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How to find a short to ground components

pronester

New Member
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

Super Moderator
Most Helpful Member
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

Well-Known Member
Most Helpful Member
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

New Member
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...
 

crutschow

Well-Known Member
Most Helpful Member
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.
 

Mickster

Well-Known Member
Most Helpful Member
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

Member
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 .
 

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