Question How to diagnose motherboard short? PSU immediately turns off.

[Deleted member 978]

I have an ASUS Z370-P Prime motherboard that will trigger my PSU to immediately power off when I plug the CPU power into the 4 8 pin CPU socket on the motherboard.

I've confirmed it's not a PSU issue, have a PSU testing tool that verified all output voltages are correct and also used a 2nd PSU to double check.

The odd part is that the board will power ON ... IF I only connect the main 24 pin power. I'd like to try and diagnose where the issue resides on the motherboard. I have Oscilloscopes, Digital Power meters, Sin wave generators, and variable power supplies and a electronics microscope.

I've looked at the motherboard under my microscope and I can't see any signs at all of burn marks or failures or issues with trace lines ... has me very puzzled.

Any thoughts of were to begin to try to diagnose this issue?

Cheers, Rob.

 

[CountMike]

I have an ASUS Z370-P Prime motherboard that will trigger my PSU to immediately power off when I plug the CPU power into the 4 8 pin CPU socket on the motherboard.

I've confirmed it's not a PSU issue, have a PSU testing tool that verified all output voltages are correct and also used a 2nd PSU to double check.

The odd part is that the board will power ON ... IF I only connect the main 24 pin power. I'd like to try and diagnose where the issue resides on the motherboard. I have Oscilloscopes, Digital Power meters, Sin wave generators, and variable power supplies and a electronics microscope.

I've looked at the motherboard under my microscope and I can't see any signs at all of burn marks or failures or issues with trace lines ... has me very puzzled.

Any thoughts of were to begin to try to diagnose this issue?

Cheers, Rob.

That bit about CPU power 4/8 pin is sure sign of VRM damage. Take off VRM heat sinks and check VR chips, coils and capacitors. Coils are square chips and VR chips are cowered by heat sink.

 

[Deleted member 978]

Good idea, I'll take a look. I did pull the CPU and no signs of any hot spots nor socket issues.

I have since replaced the motherboard and all good ... but I'm wanting to see if I can actually diagnose and repair this motherboard as a learning session.