gfunkdave

A couple years ago I built my first PC to be a Linux file server. It was working fine until a couple days ago, when I went to ssh into it and couldn’t. I found it was off and wouldn’t turn on.

I had noticed that earlier in the day the lights in the house flickered, and most things that were plugged in restarted. At first I thought it was a bad power supply. I did the paper clip test, shorting pins 16-17, and the power supply fan turned on. I tested pins with a multimeter and got about the correct voltages. I also tried shorting the “Power on” pins on the motherboard to eliminate the switch or wiring as the culprit. So it seems the power supply is fine, and the culprit is a bad motherboard. Does that seem correct?

Visconti

Ah, I'm not familiar with Linux, but assume it's an OS and operates on a similar set of principles as Windows. Do you mean a failure to boot? In other words, when you depress the power switch, the fans fire up, it goes through the boot sequence, and a black screen?

gfunkdave

No, it doesn’t turn on.

Visconti

So, nothing happens when try to power it on?

gfunkdave

Yes, that’s what I’ve been saying.

Visconti

Ok, that's probably a power supply issue. I'm assuming you double checked to ensure all power connectors are still firmly in place? Do you have another power supply to switch and try it? If not, I'd order one from amazon and see if it resolves the issue, before trouble shooting or replacing the mainboard.

gfunkdave

But like I said, the power supply turns on when you short pins 16/17 and shows the correct voltages so it doesn’t seem to be a power supply issue.

Visconti

Understood. Not that I'm an expert but I have been building PCs since I was 16 years old. Over the years, I've encountered twice where a power supply will function in one rig and not the other. In my view, I'd just eliminate the PS first, then go on from there. Goes without saying, select a high quality one with stable voltage at least Gold rated.

gfunkdave

All righty, I happened to have a new power supply I’d ordered when I thought it might be a power supply problem, so I connected it but the computer still doesn’t turn on.

Visconti

Ah, assuming your mainboard standoffs are still in place and all your cables are connected firmly, then you'd have to try another mainboard. During this process, I'd probably just have the mainboard, PS, ram, CPU and GPU (assuming it's not on your cpu), and see if it'll post, before placing it into your case.

StuckInYYZ

So on the assumption all the pins are showing the correct voltage, (Also assuming that if you try to power on the system that the power supply fan doesn't even charge up and power down) Couple of things you could do... most basic, disconnect the power supply and pop out the "CMOS" battery. Wait at least an hour before putting it back in and reconnect the power supply (you could also try the jumper to see if that works) Then I would download the manual for the MB (or if you already have a copy)... it should list all the LEDs on the motherboard and their locations and dispositions. See if they're right or not (while plugged in). After that, inspect all the ICs and capacitors you can see. If it's an IC issue, there might be a hole (divit) in one of the chips... If that's the case, the MB is toast. If it's a capacitor issue (same end result but just to identify the problem) one of the capacitors will be blown (this was an issue when one of the big MB makers got bad capacitors several years back).

Finally, it could also be a CPU issue. Often you can tell by popping the cooling system and then inspecting the underside for any signs of a flaring (but this is a big hassle as you would need to repaste the CPU which is a PITA)

Actually, that's not true. One other simple test you can conduct is to disconnect the storage and try powering it up. If nothing, you can also remove the ram and see if it powers up or beeps (but this is an OLD test)

It's one of those annoying things.

gfunkdave

Well, I'll be. I took out the CMOS battery and the computer powered right up. Before, none of the fans would turn on, the LEDs on the motherboard wouldn't turn on, I didn't hear the hard drives powering up. After taking out the battery (and putting it back) it works again.

Thanks!

StuckInYYZ

This is usualy a discharge fault. I forget the standard, but if the power "outage" is brief enough, it leaves the computer in a dirty state And the only way to fix it is a complete discharge including removing the CMOS battery and letting any associated capacitors drain (they can surprisingly hold onto a charge for quite a while).

Glad it worked out.

gfunkdave

Yeesh, I'm remembering my Embedded Systems and EE classes in undergrad now. It was a very brief outage - just a flicker really. Thanks again!

thomasfly

Glad to hear you were able to resolve the issue with a simple fix like removing and reinserting the CMOS battery, @gfunkdave! I ran into a similar situation last week and I would try this fix in my setup.