This was my friend's motherboard. He bought a 2nd hand computer which worked for a couple of days after he got it, then died. I troubleshooted it down to the motherboard and he bought a new board, which fixed the problem.
Now I decided to try fixing his old one for fun.
Problem: No POST, No beeps, power button won't shut board down after power up, have to power PSU off at mains.
After having problems with my own machine locking up and failing to POST, which I eventually traced back to leaky power\reset buttons on my case, I started by desoldering the onboard reset button and checking the RESET line (FP_RST#) which turns out to be high (3.3v). So that at least seems OK to some extent.
I noticed that FP_RST# also feeds the "SB700 & RS780 POWER GOOD CIRCUIT" (Page 27)
In this circuit, I measured Q38 to have 5v on its gate, and the output of Q38, the SYS_PWRGD signal is LOW.
This seems to be because Q37 has no base drive, and there's no voltage either side of R209. NB_VCC1P1 rail seems to be down.
I notice that NB_VCC1P1 measures 19.6 Ohm to GND. Is this a short, or normal? The schematic (Page 28) suggests that this rail supplies 10.2 Amps.
Now I decided to try fixing his old one for fun.
Problem: No POST, No beeps, power button won't shut board down after power up, have to power PSU off at mains.
After having problems with my own machine locking up and failing to POST, which I eventually traced back to leaky power\reset buttons on my case, I started by desoldering the onboard reset button and checking the RESET line (FP_RST#) which turns out to be high (3.3v). So that at least seems OK to some extent.
I noticed that FP_RST# also feeds the "SB700 & RS780 POWER GOOD CIRCUIT" (Page 27)
In this circuit, I measured Q38 to have 5v on its gate, and the output of Q38, the SYS_PWRGD signal is LOW.
This seems to be because Q37 has no base drive, and there's no voltage either side of R209. NB_VCC1P1 rail seems to be down.
I notice that NB_VCC1P1 measures 19.6 Ohm to GND. Is this a short, or normal? The schematic (Page 28) suggests that this rail supplies 10.2 Amps.
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