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Comparing Identical Circuits For Troubleshooting

By on May 14, 2011

lcd monitor board

If you are repairing  equipment that have two (like LCD Monitors) or more similar circuit  (like TV R,G,B) then you can compare the circuit and find the solution fast. Many times when troubleshooting the LCD Monitors (especially the one that is new in the market or the model that you have not repair before) that have problem in the inverter board (display shutdown after few seconds), i always compare the top and the bottom circuit. I will use analogue ohmmeter to compare both the circuit. By right similar circuit will have similar ohm readings and if there is any differences in the resistance reading then you know that something have gone wrong. It will be the clue for you to troubleshoot on that particular area.  You can compare the transistors, high voltage transformer or any components in the circuit. In certain circuits you may have to discharge the cap voltage as it could affect the meter’s reading.

If you have the scope you can also use it to compare the signals between the circuit. For example, comparing the waveform of the Red and the Blue circuit in TV/Monitors. It should have slightly similar waveform and if you got any out of shape waveform then you know there is a problem in that circuit. If you have the Huntron tracker that will be even easier because Huntron was designed to serve this kind of purpose.

The best way to improve your skill in comparing the circuit is to understand how the circuit works first with the help of some schematic diagrams. Try get a good equipment and start to compare the circuits. Write down all the important info you have measured for future reference. With this way you will ever ready to compare any circuits that comes in to your repair bench.



  1. Kasim

    May 15, 2011 at 1:56 am

    Thanks for sharing your knowledge with us.
    I want to understand working of a crt and lcd tv ckt diagram . I know it is dificult to understand each and every model. So i need to focus on one specific model. Can you please sugest me one good model no of crt and lcd monitor(the ckt diagram or mannual should be freely available

  2. admin

    May 16, 2011 at 4:39 am

    HI Kasim,

    Actually either crt or lcd monitor diagram they are more or less the same. Download few of the diagrams and begin to compare the circuit. Yo can try


  3. neyod

    May 17, 2011 at 10:35 pm

    thanks for this info.this is one of the best and easiest method a technician can use to troubleshoot a system especially those that are proving difficult.i'd tried it a lot and it really works ,its just that great caution must be excercised so one will get the working circuit damage in the course of comparing with another.

  4. admin

    May 17, 2011 at 11:13 pm

    HI Neyod,

    You are right, one has to be careful when comparing with a good board otherwise the good one may give problem by our mistake.


  5. Amir Mukhtar

    May 26, 2011 at 5:11 am

    Sir Jestine
    Thanks you again to share a valuable information regarding repair ideas in order to fix faults not only fast but it also satisfactorily.

    i appreciate you and your services as humanitarian in this regards...

    thanks you
    yours student
    Amir Mukhtar


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