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Identify what part is causing a short to GND

cBegue , 09-03-2021, 07:53 AM
Hello there,
I encountered a short circuit during testing on a board due to touching a component with a ground test wire. The board now isn't functional at all.
I see that a particular power line (among 4) after a linear regulator is now shorted (R=1ohm) to ground on the board. I guess a capacitor failed during operation, however I have many between this power line and GND with no apparent visual damage anywhere on the board. (I was looking for a black mark on the PCB)
Would you know of a good way to find the faulty component on the power line if it is possible ?

I would also like to know what you think is a good value for power line (12V/5V/3.3V...) resistance ? Do you think 150-200 ohms is enough ? Or at least 1Kohms ? Can this resistance be too high for example in the Mohm order ?

Thank you for your feedback.
robertferanec , 09-03-2021, 08:32 AM
Sometimes you can find it if the component is getting hot. So, you can touch the components, you can use a thermal camera or you can use some alcohol to find the spot where PCB is hot (alcohol will vapor faster at that place).

Resistance of power lines can vary a lot. For example if there is a termination, you can easily measure resistance of 10OHMs or even lower and that is still ok (e.g. procesor powers, memory interfaces etc).
cBegue , 09-03-2021, 08:49 AM
Thank you for your answer Robert. I've tried with a thermal camera while reducing consumed current with a power resistor, I'll try with higher currents to see if I can find the hot stop.
Lakshmi , 09-05-2021, 06:46 AM
It's could be the capacitor / Diode shorting. You didn't mention which component while testing with ground wire.
As Robert said, a thermal camera is one way.

Have a look at this for reference: https://www.youtube.com/watch?v=VZdOwIuzDXM
If caps are not then try replacing regulator IC.
cBegue , 09-06-2021, 12:03 AM
I found my hotspot: The microcontroller. I guess it is dead then
qdrives , 09-08-2021, 08:12 AM
If the microcontroller is getting hot, make sure that it is not one of the output that has the short.
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