Tuesday, September 12, 2017

Finding a short circuit on a Dexter PCB

One of the Dexter PCBs that I was preparing to ship out to customers had a short circuit on it.  After using a multimeter to isolate the approximate area that had the short (by observing voltage drop), I could not find any soldering problems.  So I used a FLIR C2 infrared camera to help me.  After cranking up the current through the VCC power pin to 4 amps to force the short to get hot, here is what the infrared camera was showing (bright yellow is hottest local area):

This is hard to tell what's going on from this blurry image so I've also included a computer generated image with the hot areas high-lighted.

I have now successfully located where the short is by cutting a few traces (I got it wrong the first time, got it right the second time).  Can you do better than I and figure out where the short is without "cutting any traces"?  Hint, the area that is getting hot is supposed to be just VCC (without a connection to ground).  Hint #2, the voltage had dropped substantially on the resistor pad just above the letter 'C' (in CPC1008N) and had dropped to almost 0 on the pad below the 'O' in DIAGNOSE.