How to find a short to ground components

[pronester]

Hi all. This will be my 1st post in this forum.

I am trying to repair a laptop mother motherboard which is an MSI GS70-20C Stealth Edition.

From my diagnose there are few smd caps that are shorted to ground on at least 2 locations (cpu and gpu) on the motherboard.

Currently, I am testing the parts i.e smds, caps and mosfet by taking it out one by one using the hot air to find the short components. As u guys know these process is really tedious and troublesome sometimes.

I want to learn how to find these faulty/shorted components by using the linear power supply to find a short to ground by injecting voltage.

have any of you guys done this method before..appreciate if you can share

 

[Nigel Goodwin]

You can use a low ohm meter - essentially a constant current source which you pass through the board, and measure the voltage drop across the different capacitors - these usually use a 4 wire probe.

 

[crutschow]

The method I've used, when a low-ohm ohmmeter is not available, is to use a power supply to generate a current through the short (say 100mA or more) and then use a voltmeter on its most sensitive scale to follow the voltage drop to the source of the short.
Thus if you measure the voltage drop from one point on trace to another, the drop will tell you the direction to the short current.
If there's no drop across the trace, then the short current is not flowing through that section of the trace.

 

[pronester]

thanks for the reply

The method I've used, when a low-ohm ohmmeter is not available, is to use a power supply to generate a current through the short (say 100mA or more) and then use a voltmeter on its most sensitive scale to follow the voltage drop to the source of the short.
Thus if you measure the voltage drop from one point on trace to another, the drop will tell you the direction to the short current.
If there's no drop across the trace, then the short current is not flowing through that section of the trace.

thanks crutschow for the reply, can u explain how to decide on where to put the +ve wire? the -ve wire is fine that i can put anywhere on the ground source right...

 

[pronester]

You can use a low ohm meter - essentially a constant current source which you pass through the board, and measure the voltage drop across the different capacitors - these usually use a 4 wire probe.

thanks bro, do you have a link for applying this method

 

[crutschow]

can u explain how to decide on where to put the +ve wire?

It can be put anywhere on the +Ve wire where you can make a convenient connection.

 

[Nigel Goodwin]

thanks bro, do you have a link for applying this method

A simple google finds endless links.

**broken link removed**

And one of the members here has some excellent projects:

 

[Mickster]

This doesn't specifically address your query regarding using a PSU to locate shorts, but is a useful method nonetheless, which can be used during your diagnosis.
Shorts create heat, and do so quite rapidly.
Alcohol (IPA - Isopropyl Alcohol) evaporates quite rapidly.
Combine the two and you have a handy, relatively-inexpensive, indication of where a shorted component could be.
Soak a cotton bud/swab/Q-tip with IPA and dab it on the suspect component(s), then apply power.
Instead of removing and testing all of the surrounding components one-by-one, you can now narrow down the suspected short by concentrating upon those components which cause the IPA to evaporate the fastest.

Regards.

 

[BGAmodzX]

this guy's channel is great . He finds shorts on most laptop motherboards. using a combination of psu injection and petrol.

check electronics repair school on youtube .