cisz said:
Thanks.
I was thinking the sound was coming from the hard drive but after your post
I listened more closely and it seems to be the cpu fan.
I guess the power supply might be going or the power company voltage is
varying.
I wonder if there's an easy way to check the line voltage without having to
wait and watch a volt meter.
Well, the first question I have to ask you, is whether the computer is
set up to vary the CPU fan speed in response to the CPU temperature.
I always set my computers to run the fans at constant speed. And then,
when the fans misbehave, I can blame it on power.
But if you're using some setting intended to maintain a quiet computer,
then the variation could be just compensation for CPU temperature.
Which changes constantly.
With respect to voltages, your power supply is a "regulator", which
means the output stays constant over a pretty wide range of
AC input voltages. You can see pretty significant light dimming in the
room, and the computer continues to run. It might work from 90V to 120V
for example. If you notice the room lights dimming (so it is hard
to read a book), then it might be time to check your AC. We had a
substation failure one winter day, that did something like that -
dropped the voltage, a lot. Even traffic lights were running
half intensity.
You can pick up one of your Molex 1x4 drive connectors, and *carefully*
probe the 12V there. Remember, that if you short the shiny metal
of the two probes together, the power supply will throw some pretty
big sparks. And you could damage something on the computer by
doing that. One thing I do, is use one alligator clip on the black
multimeter lead. I clip the lead onto an I/O screw in the I/O plate
area on the back of the computer. That gives me a ground connection.
Then, holding only the red probe in my hand, I'm free to read out
the 12V on the Molex 1x4 drive connector. That should be a safe way
to check your 12V rail. I find the multimeter is more accurate,
than the hardware monitor chip that gives voltage numbers in the
BIOS.
A basic spec for a power supply, would be +/- 5% tolerance. The
variation really shouldn't be that large, if the thing is healthy.
I treat "wandering" of that voltage (i.e. doesn't seem to be
the load variation that is causing it), to be an indication
that the supply isn't healthy. Whether you replace it
right away, is up to you. I don't have any examples of how long
it lasts from first noticing "wandering", until it dies. Since
a lot of modern supplies die quietly, without killing something,
it might not be a big deal to continue using it. But if it
was a Bestec 250W, which typically blows out the motherboard,
I'd replace that the first day it farted. So check into the
history of that brand/model of supply, and see if it has done
a lot of damage or not.
Paul
