After powering down fans still spin...

[superfuzzy]

My vintage system is built around a Gigabyte GA-k8NS and Sempron Processor.

It runs fine, but after powering down the fans on the power supply (Antec SmartPower 350) and case fans keep spinning. If the power switch on the PSU isn't shut off - the red power light on the front of the case will flicker on and the system will start to beep.

I assume it is one of two things - the PSU or the MB. I don't have a spare PSU - any idea what is causing the problem or how to diagnose it?

Thanks!

 

[Andrius]

You probably have something like "wake on mouse" or "wake on keyboard" enabled and these items have to be powered for that to function. Your mouse probably lights up as well(if it's optical). The motherboard is in a form of deep standby and waits for "wake on xxx" events.

The fact that the fans are on at standby is a bit strange. Have you checked the manual for the motherboard to see if that's an "extra" feature?

 

[superfuzzy]

You probably have something like "wake on mouse" or "wake on keyboard" enabled and these items have to be powered for that to function. Your mouse probably lights up as well(if it's optical). The motherboard is in a form of deep standby and waits for "wake on xxx" events.

The fact that the fans are on at standby is a bit strange. Have you checked the manual for the motherboard to see if that's an "extra" feature?

I didn't make changes to the bios and it's not an XP issue - also happens with LINUX.

I believe that it is either the MB or power supply. I don't have a spare PSU for testing - how can I test to see what the problem is?

 

[Andrius]

The "wake on event" is a motherboard feature. It doesn't care about OS.
Check BIOS (maybe something is on by default).

You could RESET/CLEAR CMOS and/or flash to the newest BIOS.
Also try unplugging the board from the wall over night.

Do the fans stop spinning after say 15 minutes or do they just keep going forever?

 

[superfuzzy]

The "wake on event" is a motherboard feature. It doesn't care about OS.
Check BIOS (maybe something is on by default).

You could RESET/CLEAR CMOS and/or flash to the newest BIOS.
Also try unplugging the board from the wall over night.

Do the fans stop spinning after say 15 minutes or do they just keep going forever?

I checked the bios, and wake on demand is disabled.

When the PC is turned off the fans spin indefinitely, and the power light flickers. It seems like a power leak or something. When the pc is off, I have to also turn off the power switch on the PSU - which is the same thing as unplugging the PSU overnight.

I still think this is a hardware problem - PSU or MB, and need help diagnosing that problem.

Thanks!

 

[Andrius]

Well it might be a hardware problem, but I don't want you to go out and spend money until you are certain what the problem is so I'm trying to work it out.

Are the fans plugged into the motherboard or into the PSU directly?
If they are plugged into the motherboard it would indicate a faulty motherboard.

There's an "easy" way to test a PSU :
http://www.techwarelabs.com/guides/misc_mod/psumod/
Just plug a fan directly into the PSU, start the PSU and then pull out the wire. If the fan keep spinning the PSU is faulty. If it stops it's probably the motherboard.

The being unplugged from the wall over night does strange things to a computer. I've seen this fix problems that were in no way related to your average PSU pointing problem. Like a board refusing to accept FSB settings or windows only seeing one partition on a harddrive.

 

[superfuzzy]

Are the fans plugged into the motherboard or into the PSU directly?
If they are plugged into the motherboard it would indicate a faulty motherboard.

I unplugged the power from the wall overnight and it made no difference.

All fans are plugged directly into the MB. The fans that spin when the PC is turned off are:
1. PSU fan
2. Case fan powered from MB
3. CPU fan

I assume the PSU is OK - but haven't tested it. Could it be anything other than the MB? Could it be the memory? The only card installed is the video adapter.

Thanks again!

 

[Andrius]

I guess not. I don't see how memory could affect the power state. The fact that the PSU fan keeps spinning makes me think the board's power good signal is shorted.

If rechecking and reconnecting the power switch doesn't change anything you'll have to test with a difference PSU/motherboard or RMA the board. It's the likely the board but I would perform the test I linked to above just to be sure.

Good luck.