Second opinion on assumed mobo issue

[jamston]

Hey guys

Working on a desktop, its one I built for a family member about 7-8 years ago. I got the call saying it wouldn't switch on, i get there and it's not POSTing, fans are spinning for a split second, power light flashes on then off and then repeats.

So I've took it home, pulled all the hardware from the board and powered it up, fans and light stay on and the board gives one long and two short beeps, this is apparently a video error. As there's no cards or ram or hd in, i was obviously expecting some protests from the mobo. I tried just the video card in next, same one long, two short beeps. I took the video card out and tried each stick of ram in each slot and tried booting, each time it does the fan spin, power light flash and no POST. So now i'm thinking bad ram, so i put the ram in another desktop and it posts fine, it also does two passes after an hour or so on memtest, not the ram then. Installed the video card in the other desktop, that installed fine too.

So everything points to the mobo, the psu seems ok because i can get it to stay on and do some kind of post beeps, so that seems ok. The only thing left is the mobo. I dont have a machine I can test the cpu in, but I'm guessing/hoping thats ok and its only the mobo, what do people think?

 

[NYJimbo]

The quickest thing is to check the voltage on the CMOS battery. If that's ok make sure you check the mobo for bad caps. It would really be great if you could put in a alternative PSU or at least test that.

Too much guessing going on without the right testing.

 

[jamston]

Tested the CMOS battery with a multimeter, 3.1 volts. No obviously bulging or misshapen caps on the board. I do have another psu, but its in a machine, so its possible but a pain to do. I'm still waiting on a PSU tester i ordered nearly two months ago off ebay.

 

[CNS]

you are getting a POST so you can pretty much rule out any CPU issue. After looking for bad caps and removing all hardware i would also agree to test another PSU. If results are the same then i would deem a MB issue.

 

[mr m]

When I have flashing lights and no POST I also look at the USB ports with a magnifying lens.

2 Months and no tester? I"d write that off by now! I use an old mobo and a hdd to load a PS that I want to test. As nyjimbo said, install a spare PS to be sure. I've had all voltages test within spec yet the PS was still bad.

 

[JustInspired]

Definitely try another power supply and check for case/motherboard grounding issues. Also bear in mind that power supply testers are not always correct. If they say the PSU is bad then it's almost certainly bad but if it says it's good then it MAY be good. This is from experience with a few different ones. Sometimes a supposedly good PSU won't work right under load.
Oh and don't make the mistake of leaving the PSU tester connected and on for any length of time. I left one running to see if there would be any issues when it warmed up and that was an almost catastrophic mistake. I came back to a melted burning mess that used to be my tester. Just in time I think!

 

[jamston]

Tested with the other PSU, same behaviour exactly, motherboard it is. I see an ebay purchase ahead. Thanks for the input guys.

 

[jamston]

Checked the USB ports and all look fine, nothing bent or misshapen and likely to cause a short. The board was filthy though, i had to pull the fan and heatsink apart and clean the smokers home dust from it.

 

[Encrypted Existence]

Swap the PSU out for a known good. Also, test the RAM more thoroughly. I believe PCX preaches at least 6 passes with memtest 86+ and try taking the CMOS battery out and try to boot (I know, a long shot, but just to be sure). Have you checked for swolen caps?

 

[FremontPC]

Looks like he already checked for bad caps.

Just for the halibut, pull the power cord and hold the power button down for 20 seconds or so, then hook the power back up and give it another shot.

What mobo is it?

 

[jamston]

When your suggesting booting with the battery out and doing an ATX reset, do you suggest any hardware is left in?

The mobo is an Asus P5B

 

[FremontPC]

I'd leave the video card in, any others should come out. I don't think you need to pull the battery for this, just the power cord.

 

[jamston]

Yeah just the same, slight spin flashing power. Ah well

 

[FremontPC]

Thanks for giving it a shot!