Finding a power rail short with a low ohmic meter

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Finding a power rail short with a low ohmic meter

Post by exxos »

Here is a quick lesson in fault finding a power rail short A low resistance meter.

First up, a proper low resistance meter..

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Basically what we do is check the resistance across various capacitors around the board and look at the resistances.

I started at the bottom right corner of the board working my way up with and to the left taking note of the resistance. Which is 84.2mR.

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Moving upwards on the board you can notice the resistance gets slower, so we are getting closer to the short! Now 35.9mR!


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Now I can only move to the left. So moving along one by one the resistance got lower and lower until there was nowhere else to go...

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This is the lowest resistance point on the whole board on the power rail at 11.3mR.

So checking what capacitor that is on the PCB files...

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..And yes this was a PCB oopies the problem.

I have diagnosed failed ceramic capacitors on motherboards this way as well.

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Overall a low resistance meter is a very useful piece of kit when you have something short circuit on the motherboard. Like on the power rails and have no idea where short actually is.
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