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PCB debug

  1. Sep 15, 2011 #1

    I have a simple populated PCB with passive and active elements. The main chip on PCB is a 8 pin serial EEPROM chip which I am trying to read via PIC microcontroller. Serial chip is tiny and hard to solder wires onto so I can send signals from PIC controller to the chip. I will have easier access via traces onto other elements on the board. I am running continuity test to trace pins to other elements but I get beeps on multimeter that seem to suggest incorrect wiring. I doubt my continuity test technique because it is a commercial PCB. What techniques I can use to ensure I am using the correct pin mappings?

    Thank you
  2. jcsd
  3. Sep 20, 2011 #2
    You can only completely trust a DMM continuity test like this when there are no components installed. Especially with semiconductors (ICs) you can and often do have diodes connected between terminal pins and ground or power (for ESD and OV protections) which can get switched on and appear as a short if you aren't aware of them.

    One work-around is to simply reverse the DMM terminals (which reverses the voltage of the test voltage in continuity mode) and see if you still get continuity. For PCB or solder flaws, the direction doesn't matter but for parasitic diodes in ICs it will.

    Another work-around is often to have the board powered and simply trace out the expected voltage from one side of the path to the other. If it isn't the same all the way along the path, it indicates a PCB or soldering connection problem.
  4. Sep 20, 2011 #3
    Thank you.
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