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Oct 25th, 2007
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Dead but Power on without Switch

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Hello,

I'm the IT guy for our factory and I'm trying to determine what has killed several PCs.

Here's the scenario - a computer runs fine but one day it either refuses to power on by the button or, we're using it and it suddenly shuts off, then refusing to come on by the button.

If the unit is unplugged and then plugged back in it suddenly comes on but never posts. Swapping power supplies has no effect. The moment the PSU is plugged in (and if it has a switch on it, the switch is on) the system fans start and all the case lights come on (both power and HD LEDs even though no IDE cables are connected).

I've pulled the wires from the front panel header in case the front power switch was stuck on. No effect. I've got a bare motherboard with only the power plugs attached, a cpu, cpu fan, and memory and NO OTHER WIRES OR ADAPTERS. The second the power is plugged in the fan comes on. If the power supply 20 pin connector is not connected the power supply stays off.

I've seen this happen about four times to different systems scattered throughout the factory and plugged into surge protectors. Twice it has been an E-Machine with an AMD socket 754 and a power supply that had no on/off toggle build directly into the PSU.

This time it happened to a brand new MSI K8MM3 motherboard. It posted fine yesterday. Today I set the BIOS to use 'Cool and Quiet' and "Smart Fan" and when I went to view the motherboard hardware status screen the screen went black and the system died. Once I pulled the plug and plugged it back in, the "living dead syndrome" started. Fans all on but no post.

Is this a common problem for other people? Has anyone ever found the source of the problem?

Thanks,
Ric
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regkaz is offline Offline
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Oct 25th, 2007
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Re: Dead but Power on without Switch

Very difficult at a distance to diagnose. But it seems there is a common cause; unlikely to be the PC, so it's possibly the mains. Ant-surge devices need really good chokes to work and there's probably a capacitor gone behind a sensing switch that blows with the surge. Or even worse.

Factory, power surges? Yes? Lots of 3 phase stuff; on/off, in/out shake it all about?

that's my shot from a distance.
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Oct 26th, 2007
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Re: Dead but Power on without Switch

There are two common factors to all my dead PCs. They were all plugged into the factory electrical system and they all had the cheap PSU you get with a budget PC.

I've taken a meter to these PSUs after a mobo fail and they all read just within acceptable tolerance without any load. If it's electrical spikes killing my PCs it is just enough to to take out the mobo without significantly harming the PSUs.

As to our factory power I must agree with your diagnosis. I know our main server is constantly sending the admin account warnings about the UPS being activated (whether for spikes or drops I'm not sure). We have several 3 phase machines and some rather suspect wiring throughout the plant. Despite surge protectors and battery UPSs on most of the units I wouldn't be surprised that it's a power issue.

I guess I was hoping to hear that certain cheaper PCs or a particular brand of mobo was notorious for this problem but surges make more sense. As an added note I pulled everything off the last mobo, including the CPU, CPU fan, and memory. It still turned on the power supply the second it was plugged in.

My solution will be verifying that everything is surge protected and replacing the PSU along with the motherboard on all future fails.
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Re: Dead but Power on without Switch

Pleased to have been of assistance.

I've got an industrial strength UPS attached to my two PCs and that's at my home office. I hear it clicking in all the time (well not all the time but you know what I mean). The choke on that thing deals with it.

So the longer term solution for your factory should include well choked UPS devices either at the distribution level (expensive because of the install work and capacitiy you'd need), or at the deskside level - not inexpensive but cheaper than regularly scrapping your PCs.

Incidentally no PC can withstand surges and the "best" of them included. What's lightning proof sort of thing?
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