6am
2 Bronze

Optiplex 9020 SFF PSU or motherboard power issue?

Hi, hope someone can shed some light on this problem:
Recently my 9020 SFF has started acting up, originally with the fans randomly turning on when the pc was powered down, and now with the fans constantly running even when the pc is shutdown fully.
Here's as far as I've been able to diagnose the issue:

1. The BIST (built in self test button) is *constantly* lit up green without me needing to press the test button.
It should only light up when the button is pressed, so maybe PSU faulty?

2. Disconnected PSU from motherboard and connected to power.
RESULT: BIST light is off. Turns green only when BIST button is pressed. Maybe PSU *not* faulty after all?

3. Plugged PSU into motherboard using ONLY the 4 pin power connector.
BIST lights up green when tested. Otherwise light is off. That's good I guess. Narrows things down a little..

4. Plugged PSU into motherboard with ONLY the 8 pin power connector.
BIST light is on green AL THE TIME, no need to push test button. That narrows it down to the 8 pin power connector, I guess?

5. Disconnect everything from motherboard except PSU. Reconnect things one by one to see if one thing is triggering the constant green BIST light. No change. Green BIST light on constantly whether anything is plugged into board or not. So, maybe the motherboard *itself* is triggering the constant BIST green light?

At this point, all I can figure out is that either the 8 pin cable part of the PSU is faulty, or the motherboard is faulty and triggering the PSU to supply a tiny trickle of power which keeps the fans running constantly?

I've played with every BIOS setting I can think of the make sure it's not in some weird low power state, but with no success.

Does anyone here have any further ideas or have you seen this same issue?
I want to avoid buying a PSU only to find its a motherboard issue, or vice-versa, or having to buy both as it's probably cheaper to just replace the whole pc.

Thanks for any help and sorry for the long post!
v

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3 Replies
bj11213
3 Argentum

Re: Optiplex 9020 SFF PSU or motherboard power issue?

The fans are controlled through the motherboard (and btw it takes more than "a tiny trickle of power" to run them)

 

Does the system appear to run normally apart from having the fans running when the system is "shut down"? If so I doubt very much whether it's a power supply issue. Perhaps you can live with the problem by uplugging the system from the wall socket when it's not in use. (Shut it down normally first otherwise the disc will get corrupted!)

 

My suspicion is that a temperature sensor or its connection to the motherboard has failed.

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6am
2 Bronze

Re: Optiplex 9020 SFF PSU or motherboard power issue?

Hi bj11213,
Yes, the system runs fine when powered up. Windows 10 runs fine, both fans work as they should, all devices appear to function ok. It's just when system is shutdown the fans continue to run until I pull the plug from the case.

I've considered living with the prob temporarily as I can still access everything, but obviously making sure my backups are up to date. The thing that concerns me is that it progressed from "the fans suddenly turning on randomly when the computer was off" around one week ago to "the bloody fans won't turn off at all" today. Who knows what will happen next week. Plus it's the wife's computer, so she definitely won't love the idea of constantly plugging/unplugging to use it

Spoke to Dell support, it's old and out of warranty so no longer their issue, but they say some test suggest it's the motherboard as you say.

Also might look into buying another exact optiplex 9020 and swapping in the harddrive to pickup up where I left off.

Thanks for your insight!

v

 

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bra51776
3 Argentum

Re: Optiplex 9020 SFF PSU or motherboard power issue?

This is all fantastic isolation troubleshooting.  Did you run any diagnostics to see whether there was a Mobo or a PSU code thrown on ePSA check or via Dell Support Assist?

 

Boot up, mash F12 until the one-time boot menu pops up, scroll down to diagnostics, and run ePSA if you haven't already.  It might point to Mobo or PSU directly.  If the short check works, I'd run the full long check too.

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