[Abubakar156]

Hi,

I’m troubleshooting a board with a suspected short on one of the power rails. I’ve already checked the resistance to ground and isolated the rail as much as possible, but I’m still trying to narrow down which component is causing the problem.

For this type of fault, what’s your usual diagnostic approach? Do you normally inject a controlled voltage and trace the current path, or is there a better way to isolate the faulty component?

I sometimes use a thermal camera to locate abnormal heating, but on low-current or very small SMD components, the temperature difference isn’t always obvious.

Curious how others approach this kind of fault at the component level.

 

[Martaine2005]

I would briefly check the voltage regulators, diodes, capacitors and output transistors for a short.
Then I would remove the suspect component and check it again out of circuit. Also check the PCB to see if the short has gone. Sometimes a higher current will blow the short open circuit. A thermal imaging camera can be very useful at times. SMD capacitors are quite often shorted to ground.
But it also depends on the item being repaired.
A laptop or an amplifier usually have very different faults. With an amplifier, I nearly always check the output section first.
With a laptop, I’ll check the voltage rails and capacitors.
Having the schematic is also very useful.

 

[danadak]

Also use a low ohm tester that can help with locality on a board.

Circuit: Build a Do-It-Yourself PCB Short Finder

Tired of hunting short-circuits with a magnifying glass? This clever circuit makes locating a PCB short fast, straightforward, and frustration-free.

www.elektormagazine.com

LysVolt MicroOhm - 4-wire precision ohmmeter

I needed a compact and affordable way to measure very low resistances on a test bench — so I built my own USB Micro-Ohmmeter.

hackaday.io

EEVblog Captcha

 

[rainyliveshere]

Why not using a multimeter in short testing mode?

 

[Sunnysky]

Usually it is cracked Caps that fail. But the standard diagnostic is to inject an adjustable lab power supply across the node typically 0.5V to 1V.

Depending on current and power you can then either trace the voltage drop to the short with a DMM or use a thermal camera or your finger to sense heat, if it is more than 1/4W. If more power, it may be visible.