable or

have no confidence to turn on the set and perform the voltage or signal test

using either your multimeter or oscilloscope $ou could blow up the power ic

and other components while checking the supply voltage by shorting the **

-#* supply pin1 with the ad%acent pin

had personally heard a %unior tech -many years ago when was working1

shout, 8 want to 7uit this %ob9, simply because he had accidentally blown up a

monitor power section 2hat incident really scared him due to the loud bang

generated by his own carelessness while performing a voltage measurement

when the power was on :ind someone that has this kind of e"perience to


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show you the right way of doing 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 don’t rely 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 electronic components found in a circuit board t had

already been proven that different components need different types of meters

to check them :or electrolytic capacitors, you need an ;/6 meter to test it,

for a


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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 can’t remember every problem that we have solved /imply by referring to

our notes, with a snap of your fingers, you could solve a complicated 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/, don’t %ust write 8no

power in model )+3?4 and the solution is to replace the power ic and an

electrolytic capacitor9 2his kind of note won’t really help you much when you

refer back to it $ou need to write something like 8: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 the problem and the supply voltage to the ic

was still low /o began to check the components related to the supply voltageline and found one electrolytic capacitor -*3C4(uf 50 #*1 had high

;/6 6eplacement of the two components cured the fault9


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Now don’t stop there *ontinue with your notes by drawing a simple power ic

schematic and show where the bad capacitor was connected as shown in the

above photo

$) %oor soldering

f you are weak in your soldering skills, then suggest that you put in more

time to practice it 2his is to avoid a solder bridge that could cause more

harm to the board have seen solder bridges a number of times when

customers told me that the set had been repaired by someone before guess

the repairer could have been %ust starting out, because after removing the

solder bridge and replacing a few components, the set came back to life again


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/imply practice on %unk circuit boards and make yourself good at soldering so

that you will not add more problems to the board you are troubleshooting

&) Improperl installed components

Many times have seen circuit boards that have improperly installed

components 2he technician could actually have solve the problem, but

because of their own negligence, the e7uipment was unable to be

repaired $ou will understand what mean from the photos below


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$ou must be very careful when removing components, making sure they are

put back in the correct location after they had been checked and found to be

good 2here is a possibility a manufacturer could have labelled a component

wrong, however, this rarely happens /o, in order to prevent this kind of


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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 minds like

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 your answer 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 into an online forum, call up your

electronics buddies or course mates, ask your lecturer or your mentor,

etc Many times, asking 7uestions and getting answers will save you hours offrustration

Conclusion D n fact the above article is not only meant for beginners, it is

meant for seasoned repairers too :ind out where your weaknesses are and

learn how to improve them so that your %ourney to becoming a professional

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 having the right mindset and you will

see success very 7uickly

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Common Mistakes in Electronics Repair