View Full Version : not sure if mobo or psu dead, opinions? (reps)

04-29-2014, 08:33 AM
alright so my pc wouldn't boot up today, fans spun up fine but the beep was shorter than usual, almost a stutter of a beep and there was no output to the monitor, my initial thought was it was the psu, because it's been there since 2008~, so it should have died by now anyway right?

checked everything was seated correctly on the mobo, noticed "psu fan" wasn't connected so i plugged in the nearest 3 pin connector (upside down??? think i fkn goofed?), when i hit the start button there was a small wisp of smoke and a smell of burning (da fuk?), nothing looked burnt though, no capacitors were burned out, no visible damage, except for a couple of the (copper capacitors?) on top of the cpu's heatsink that already looked damaged when I opened the case, but I figured it was normal for a heatsink?

Haven't checked the underside of the mobo for burn because the wiring in the case is a cluster**** and I cba taking it apart to troubleshoot today.

so i figured out the "pwr_fan" connector on the mobo was upside down, fixed it, fans still spun up but this time no beep? unplugged it again because it doesn't seem to do anything other than I guess fan speed modulation? and turned on the power, fans spun up fine on psu, case, cpu heatsink and gfx card but still have the short beep and no output to monitor.

what should my next step be? I'm guessing it's either the psu (60%) mobo, (20%) or cpu (20%)

other stuff:
the light on the mobo next to the cmos battery is green when I boot up
I've tried swapping the monitor and psu cables, and switching outlets, same result.
have tried the hold start button with no power cable plugged in trick, no good.

specs if needed are something like
atrix 800w psu, since 2008 or so.
ASUS M3A78 mobo, same age as psu
gtx 480 gfx, newest part of system.
6gb ram, 2 new sticks, all working fine for couple of years now.
amd x4 965 relatively new

04-29-2014, 09:22 AM
These are always hard to diagnose. But since there isn't anything noticably wrong with the mobo. and you smelt the burning. I would expect it to be the PSU.

04-29-2014, 09:24 AM
Take off everything not needed to boot and try

04-29-2014, 11:21 AM
Just went through this with a friends new build. Ended up being a DOA power supply.

Anyway, it most likely is the PSU. It might not be giving the motherboard enough power to boot properly, just enough to spin fans. Either you can check with a different PSU (which I'm sure you have thought of) or you can check the 24 pin motherboard connector with a multimeter.

Thinking about it, before doing this, plug the monitor into the onboard video. It seems everything is working but the signal right?

And does the PC stay on after boot? Or does it reset itself