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Case Fans/Hard Drive LED light on after shutdown

By ncrhodes ·
I am having a weird problem with my computer when shutting off through the normal XP shutdown process.
The hard drive LED light at the front of case stays on, the case fans (connected to PS connectors, not MB)and my Video Card fan all spin slowly. I checked the voltages on the +5v and +12v rail, and both read 3.75 v when the computer was off.
The PS is new, MB is 2-1/2 yrs. old. I checked on Google and found a search on this site that had someone with a similar problem and the MB was found to be bad...I think someone mentioned a leakage path between the 5 volt standby power, and the 5 volt main power as maybe the problem.
The computer works fine otherwise.
Any other thoughts would be appreciated.

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Sounds like the power supply

by TheChas In reply to Case Fans/Hard Drive LED ...

The fact that you have voltage on the +12 line points to the power supply itself as the source of the problem.

I would start by trying a different power supply. That way, you rule out the much easier to change power supply first.

A related thought is that you may have too large of a power supply. While it is better to have too large a supply than too small of a supply. With switching power supplies, it is possible to have too big of a power supply for the system.

Switching power supplies need a minimum load to operate properly. Some designs also need a sufficient load to allow them to shut down.

One test would be to see what happens when you shut off AC power to the supply and then turn it back on. If the lights and fans stay off when you enable AC power to the system, but stay on when you shut down the PC. Then, the PC does not load the power supply enough for it to shut down.

Chas

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Possibly Faulty Power Supply

by ebouza In reply to Case Fans/Hard Drive LED ...

Do the lights and the fans shut down eventually? If they don't it sounds like it is a defective power supply. What happens if you unplug the power supply from the wall?

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Still not sure if its PS

by ncrhodes In reply to Possibly Faulty Power Sup ...

Thanks for the response.
The PS is brand new: Thermaltake Purepower 430W
Mobo: ASUS A7N8X-E

A little more history here might be needed.
The PS is new (2 weeks) after my old one fried. The computer was in stand-by mode, when all the sudden it shut-off and the PS smoked. Don't know if this was caused by a bad PS or MB. And this may or may not be relevant to my problem, although I am hesitant about putting the computer in Stand-by mode again if it's MB related.

New Power Supply:
The case fans connected to the MB do shut down. The case fans connected via the PS 4 pin connectors stay on as does the video card fan and hard drive LED light at the front of the case. When the PS is unplugged from the wall, everything does shut down.

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This is a USB problem

by csmith In reply to Case Fans/Hard Drive LED ...

This problem is caused by 5 Volts feeding back from an external USB device/powersupply.
The reason the 5 Volts feeds back is that manufacturers (As remember, Sharktoon is an example) cut costs by eliminating the necessary diode to prevent this problem.
The fans turn slowly because they are receiving 5 Volts instead of 12 Volts.

There is nothing wrong with your power supply. The computer works normally when powered up because the computer power supply applies 5 Volts to the USB, cancelling the effect of the external USB device, and there is thus no current flow in the USB cable.

Regards, Chris

P.S. LEDs only require about 2 Volts to function.

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Problem Solved......USB Device

by ncrhodes In reply to This is a USB problem

Chris,
Thanks for the help. You are right. I have a Maxtor One Touch USB External Drive that has 2 USB connections, the 2nd being to power the hard drive.
Even though I didn't have the drive connected, I unplugged the 2nd connector, shut the computer down and sure enough that solved the problem. I would have never guessed that was the problem.
Thanks again for the help.

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have same problem

by gdemarest In reply to This is a USB problem

tried everything they told you didn't work for me. I'm starting to think it is my power supply. Change mother board. cpu, and memory. problem still the same. only thing left is the power supply.

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