Interesting PC problem... I'm guessing PSU?

Zangmonkey

Zangmonkey

Supreme [H]ardness
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Jul 6, 2005
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A friend's computer starting acting up. The fans spin up, lights go on but display shows "No signal".


I brought it home and plugged it into my bench and everything worked fine. I suggesting their display may be a problem. So I dug out a spare display, tested it (worked fine here), then brought it over and hooked everything back up.

Same thing happens... fans, lights, "no signal".
Nothing is plugged into the machine except for the monitor so there is no peripheral failure.


I have some more testing to do but I am thinking of what could cause this.
The only difference between there and here is that on my bench it's plugged into a UPS and there it's plugged into a wall (I also tried different sockets).

Could it be that their power is too dirty or too low or too high at their house? PSU is the best I have to go on right now but I'm looking for input.
In a little while I will listen for post beeps.
 
My guess is MB, because the fans shouldn't go on if PSU is dead.

Any chance of plugging the PSU in question into a working system (nothing expensive k?) and testing it?
 
Nightbird said:
My guess is MB, because the fans shouldn't go on if PSU is dead.

Any chance of plugging the PSU in question into a working system (nothing expensive k?) and testing it?
Click to expand...

If it's the MB, it shouldn't work flawlessly when plugged into my bench on the UPS....
PSU is clearly not dead, I'm thinking maybe some choke or protection circuit which comes in for low voltages is borked.... then on my clean power here it doesn't need that circuit....
 
Eck, I read it twice and still misunderstood, my bad.

I know some PSUs will tolerate as low as 90v of the 110 normal, do you have a watt meter to measure wall socket power? An EZ Kill-A-Watt will work.
 
I'd measure the supply voltage with a meter both on your bench and at there house to see if there is any difference. In general PSUs preffer higher voltages and anything below 100V is definately suspect and an electrician should be called out to investigate the problem.

Low voltages often mean bad connections and bad connections lead to burnt out wiring and occasionally even fires (though modern self extinguishing plastics make this less common).
 
I will bring my kill-a-watt and test the wall voltage at their place.

I've just never seen a problem like this before. Normally a PSU issue would result in *nothing*, no lights no fans....
Plus, it was working up until last week.

Is there anything else which you guys think could cause this behavior?
 
alexrud said:
Possible motherboard/case grounding issue?
Click to expand...

Potential ground fault in their house?
She says there has been no electrical work recently so I'd be surprised if there's a fault and the PC decided to care about it just now.
 
Well, I tested the PSU and everything checks out.
That pretty much means it has to be their power?

Anybody else have ideas?
 
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