Stepping through IC chips one by one for troubleshooting

Discussion in 'General Electronics Chat' started by harrison2015, Apr 30, 2015.

  1. harrison2015

    Thread Starter Member

    Apr 22, 2015
    If I turn off the circuit board and I print out the datasheets for every logic chips and analog IC chip and use an external power supply to apply directly to the power pins ( +VCC and ground pin of an IC chip ) to tests its inputs and output. Stepping through troubleshooting each IC chip one at a time with the circuit boards power supply off and nothing else turned on. I'm just stepping through each IC chip one at a time applying voltage to the VCC and ground using an external power supply and then using a logic pulser or function generator to test the inputs and using an oscilloscope to monitor the outputs of the chip. Can this be done?

    The Board is turned off and I'm not using the circuit boards power supply. I'm using an external power supply to apply directly to the IC chip that I want to test, check, verify and troubleshoot. I will tests its inputs using a logic pulser or function generator and monitor the output pins using an oscilloscope. Troubleshooting each IC like this one by one. Can this be done?
  2. dl324

    Distinguished Member

    Mar 30, 2015
    Think about what you're asking. If all of the power pins of the chips are connected together and you apply power to one, what do you think will happen?

    Probably not.
  3. alfacliff

    Well-Known Member

    Dec 13, 2013
    the proper way is to get familiar with what the board is doing. look for where the signal should be, and see if it is there, if not, check the signals going in to the chip to see if they should be there. a lot of times, board failures will be input chips or output chips. look for improper logic levels (floats) these usually indicate a bad chip driving that line.
  4. harrison2015

    Thread Starter Member

    Apr 22, 2015
    True it will. but how else can you step through each IC chip and verify the inputs and outputs?

    To inject the inputs with either a logic pulser or function generator
    To monitor the outputs using an oscilloscope

    When measure the resistance of +VCC to ground, what should a good Logic +VCC to ground resistance be? and other resistance power +VCC rails to ground?

    Some Boards +VCC rail to ground is 1K , 800 ohms , 450 ohms.
  5. harrison2015

    Thread Starter Member

    Apr 22, 2015
    What should be the resistance range from +VCC to ground when there is no problems with a circuit board?
  6. BillB3857

    AAC Fanatic!

    Feb 28, 2009
    That's like asking how much gas will go into a tank. It all depends.....
  7. clementyap

    New Member

    Oct 26, 2015
    Looks like there are no answers to this question.
    Harisson2015, I am in the same situation and untested solution just like yours as there is no way to power up the complex digital circuit board. I do not have access to proper system for the board. The only way is to desolder every IC and test each of them.. It can be tedious.
  8. hp1729

    Well-Known Member

    Nov 23, 2015
    Hold Reset active, if it has one. then put a voltmeter on each pin looking for an improper voltage. Investigate anything that is not a valid high or low. Not flawless, but ...

    Paint the board white with freeze spray, apply power and investigate anything that thaws out unusually fast.