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branchingfactor
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PC Won't Start - Replaced P/S - What's next?

Fri Nov 15, 2019 6:54 pm

Help! My PC turned itself off while I was using it and won't turn back on. I replaced both the powersupply, coin cell battery, and the power button but it still won't turn on. The Intel DP55KG motherboard has a green light indicating it is receiving 5v power but even the motherboard power-on button won't turn it on. It's 10 years old. The new powersupply (Corsair RM750x) makes a small noise when I push the power button but none of the fans on the power supply, cpu, gpu, or case spin up and I don't see any other signs of activity.

What's my next debugging step? Thank you!
 
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Re: PC Won't Start - Replaced P/S - What's next?

Fri Nov 15, 2019 7:09 pm

If it’s 10 years old, maybe it’s time for a new(er) system.
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Re: PC Won't Start - Replaced P/S - What's next?

Fri Nov 15, 2019 7:26 pm

You're going to spend WAY more in debugging than you will for a new box.
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Re: PC Won't Start - Replaced P/S - What's next?

Fri Nov 15, 2019 7:34 pm

branchingfactor wrote:
The new powersupply (Corsair RM750x) makes a small noise when I push the power button but none of the fans on the power supply, cpu, gpu, or case spin up and I don't see any other signs of activity.

Sounds like something may be shorted out, causing the power supply's overload protection to kick in. Look around the CPU area, and check for bulging capacitors or scorch marks. You may have suffered a catastrophic VRM failure.

Also possible some other component has shorted out. Try disconnecting power from all of your storage devices and unplugging all USB peripherals, and see if you can get the motherboard to power up.
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branchingfactor
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Re: PC Won't Start - Replaced P/S - What's next?

Mon Nov 18, 2019 7:26 am

I disconnected all peripheral power and USB power but no change. The only connections from the power supply are to the motherboard and cpu.

Do I also need to disconnect the SATA connectors?

Do I need to provide power to the graphics card for the motherboard to boot?
 
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Re: PC Won't Start - Replaced P/S - What's next?

Mon Nov 18, 2019 7:47 am

Try the (maybe) easy stuff first... remove and reseat memory, remove the CPU and reseat it. Otherwise, as noted in other posts, a VRM or other key component may have died.
 
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Re: PC Won't Start - Replaced P/S - What's next?

Mon Nov 18, 2019 7:47 am

branchingfactor wrote:
I disconnected all peripheral power and USB power but no change. The only connections from the power supply are to the motherboard and cpu.

Do I also need to disconnect the SATA connectors?

Should not be necessary if you disconnected the SATA power leads, and is unlikely to help, but couldn't hurt.

branchingfactor wrote:
Do I need to provide power to the graphics card for the motherboard to boot?

Unless you've got integrated graphics you probably need a GPU to POST. But you should at least be able to get the CPU fan to spin up.

It is possible that the GPU could be shorting something out even with its power lead pulled, since it can also draw power from the PCIe slot. I would actually recommend pulling the GPU and switching to IGP (if you have one), or installing a spare older GPU to rule out the possibility that the culprit is the GPU.
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Re: PC Won't Start - Replaced P/S - What's next?

Mon Nov 18, 2019 8:00 am

You said the PS made a small noise but that its fan didn't spin.

One troubleshooting step would be to disconnect the PS from everything, remove it from the case, and see if its fan will spin when you plug it in and flip it's power button. If it doesn't, that's probably your culprit.
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Re: PC Won't Start - Replaced P/S - What's next?

Mon Nov 18, 2019 10:14 am

K-L-Waster wrote:
You said the PS made a small noise but that its fan didn't spin.

One troubleshooting step would be to disconnect the PS from everything, remove it from the case, and see if its fan will spin when you plug it in and flip it's power button. If it doesn't, that's probably your culprit.

You'll need to hotwire PS-ON pin (short pin 16 to ground) of the PSU to get it to power up standalone like that. A paperclip will do in a pinch.

There are also some PSUs that won't power up without some sort of load connected, so the test isn't 100% conclusive.

OP also indicated that he already replaced the PSU, so that's unlikely to be the root cause unless he received a defective replacement PSU.
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branchingfactor
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Re: PC Won't Start - Replaced P/S - What's next?

Mon Nov 18, 2019 11:43 am

just brew it! wrote:
K-L-Waster wrote:
You said the PS made a small noise but that its fan didn't spin.

One troubleshooting step would be to disconnect the PS from everything, remove it from the case, and see if its fan will spin when you plug it in and flip it's power button. If it doesn't, that's probably your culprit.

You'll need to hotwire PS-ON pin (short pin 16 to ground) of the PSU to get it to power up standalone like that. A paperclip will do in a pinch.

There are also some PSUs that won't power up without some sort of load connected, so the test isn't 100% conclusive.

OP also indicated that he already replaced the PSU, so that's unlikely to be the root cause unless he received a defective replacement PSU.


Yes, I tried hotwiring the PS-on pins but the fan didn't spin up on either the original powersupply (Corsair hx750) or the two replacement power supplies (Corsair rm750x. I think the fan only spins under load for those power supplies. One strange thing is that the 12v pin only gave 5v and every other pin has 0v.
 
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Re: PC Won't Start - Replaced P/S - What's next?

Mon Nov 18, 2019 3:23 pm

You can pick up a cheap PSU Tester (~$15) and see if the old PSU was bad. Typically these cheap ttesters use a resistor and can only stand PS power for a couple minutes but take the opportunity to check the various voltages. If the old PSU is bad or any voltage is bad, there is a slight chance that it took out your memory and/or CPU when it went down. It depends on whether it died in a surge or brownout (thus more likely damage downstream) or if it just died of a bad component (expired quietly possibly no damage downstream).

Also, inspect the caps on your motherboard. Do any of them bulge or have crud beneath them? If so, that can prevent booting and might take down a PSU. If its bad caps; the CPU and memory might be OK. It depends. Caps can be replaced, but it needs an experienced hand and you never know what might be burned as a result of the caps going.
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