- The LaST Upgrade -


Last updated March 6, 2023

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

First up, a proper low resistance meter..

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.


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


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...


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...


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

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


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.