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Electronic Repair

Discussion in 'Troubleshooting and Repair' started by Johndon2000, Jun 12, 2013.

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  1. Johndon2000


    Jun 12, 2013
    I am involved in the repair of electronic devices and normally have good diagnostics (i.e. software to test a board and flag up faults in certain areas of the board), but I have some complex boards (200+ IC’s, 200+ resistor networks etc!) that are known to be faulty but other than that there is absolutely no indication where the fault is. Other than the usual clocks/ resets/ voltage levels can anyone suggest how to proceed?! Thanks, John.
  2. davenn

    davenn Moderator

    Sep 5, 2009
    hi johndon
    welcome to the forums

    without knowing a lot more about the boards in question, additional advice would be difficult to impossible to give

    what are the symptoms?
    are these digital circuits ?
    if so TTL or CMOS ?
    or are they analog/digital combos?
    what are the chips types being used ?
    do you have photos of the boards?
    what type of bypass caps are being used of the +V rails?
    have you checked them for failures, particularly if they are tantalums ?

  3. Johndon2000


    Jun 12, 2013
    Hi Dave,

    Thanks for the reply.

    Basically a cct board from a telecomms system. The system just flags it up as Faulty, no other diagnostics given.

    TTL, digital, 40 IC's are SRAM devices, with lots of 74 series glue logic.

    I suspect the SRAMs and could remove them all one by one & test them on a good card but, as they are 44pin devices that would involve desoldering/ resoldering almost 2000 pins & would potentially intorduce another fault (s/c!).

    Many thanks,

  4. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

    Jan 21, 2010
    Johndon, you have so far created three threads for this topic.

    I have deleted two of them.

    If you start a fourth, I will delete it and ban you.

    The simple answer to your problem is that you need to know more about the board. You need to know enough that you can diagnose what is going wrong, then try to fix it.

    The correct person to see may be the same person who designed the board, or the person who wrote the firmware (assuming it has firmware) which detects the failure. Maybe a custom firmware can be written which flashes a code to indicate what the actual fault is.

    Either way, the essential ingredient in fixing a fault is knowledge and we can't help you get that unless you can find a full schematic and a source listing of the firmware and post it here.
  5. Johndon2000


    Jun 12, 2013
    Steve, I didn't realise I had created 3 threads... I kept checking back to see if I had any replies but the threads had dissappeared so I just posted the question again.
  6. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

    Jan 21, 2010
    You can click on "User CP" on the top left of the page and it will take you to a page where you can find all the threads you've started and all the posts you've made.

    Alternately you can use the search function to do the same.
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