The bad p/s is putting out the correct voltage, but not enough amps -

Tony Mayer



John Sproule wrote:
> I was looking at a Dell 4500.  The owner rarely shuts this system down, 
> but after she did shut it down, the other day, she was unable to get it 
> to turn back on.  The power-on light, built into the on-off button, 
> would glow, but no other signs of life when the power button was 
> depressed.  When I opened the case, I could see that the light on the MB 
> would come on, when the power supply was plugged in, indicating stand-by 
> power to the MB, but no fans would spin when the power button was 
> pushed.  The diagnostic LEDs at the back of the MB showed no activity 
> either.
> 
> Testing the power supply with a one of those little power supply 
> testers, the power supply seemed ok.  It's fan would spin and all the 
> little lights on the tester lit up indicating the various power rails.
> 
> I ended up swapping around power supplies, anyway, and I found that a 
> different power supply would power up this Dell.  Conversely, the Dell's 
> power supply wouldn't power up a known working system.
> 
> I know that these inexpensive power supply testers aren't very 
> sophisticated, but I was curious as to how this power supply could show 
> up as working when tested, but still be unable to boot up a computer.  
> The only guess that I could come up with was that perhaps the power good 
> signal comes up too slowly, now, for the motherboard to accept it.  (The 
> tester indicates a power good signal.)  Anyone else seen this and/or 
> have any thoughts as to what the problem might be?
> 
> Thanks,
> 
> John Sproule
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> 
> 

         PCBUILD maintains hundreds of useful files for download
                     visit our download web page at:
                  http://freepctech.com/downloads.shtml