Interesting power problem

[Man-wai Chang to The Door (33600bps)]

I have a PC with an Antec TruePower 550W. Tonight when I tried to power
it on via the power button, it didn't respond. I then un-plugged two
DMB-TH USB HDTV Tuners, it could then be powered on!

I powered off the PC right after the BIOS screen. Then I powered it up
again with both USB HDTV Tuners plugged in. It booted!

Why? Were the 2 USB devices drawing too much power? Or what? Or was
there something wrong inside the power supply?

--
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[Paul]

I have a PC with an Antec TruePower 550W. Tonight when I tried to power
it on via the power button, it didn't respond. I then un-plugged two
DMB-TH USB HDTV Tuners, it could then be powered on!

I powered off the PC right after the BIOS screen. Then I powered it up
again with both USB HDTV Tuners plugged in. It booted!

Why? Were the 2 USB devices drawing too much power? Or what? Or was
there something wrong inside the power supply?

The tuners could be drawing power from +5VSB, and you might have
overloaded or overheated the regulator on that rail. (+5VSB is the
rail that runs when the computer has been shut down in Windows.)
Many modern motherboards don't offer jumper options to change
that. On older motherboards, you could change a USBPWR jumper, to
move the load to the +5V rail instead.

When the fan is spinning on the supply, perhaps the extra cooling
is enough to keep it running. That might be why you managed to start
it later.

Power supplies have around 2 amps to 3 amps of current on +5VSB,
and normally that would be enough. But if you're powering a lot
of 500mA USB loads, you might be exceeding that limit. The motherboard
itself may draw 1 amp while the computer is shut down in Windows.

As for the supply, the problem could also be related to bad
capacitors inside. It all depends on how old the supply is.
I have had one Antec supply (built by ChannelWell CWT) that
failed due to bad capacitors.

But only open up the supply, if the warranty has expired. The
Antec supply would normally have a sticker placed over top of
one of the screws that keeps the top on the supply. Removing
that screw and tearing the label, voids the warranty. If the
supply is already out of warranty, then you can open it for a
look. (Unplug the supply before working on it!) You don't need
to touch or poke anything inside the supply - all you need
to do, is check for bad capacitors via a visual inspection.

http://upload.wikimedia.org/wikipedia/commons/8/84/PSU_Caps.jpg

The rust colored deposits on some of the capacitors, show the
ones that have failed. The large capacitor in the middle of
that picture, is bulging on top, and is also failing. The
tops of the capacitors should be flat - the bulging means
gas pressure is building up inside and eventually the
capacitor will vent and leak.

Paul

 

[Man-wai Chang to The Door (33600bps)]

Power supplies have around 2 amps to 3 amps of current on +5VSB,

and normally that would be enough. But if you're powering a lot
of 500mA USB loads, you might be exceeding that limit. The motherboard
itself may draw 1 amp while the computer is shut down in Windows.

Maybe the two HDTV tuners really draw a lot current....

Thanks!

--
@~@ Might, Courage, Vision, SINCERITY.
/ v \ Simplicity is Beauty! May the Force and Farce be with you!
/( _ )\ (x86_64 Ubuntu 9.10) Linux 2.6.34
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