power supply question, ATX

[-Alby Hewlet]

If I got the right dope from the net, pin 8 on an ATX power supply
is supposed to read +5 vdc if the PS's output voltages are within
specs, and drop to zero if they aren't.

I have one on the bench now and pin 8 is low, but all the other
pins read what they shuld.

My question is, do they always read low if you have them out
of a system sitting on a bench with pins 13 and 14 jumped?

or do you have to test them installed?

Thanks,

Al

 

[ric]

If I got the right dope from the net, pin 8 on an ATX power supply
is supposed to read +5 vdc if the PS's output voltages are within
specs, and drop to zero if they aren't.

I have one on the bench now and pin 8 is low, but all the other
pins read what they shuld.

My question is, do they always read low if you have them out
of a system sitting on a bench with pins 13 and 14 jumped?

No. See:

http://www.formfactors.org/developer/specs/ATX12V PSDG2.0 Ratified.pdf

Section 3.3.1 and Figure 6.

 

[-Alby Hewlet]

thanks ric,
the link has everything! Some of it is beyound me. I'm a screwdriver and
vom guy, if you know what I mean.
Anyway, I set up a system on the bench and measured all the voltages, and
they are all ok. The one that was
low, was at 4.6 Vdc when plugged into the board. But, it still doesn't
boot. When I keep re-cycling it on and off,
every once in a while it'll boot.
Swapping out a known good PS, that measures almost exactly the same,
volatage wise, it boots everytime, so
I know there's something in the power supply that's fishy, but I havent'
been able to figure out what. It's not heat
related because after it's been plugged in for 5 minutes or so, so it's at
operating temp, it'll boot maybe once
every 5 or 6 times, same as when it's cold. It isn't anyting loose on the
board because I'm recycling it by shorting
the pw pins on the mobo with a fork handle, i mean, I'm not moving anything.
There isn't anything loose, ie, by tapping it, the symptoms don't change.

Suggestions?

Al

 

[JAD]

how many sticks of memory? remove one if applicable. boot a few
times.......

 

[-Alby Hewlet]

Hi Jad,
one stick of 128megs. I tried 2 other 128's and one 256, and
got the same results so I ruled out memory.

 

[ric]

thanks ric,
the link has everything! Some of it is beyound me. I'm a screwdriver and
vom guy, if you know what I mean.
Anyway, I set up a system on the bench and measured all the voltages, and
they are all ok. The one that was
low, was at 4.6 Vdc when plugged into the board. But, it still doesn't
boot. When I keep re-cycling it on and off,
every once in a while it'll boot.

What's at 4.6v ?? The PWR_OK ??

Swapping out a known good PS, that measures almost exactly the same,
volatage wise, it boots everytime, so
I know there's something in the power supply that's fishy, but I havent'
been able to figure out what.

Probably a timing issue. The PWR_OK line must rise within the time
guidelines given on that drawing.

Does your case/MB have reset capabilities?

 

[-Alby Hewlet]

What's at 4.6v ?? The PWR_OK ??

Yes, pin 8, gray wire, power check voltage.

Do you think shorting it to pin 9 is a good idea?

Probably a timing issue. The PWR_OK line must rise within the time
guidelines given on that drawing.

.... hmmm.... how do you adjust the timing?

Does your case/MB have reset capabilities?

Yes, and shorting the reset pins reboots it.

 

[ric]

Yes, pin 8, gray wire, power check voltage.

Do you think shorting it to pin 9 is a good idea?

NO! Don't do that! It's a TTL level signal. Anywhere from 2.0-5.0 is OK.

... hmmm.... how do you adjust the timing?

An R/C circuit inside the PSU. Not really adjustable without a scope.

Yes, and shorting the reset pins reboots it.

Sounds more and more like a timing issue with the PWR_OK circuit in
the bad PSU. Either send it in for repair or toss it.

 

[-Alby Hewlet]

Hey Ric,

Thanks for taking the time to walk me through this. I guess I'll give up on
using in a computer. I think I'll just use it as power supply to run other
things. Can always use 12 volts somewhere.

Alby

 

[ric]

Thanks for taking the time to walk me through this. I guess I'll give up on
using in a computer. I think I'll just use it as power supply to run other
things. Can always use 12 volts somewhere.

OK, but the PWR_OK interface is a strange one. That PSU may well
work fine with another (not so strict) motherboard.

Good luck!

 

[-Alby Hewlet]

Hey Ric,
Your just full of good ideas.
I'll try with a different mobo and see what happens.
I never thought of that!
Thanks,
Alby

 

[ric]

Hey Ric,
Your just full of good ideas.
I'll try with a different mobo and see what happens.
I never thought of that!

Let me know the result, OK?

 

[-Alby Hewlet]

It worked!

I have an old P2 450 system I use for a back up so I swapped out the power
supplies and the "bad" one fired it up perfectly. This is great. Anytime I
can re-cycle anything and keep it out of a landfill is a net gain for all of
us.

Thanks again for that idea!

Alby

 

[ric]

It worked!

I have an old P2 450 system I use for a back up so I swapped out the power
supplies and the "bad" one fired it up perfectly. This is great. Anytime I
can re-cycle anything and keep it out of a landfill is a net gain for all of
us.

Thanks again for that idea!

Alby

Congratulations! Told ya that PWR_OK circuits were fickle.

Now to figure out once a week BSOD occurrences....