psu auto switch off - why?

David Cole · Post by **David Cole** » Sat Jun 21, 2003 6:29 am

So keen is my Zalman 400w psu not to cause me any additional noise it has taken to switching itself off during boot up. The boot up gets as far as the first XP splash screen then the power dies. The Zalman is not modded in any way.

When I switch the power on again there is always a perfectly normal boot followed by completely normal operation.

There are three case fans - 92mm Panaflos on Zalman Fanmates covering cpu and gpu with Zalman heatsinks, and an 80mm Papst blowing cool air into the Zalman psu from front top.

This has only just started happening and I can't think of anything I have done to cause it but problems usually are pilot error so I am quite ready to find out that inadvertently I've done something wrong.

Grateful for any ideas as to why this might be happening and what I can do about it.

Post by **MikeC** » Sat Jun 21, 2003 8:16 am

bizarre. 1st suspect is Windows, just because Gates should be blamed first for anything -- for becoming the richest man on the planet while selling lousy products.

How about if you go into the BIOS setup menu during the first boot? Does tghe PSU remain on? If so then my first cxomment holds again...

Really hard to say more till you fool around a bit more & and tell us a few more symtoms.

David Cole · Post by **David Cole** » Sat Jun 21, 2003 12:06 pm

Thanks.
I'm stumped.
I tried re-booting a few times...with no problems.
Switched off and left the pc for a couple of hours. Powered up again and went straight into the BIOS and hung around there for a while...no problems...then went into XP...normal boot up, no problems.
Just have to try going into the BIOS first on every power on for a while to see if I get any self-power down. If I don't, that'll either mean its a software problem or the hardware problem has gone into hiding.

I assume that the psu is occasionally getting a message from somewhere during the software loading to power down for some reason.
I don't know what would cause the mobo to send this message. Bit of a mystery.

Not much point in putting in a different psu yet.

dukla2000 · Post by **dukla2000** » Sun Jun 22, 2003 3:54 am

3 thoughts:

1) The psu could shut down if there is any error on the output lines (e.g. short circuit). It may be in those first seconds it is getting some crazy load/voltage that confuses it (that would be a bugger to trace if going to BIOS first avoids the problem, as MikeC suggests something about how Win is loading drivers)

2) The mobo may be dropping the PWR-ON signal - check your power button for loose connections.

3) Your mobo may have CPU overheat circuitry that is able to shutdown, and is now playing up?

Very much thoughts - the fact it can power on and run fine means I am only musing the above 3. Neither convinces me but are thoretically possible.

David Cole · Post by **David Cole** » Sun Jun 22, 2003 11:02 am

Thanks everyone. I wonder if dukla2000 might be on to something in his 3).

This is going to sound daft, and it doesn't quite match the facts, but I wonder if my moving the panaflo 92mm very slightly - about 25mm - to cover better the cpu Zalman flower might have done the trick. The cpu temps came down a couple of degrees after I did this and is it possible that the cpu temp sensor needed just a little more air/cooling at start up or would switch itself off? Why it would re-boot ok I don't understand.

Anyway, so far still so good....