The cheapie power supply testers will false-good check sometimes simply
because they do not load the powe supply down and simulate a running
machine's demand for energy. A more expensive tester would do so.
-----Original Message-----
From: Personal Computer Hardware discussion List
[mailto:[log in to unmask]]On Behalf Of John Sproule
Sent: Monday, September 24, 2007 1:56 PM
To: [log in to unmask]
Subject: [PCBUILD] Power Supply Malfunction?
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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