power off problem

  • Thread starter Thread starter Bill Butler
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Bill Butler

I am experiencing odd behavior during power off. The first symptom I
noticed was at the point during the power off sequence when normally
the power would go completely off, the speakers made a noise like
dit-dit-dit-dit in a slowing sequence that finally stopped. The dits
started about 3/sec and ended up about every 2 seconds. This took
about 10 seconds. Since it sounded like something spinning down, I
opened the case, disconnected power to all the disks, and powered up
(of course getting complaints about no system disk) and off. I
observed the same behavior, and also noticed that the fans, which
stopped while the dits were still going, were nudging slightly in sync
with the dits. So it seems like some power is still going out after I
hit the power off. If I physically unplug the computer or turn off
the power supply switch (not the case switch, but the power supply
switch itself on the back), then the noise stops immediately, but
starts again when I plug-in/turn on. This time it doesn't stop until
I cycle the case power again. I'm thinking this may be a power supply
problem or possibly a motherboard problem. I don't know if improper
control is being sent to the supply, or if the supply is misbehaving.
I haven't observed rebooting that might be symptomatic of a failing
supply. I don't have extra power supplies or motherboards around to
test with. Any suggestions? I have an ASUS P4PE motherboard with an
Antec case/power supply. Thanks!
 
I don't think this is a problem. Just ignore it (or turn your speakers
off so you don't hear it on power down).

Power supplies don't just end abruptly when they are turned off. The
switching inductors and filter caps still have energy in them. And once
the voltage output drops to a low level, your system doesn't have much
of a current draw to bleed off this energy. What you are experiencing
is that bleed off. If this didn't cease in the 10 or so seconds you
mentioned then I might start worrying about a bad power supply.

Interestingly enough, this ties into one of those questions that people
ask sometimes: why does the instruction manual or upgrade manual tell
me to turn someting off and wait 30 seconds before powering it back up?
Pretty much it is this same phenomenom, things don't turn all the way
immediately just because the lights went off.

-Jim
 
I don't think this is a problem. Just ignore it (or turn your speakers
off so you don't hear it on power down).

Power supplies don't just end abruptly when they are turned off. The
switching inductors and filter caps still have energy in them. And once
the voltage output drops to a low level, your system doesn't have much
of a current draw to bleed off this energy. What you are experiencing
is that bleed off. If this didn't cease in the 10 or so seconds you
mentioned then I might start worrying about a bad power supply.

Interestingly enough, this ties into one of those questions that people
ask sometimes: why does the instruction manual or upgrade manual tell
me to turn someting off and wait 30 seconds before powering it back up?
Pretty much it is this same phenomenom, things don't turn all the way
immediately just because the lights went off.

-Jim
Click to expand...

You mean the noise will continue for hours in this situation? That'd have
to be something wrong with the 5VSB (Stand By power). I'm no hardware
expert but possibly a bad capacitor in the P/S allowing some AC pulses
through but the rate doesn't umm correlate.
I'm thinking this may be a power supply
Click to expand...

I think the power supply would be the right place to start but first check
the capacitors on the mbrd before spending $$ - apparently the mbrd
capacitor problem is back:
http://www.reed-electronics.com/electronicnews/article/CA6283199.html.
Look for bulging tops or leaking around the bottom - see images here:
http://www.motherboardrepair.com/
 
Thanks for your various thoughts. I have checked the caps on the MB,
and I'm pretty sure I observed no bulging or leaking of any of them.
The pictures were very helpful to show what to look for. I did one
other test at the suggestion of a friend. He thought that if the fan
on the power supply itself didn't 'nudge', that was a clear indication
that it was the MB, since that fan is not powered from the MB.
However, this fan does also nudge. That still leaves me unsure, since
it could still either be the MB giving the PS bad signals, or the PS
itself not doing what the MB tells it. Any other test suggestions
before I try to beg/borrow a PS to test? I'm thinking to try that
first as it is an easier test than trying a new MB.

Thanks again,
Bill
 
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