Need Help, technical problem, Motherboard GA-Z77x-UD3H

[hatem_samir]

I'm facing a problem with motherboard GA-Z77X-UD3H, when power bottom is pressed, the BIOS LEDs light up and fans starts to spin and stops again within a 2 second.

tried to test some components and found the following :
- Short-circuit between GND and 20 MOSFETs Source (red marked).
- PCHIO testing pins, short-circuit between two pins and each pin with GND.
- Two SMD capacitors over the south-bridge chipset, are shorted.
- South-bridge chipset is (+) mark and marked capacitors are shorted also.

please advise your opinion, which component could be reason for this breakdown.

 

[Harald Kapp]

Before you suspect a faulty board: measurements of components in circuit are not very reliable, your suspected shorts may have other reasons and may not be the cause for your issue.

Has the motherborad worked before? If so did you change any bios setups?
Check the power supply's output voltages. I once had an issue with similar symptoms when I activated an energy saving option in the bios. The standby current was too low, the power supply didn't register the motherboard as being on and the power supply turned itself off. I used this trick for a while but then reverted to my prior bios settings.

 

[hatem_samir]

The motherboard was working normally earlier, but this problem used to happen randomly from time to time, computer tuning off (as power failure), removing ram DIMMs and processor and mounting them back, its works again perfectly for couple of week more or less and happening again.

testing the power supply output voltage all was perfect, except -12 volt was reading -11.83 volts.

the onboard voltage testing points supposed to read voltage using Voltmeter when the motherboard is on, but the only PHCIO got a short circuit I don't know is that normal?

also is that normal to read MOSFET source short circuit with GND ?

 

[Harald Kapp]

except -12 volt was reading -11.83 volts.

Not an issue. This is within tolerances.

is that normal to read MOSFET source short circuit with GND ?

Very normal as N-MOSFETs (the gardan variety of MOSFETs) are mostly connected with source to gnd.

works again perfectly for couple of week more or less and happening again.

This could be anything from a bad solder joint, a broken pcb trace, a corroded connector or a stray whisker of conductive material. It is unlikely that it is a component failure.
Visually inspect the solder joints of through hole components, especially connectors, very especially the power connector to the main board for correct solder joints and any loose material.

but the only PHCIO got a short circuit I don't know is that normal?

It is not completely clear to me: do you measure a short circuit or simply no output voltage?
A short circuit is probably not normal, but this may as well be an artefact of your testing method. Unless one knows the circuit connected to this point one cannot say for sure if that is o.k. On the other hand, a short circuit on that net is unlikely to be affected from the procedure you describe swapping components out and back in.

 

[hatem_samir]

It is not completely clear to me: do you measure a short circuit or simply no output voltage?

I cann't test output voltage as motherboard not powering up, I'm just testing the pins using buzzer mode, PCHIO pins reporting short circuit but not the other onboard testing pins.