Power supply random failure

  • Thread starter Thread starter Niklas
  • Start date Start date
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Niklas

Hello.
I have a powersupply q-tec dualfan gold 400W that that shuts down
completely randomly. When I try to turn on the computer it doesnt
start, then I have to disconnect the powercord and connect it again
and voila! the pc turns on when pressing the on button on the atx
tower.

I bought it separately less than a year ago and I have a guarantee but
the shop says I have to leave the entire computer for repair but I
cant really do that.

In the bios settings all tempguards are disabled and the temp is about
40-50 degrees celcius all normal.

All power cords in the computer are connected inlusive the 12V cord
and extra fan.

This is my setup:
Abit motherboard VT7 with LAN
Pentium4 3.0ghz 512 cache northwood
Dual DDR 2x512mb
HDD 180gig
Soundblaster Audigy
ATI radeon 9200 128mb
Nec 2500 DVD rw
floppy

Please help!
Niklas
 
Niklas said:
Hello.
I have a powersupply q-tec dualfan gold 400W that that shuts down
completely randomly. When I try to turn on the computer it doesnt
start, then I have to disconnect the powercord and connect it again
and voila! the pc turns on when pressing the on button on the atx
tower.
Click to expand...

Usually when I fix one of these it isn't a bad PSU, but a failing mainboard.

Take a CLOSE look at the capacitors, especially around the CPU, for any that
are swollen on top or have brown goo underneath of them.

Your machine sounds new enough not to have this problem, but it doesn't hurt
to check.
 
Hello.
I have a powersupply q-tec dualfan gold 400W that that shuts down
completely randomly. When I try to turn on the computer it doesnt
start, then I have to disconnect the powercord and connect it again
and voila! the pc turns on when pressing the on button on the atx
tower.
Click to expand...

It is junk, just replace it by whatever means necessary.

I bought it separately less than a year ago and I have a guarantee but
the shop says I have to leave the entire computer for repair but I
cant really do that.
Click to expand...

Is that in writing? I mean, did they specify this as a term of
warranty when you bought it?
If not, flat out refuse this and demand the warranty be honored.
You are not required to submit to this for a single-item purchase
otherwise... warranty was on the single item, yes?

Except, you might only be entitled to replacement of same junk
q-tec brand, so aim for getting credit towards a good name-brand
instead. $20 credit off price of decent name-brand might be
better than new q-tec, unless you feel like eBay-ing the new
replacement to recover the loss.

In the bios settings all tempguards are disabled and the temp is about
40-50 degrees celcius all normal.

All power cords in the computer are connected inlusive the 12V cord
and extra fan.

This is my setup:
Abit motherboard VT7 with LAN
Pentium4 3.0ghz 512 cache northwood
Dual DDR 2x512mb
HDD 180gig
Soundblaster Audigy
ATI radeon 9200 128mb
Nec 2500 DVD rw
floppy
Click to expand...

Shutdown means that it turns completely off?
Check bios for a shutdown temp and raise that temp if present.
It might be good to take voltage readings with a multimeter if
you have one. Explain to shop that system cannot be allowed to
suffer downtime, tell them something like "that's why I bought
power supply separate with warranty".
 
To me it sounds like you're mainboard is failing.
Although, to test you're psu you could bridge the green and black wire on the
ATX motherboard connector, it should run while not being connected to the board.
 
To me it sounds like you're mainboard is failing.
Although, to test you're psu you could bridge the green and black wire on the
ATX motherboard connector, it should run while not being connected to the board.
Click to expand...

Often I find power supplies that are beginning to fail or are of
insufficient capacity for the intended system, would still turn
on and run fan and a drive if disconnected from rest of system...
it's not a test that can determine if a PSU is ok, only if it's
dead (if there were no sign of life from it). Voltage readings
of PSU output can be revealing, but PSU must be hooked up to the
system or very similar load while readings are taken.
 
Hello.
I have a powersupply q-tec dualfan gold 400W that that shuts down
completely randomly. When I try to turn on the computer it doesnt
start, then I have to disconnect the powercord and connect it again
and voila! the pc turns on when pressing the on button on the atx
tower.

I bought it separately less than a year ago and I have a guarantee but
the shop says I have to leave the entire computer for repair but I
cant really do that.

In the bios settings all tempguards are disabled and the temp is about
40-50 degrees celcius all normal.

All power cords in the computer are connected inlusive the 12V cord
and extra fan.

This is my setup:
Abit motherboard VT7 with LAN
Pentium4 3.0ghz 512 cache northwood
Dual DDR 2x512mb
HDD 180gig
Soundblaster Audigy
ATI radeon 9200 128mb
Nec 2500 DVD rw
floppy

Please help!
Niklas
Click to expand...

Unless you have some previous electronics repair experience your
chances of fixing it are slim . . .

The leaky electrolytic cap thing should be checked as one responder
mentioned.

There is usually an independent "Over Voltage Protection" circuit in
the PS. This will monitor critical voltages and "crowbar" (short out)
the output if a monitored voltage rises too high. (too high can
damage the rest of the system)

The crowbar circuit is usually just an SCR (silicon controlled
rectifier or thyristor) across the 5V supply (all the others are
usually derived from the 5 or 3.3 or whatever the "logic" supply
voltage is)

A lightly loaded supply can cause problems if the load is less than
the PS minimum (allowing the voltage to rise). This is very rare . .
.. but can happen. A loose connector to the MB will cause this problem
though since the load is briefly removed and the supply can rise too
high triggering the OVP.

The more likely culprit is something like a transient noise spike
triggering the OVP into conduction. Once conducting SCR's don't stop
unless the current drops below a low threshold.

What may be going on is the OVP kicks in, shorts the supply, and the
"Over Current Protection" circuit keeps it from blowing fuses while
keeping the SCR in conduction. Shutting off the supply allows the
current through the SCR to drop below its threshold and the short is
removed.

Modern computers may not "shut off" completely. They just go into
hibernation as long as the mains voltage is present.

The supplies, as a rule, are well filtered to ignore transient
voltages (lightening strikes, electrically "noisy" loads on the same
power line, etc..) Try a different outlet, different location, etc..

There is always the slim possibility that a peripheral is injecting
noise and causing problems.

Always the possibility that the trigger circuit for the OVP is a
little too sensitive or set too low, or just flaky.

A lot of things can cause your symptoms, it usually takes knowledge,
experience and test equipment to troubleshoot electronic problems.

See if they can give you a "loaner" power supply as a way of
eliminating the supply itself as the culprit. Assuming the computer
is "mission critical" and can't be taken out of service for repair.
 
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