How to determine if an smd board has shorted component

[jerryk]

I am working on an smd board that had an alkaline batter spill on it.  So far I have found two shorted components on the board and removed them.  Additionally there were three IC's (logic gates, 555 timers) that were heavily corroded so these were removed and the pads cleaned with vinegar and then alcohol. While testing all the capacitors on the board I have found two that while in circuit showed continuity.  I have removed them and they test fine with a capacitance of 100nf and no continuity.  However, both mounting pads for each capacitor show continuity with ground and zero resistance across the pads.  Does this indicate that there is a shorted component on the board that I have yet to find or is this really a legitimate circuit where both poles of a capacitor are attached to ground?

Jerry

[klr5205]

Your instincts are correct that both leads of a capacitor would never go to the same net by design because in that case the capacitor isn't even in the circuit!

Since the short is still present after removing what were likely decoupling caps, chances are that your power supply is shorted for some reason.  Check the supply itself and any chips that it powers.  One of them probably failed and shorted its power rails internally.

[jerryk]

The large electrolytic on the left was shorted so I have replaced it.  There also was a shorted shottky diode at D5 on the left that had shorted and it's replacement has yet to be installed.  The capacitor locations in question are C54 and C85 on the left and their traces on one side are difficult to follow since they connect to the center layer under the ground plane on the surface.  I'm tempted to do the heat test by running some small voltage and current at both capacitors poles but I don't want to burn a trace that connects to an internal layer.  I have checked all other caps and resistors/networks on the board and they seem to test ok. I'm open to suggestions.

Thanks - Jerry

[vk6zgo]

Your instincts are correct that both leads of a capacitor would never go to the same net by design because in that case the capacitor isn't even in the circuit!

Not always-------think parallel LC tuned circuit, where the inductor would often look like a short circuit to a dc test.

Your DMM is a dc/low frequency device, & doesn't always recognise the circuit that is there.