Power Supply Turns On Without Pressing Power LED on Motherboard

Oct 1, 2018
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I bought an OCZ PSU (OCZ600MXSP) a little over 6 years ago from Newegg. One day about a year ago I foolishly left my computer on during a storm and lost power. As soon as this happened I made sure to switch everything off and even unplugged the surge protector from the wall outlet.

After the storm had passed I hoped that everything was ok and plugged everything back in. As soon as I flipped the switch on the PSU all the case fans came on and the hard drives whirred to life even though I hadn't pressed the Power LED on the case. This freaked me out a little bit, but after I pressed the Power LED the motherboard booted up and everything seemed to run normally.

I used the computer for the rest of the day with no issues and set the computer to shut down before bed. The shut down process completed and the display went dark, but the case fans didn't turn off. I should mention that the case fans are plugged into motherboard headers, not directly into the PSU.

So now every time I want to turn the computer off I have to shut down, then flip the PSU switch on the back of the computer. Every time I want to turn the computer back on I have to flip the PSU switch, everything comes alive, then I hit the Power LED to boot and continue on my way.

I've been living with this problem for awhile now, and since my build is pretty old it would be the worst thing if I had to start fresh with new components, but I'm wondering if there's something I can do to fix it. Is it the PSU or the motherboard?

Thanks in advance for any help.
 

Ralston18

Titan
Moderator
You mention "hit the Power LED" - is that just an On/Off button/switch with an embedded LED?

Are you able to access the button/switch? Perhaps the switch took a hit is not working as intended.

Take a look. If removable and you know how to do such things, pull the Power LED and test with a multimeter.

You may be able to replace the Power LED with a duplicate or just another unlit push button switch.
 
Oct 1, 2018
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When I said "hit Power LED" I mean the power button the the case connected to the power led header on the motherboard. There is a power button on the motherboard itself (Asrock Z68 Extreme3 Gen3) that works the same as the power button on the case.

I don't have much experience using a multimeter beyond seeing if a battery has any charge left. What would I be looking for exactly with the multimeter?

Update:
My apologies, I think I threw everyone off by calling it the power LED. It's the power switch, not the LED. I've had the LED disconnected ever since I built the computer because the light annoyed me.

I disconnected the power switch connected to the case and just used the power button on the motherboard just now and the same issue remains. Everything (fans connected to motherboard headers, hdds, etc) in the computer turns on as soon as I switch on the PSU, but it doesn't boot up until after I push the power button. The fans and hdds don't turn off when I shut down the system so I have to flip the PSU switch to power down.



 

Ralston18

Titan
Moderator
Continuity.

The button may be stuck (or shorted) in a manner that make it appear as "pressed" to the system. (Hardware)

Or something astray in the system circuitry that makes the motherboard believe that the button is pressed - i.e., some surge or spike related damage.

However, not something to be randomly probed at. Having some previous knowledge and/or circuit schematics is highly recommended.

Do you have any electronically inclined family members or friends?


 
Oct 1, 2018
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If that were the case why wouldn't the system boot up on its own?

So what you're saying is that the PSU is working fine, but there's something screwy with the motherboard. I can't think of anyone I know who has experience messing with motherboard electronics. I'd probably be better off replacing it than paying someone to diagnose it for me anyway.

So I won't plan on replacing the PSU when I upgrade the system in the future.

Thanks for your help.

 

terry4536

Glorious
Herald


Remove the two wires connected to the front panel connectors (power button) on the front bottom corner of the motherboard.

Then try the button on the mother board again. It may also be a problem with the motherboard. If it is and it works otherwise, then decide if it is worth it to you to replace.
 

Ralston18

Titan
Moderator
Only if the PSU switch was on.

For example my desktop has a back switch on the PSU.

To turn the computer on, I flip the PSU switch on and then must press the front button switch to initiate booting.

To turn off, I use "Shutdown" and once the system is off, I switch off the back PSU switch. (Old habit due to "little hands" about that liked to push buttons.)

With neither the case button nor the motherboard button making any difference then I would hazard that the motherboard circuity is shorted in a manner that the motherboard sees as a closed "power on" condition.

I.e., always on and only overall control is via the PSU switch.
 
Oct 1, 2018
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[/quotemsg]

Remove the two wires connected to the front panel connectors (power button) on the front bottom corner of the motherboard.

Then try the button on the mother board again. It may also be a problem with the motherboard. If it is and it works otherwise, then decide if it is worth it to you to replace.[/quotemsg]

I did try unplugging the front panel power button connectors. It didn't fix the issue. Based on what you and Ralston have said I'm thinking the motherboard is halfway stuck on. As I said I've been living with this for about a year now so I guess I'll keep going this way until I replace the whole unit cpu/motherboard/ram in the future.

Thanks for your help.

 
Oct 1, 2018
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Just wanted to post an update. I replaced the OCZ PSU yesterday and everything is working normally now. I can't explain it, but the PSU was the problem not the motherboard.
 

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