Need help troubleshooting a new pcb

Discussion in 'General Electronics Chat' started by vandaycalta, Jun 8, 2016.

  1. vandaycalta

    Thread Starter Member

    Mar 22, 2016
    I had some pcb's made by advanced circuits using the latest version of Eagle. I had mocked up and proven out on a breadboard my circuit of which I will not post here, So I know my circuit is functional. After I built the circuit on the pcb and powered it up I noticed that the 5v reg was hot and disconnected power and probed my circuit with my meter as well as visual under a scope for shorts but I can not find any. I have bad continuity across my .1uf caps for decoupling and have removed 2 of 4 of them starting from closest to the v reg. I probe the pads on the cap I just removed and still have bad continuity. I think I have a short to ground but can not find it and dont know what else to do. A fresh board with no components meters fine. All of my parts have been derated. This is a double sided board. Any suggestions on troubleshooting would be appreciated.

  2. dl324

    Distinguished Member

    Mar 30, 2015
    Define is bad continuity. Power the board and measure regulator voltages.

    Does board function?
  3. paulktreg

    Distinguished Member

    Jun 2, 2008
    Don't always presume a circuit that works on a breadboard will work on a printed circuit board especially so when moderate to high frequencies are involved.

    Breadboard > Prototype PCB > Final PCB is the way to go?

    You'll need to post your schematic and PCB layout if you're going to get any help.
  4. mcgyvr

    AAC Fanatic!

    Oct 15, 2009
    Did you pay for electrical test on the PCB? That will rule out any net to net shorts..
    But as you stated the "short" isn't present on a new unpopulated board so that rules the board out..
    So we are done here until you can provide more detailed information..

    Its NEVER easy to diagnose problems with someone elses circuit without any real information over the internet..
  5. ronv

    AAC Fanatic!

    Nov 12, 2008
    I'm going to guess bad continuity is a short??
    If the empty board is not shorted I would visually inspect the 5 volt line for any bridges that might go to ground.
    If that doesn't work you could start to populate your spare board with parts starting with the regulator and measuring as you add sections. This may be difficult depending on your boards circuits.
  6. Dr.killjoy

    Well-Known Member

    Apr 28, 2013
    Is the Vreg heatsink tied to ground or the caps could be bad ???
    Roderick Young likes this.
  7. Roderick Young


    Feb 22, 2015
    Using one of the bare boards as a guide, I'd follow the 5 volt power net and look for shorts to ground, or bad soldering. If I couldn't find anything on the loaded board, I'd start removing components powered by 5V one at a time.
  8. KeepItSimpleStupid

    Well-Known Member

    Mar 4, 2014
    Devices like these work. I bought something many years ago called ShortSqueek.
    But essentially a tone milliohmeter.

    Without full electrical testing, you have no idea if it's the board or a component.
  9. hp1729

    Well-Known Member

    Nov 23, 2015
    Can you bring the board up a small circuit at a time? Populate only the power section and see if that comes up, then add other circuits one at a time.
  10. ErnieM

    AAC Fanatic!

    Apr 24, 2011
    Try the smoke test: power the board up, and the component that is bad will emit smoke, or at least get warm which you can detect with your finger.

    Finding shorts with an ohmmeter is difficult as there is very little difference in resistance across the power lines, but a very accurate 4 point probe meter may work. Or... make do with any source of current and use your voltmeter (usually more accurate than a common ohmmeter) and find the lowest voltage hence the lowest resistance hence the shortest short and the problem.