Hi Robert,
Every PC-PSU has a currentlimiter circuit that will shut down the
PSU in case of currents (or voltages) that exceed the limits of it's specs
by some margin.
Most PSU also have a temperature protection that shuts down the
PSU in case the driver transitor(s) get too hot. In your case I suspect that
one or more of these transitors went bad and that the PSU-temp limit
kicks in with everything but the smallest load because they/it are/is already
hot when no load is drawn.
Once this protection kicks in you will have to switch off the mains power
to reset the PSU. So removing the load as you've described will not
bring the PSU back to a low-load working mode.
IMHO ... Either this is a very "small" PSU or this PSU is defect!
Normally a PSU only works with a minimum load of say 0.5 Amp _at_ 5V
So I use an old defunkt harddrive as a minimum load to test the PSU
Advise:
Work out the maximum load that still lets the PSU "work" and measure the
voltages on one of the drive-leads. An old (obsolete) 3.5 floppy drive
might be a good test load.
The voltage across the black-red connector should be ~+5V
and across the yellow-black connector should be ~+12V
If things are no longer in this range than consider it a dead PSU
Even if these voltages are in this range it may be defect but at least it
will not kill off any of your other equipment while trying .......
Consider that opening up the PSU and frolicking around in it may pose
a risk to your equipment and to your health........ ;(
If you don't know what you are doing get somebody who knows....
or buy a new PSU. After all, they are not that expensive nowadays
Or look in a thriftshop for a good second hand.
regards
Sipke de Wal
-------------------------------------------------------------------
http://xgistor.ath.cx
-------------------------------------------------------------------
----- Original Message -----
From: <Demon02554_at_aol.com>
To: <classiccmp_at_classiccmp.org>
Sent: Monday, May 14, 2001 4:05 AM
Subject: gimpy (not broken) PSU
> ok...this one is weird
> it is a standard PSU in a 486 Compaq that i just dug up outta my dads
> storage...
> it will start up only if i disconnect it from everything...
> when i connect it to the motherboard and only the motherboard then it will
> start for a few seconds, then die...and even if i disconnect everything from
> it after that it won't start back up...
> before i go through and test every connection does anyone have any
> suggestions as to what is wrong with this thing?
>
> thanks,
> Robert Cobbins
Received on Mon May 14 2001 - 17:39:59 BST