Hi all! I have a hardware problem here, but can't figure out
whether the problem is the power supply or the motherboard. Either
way, I'm aware something is very wrong and I'm already shopping for
a new system. However, if this one can be repaired inexpensively
enough I'd like to keep it as a second system.
This is a bottom-end Compaq desktop tower. Once it's powered up, it
keeps working as well as ever. The problem is powering it up. When
my UPS is turned on or the AC cord is plugged into the tower, the
LED on the back of the power supply that's supposed to be on
whenever there's AC flashes quickly, and a faint "tick" is audible
each time it flashes. The tower does nothing else; it doesn't even
start to spin the power supply fan. Once AC power is removed, the
LED gradually flashes more slowly until it stops completely, which
takes 30-60 seconds.
The first time this happened was two weeks ago, and somehow after a
few hours the problem, whatever it was, "fixed" itself. This past
weekend I powered it down for the first time since then, and it did
not power up at all. During that time, I used my DMM to measure one
of the peripheral power connectors (the kind that would power a PATA
drive), and discovered that when AC is applied, the +12V line rises
within about half a second to about 0.67V and stays there. When AC
is removed, that voltage gradually drops to zero as the LED flashing
slows down. When the +12V line is steady at about 0.67V, the +5V
line is steady at about 0.27V.
What I discovered yesterday was that if I disconnect the power
supply from the motherboard (just the 20-pin power connector, not
the case fan power or any other power connector), apply AC (at which
point that LED comes on steadily), and /then/ attach that 20-pin ATX
motherboard power connector, the system then powers up normally and
runs. (Yes, I already know I'm not supposed to touch that while
power is on!)
Obviously something is very wrong here. My question here is, is it
more likely that the problem is the power supply or the
motherboard? (Either of which I can replace myself.) Or could it
be something else that I haven't considered? This system also seems
to go through about one internal DVD burner per year, but I don't
/think/ that's related. Can any of you hardware experts suggest
anything? Thanks VERY much in advance!
Adam
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