Fan causing PC to not boot?

[xxsilk109xx]

I had a customer last week bring me a dell dimension 4700. It would turn on but the cpu fan, which is attached to the back of the case would just spin real fast and real loud and there would be nothing on the screen.

I unplugged the fan, started the computer, booted great, except for the error about the CPU fan not being attached, i then plugged the fan in and it ran normal. It had lots of windows errors and virus problems, old accts etc. So he wanted me to wipe it clean. I did with no issues. Tested the ram and HD before I did it as normal. Got it up and running great with no issues.

He takes it home and it has been working great, so he says. He calls me today and told me that this morning he went to turn it on and the fan was doing the exact same thing.

I figured that it was just a loose connection the first time, but now I am starting to wonder why it happened again.

anyone experience this before and care to offer any advice?

[14049752]

It's very unlikely that it's the fan. More likely early signs of mobo failure somewhere. I think the 4700 was one of the ones with all the bad capacitors.

[xxsilk109xx]

I checked the caps and there were no busted or raised ones... i hope its not the mobo failing..

[Martyn]

If the fan is running too fast maybe there is a problem with it and it is drawing too much current. So after it boots you can reconnect the fan and it runs at the right speed? or not? Test the voltage being supplied against what it should be.

[xxsilk109xx]

yes after i unconnect it and boot it, i then plug the fan in and its run normally, speeds up when getting hot, speeds down when cooling down..

[Martyn]

Well it sounds like its overloading or the psu has a problem. Have you tried another psu or another fan?

[xxsilk109xx]

i didnt try another fan or power supply, i will try that next. However, the fan i will have to order because of the connection on the motherboard is not the standard type, its proprietary dell.
i put it on the PSU tester and it seemed fine, of course that was not under load.

[AdamsAPlus]

I would change out the fan first. To me it doesn't make since that a fan would be pulling too much power but from what ever thing else you have said I feel it has to be the fan. I would swap it out with a known good one.

Does he have any fan controllers? If so check the settings. Or if he has a temp gage make sure the probe is in the correct place.

You said the cpu fan, which is attached to the back of the case I'm a little confused by this statement. Is it the CPU fan or the Case Fan. I know some of those dells have a cpu fan with a green plastic thing attaching the air flow it to the back of the case. Is that what your talking about?

[Martyn]

It's best to have a couple of power supplies around for testing. As you know the tester doesn't tell you if the psu is causing problems only that the voltages aren't there that's why you need a spare or two.

[xxsilk109xx]

yes im talking about the fan that has the green shroud in place...