On Wed, 21 Jan 2004 17:41:00 GMT, "techforce"
wrote:

Apparently, you have not been inside a PC Power Supply and worked on them,
else you would know this is quite the opposite unless the AC protection in
the design of the PS has been degraded or is non exsistent. Most Failures I
have worked on have the AC Protection still in Tact but other components
Fail.

I would like to hear JBR say "Yes, I checked the keyboard power
jumper." It may not seem a logical cause for repeated power supply
failure, but that is what actually happens. Until I discovered this
one computer would lose its power supply within two weeks, in one case
the supply lasted about a minute. I finally read the manual,
discovered the jumper, and the system has lasted since 2000. In
another case a store-built clone was losing supplies, when the second
one failed he brought it to me, sure enough keyboard power was
enabled, changed the jumper, and no more failures. Yes using better
supplies would help, but only to provide enough standby current.
That's why I'm chipping in with this suggestion, it doesn't appear
that others in this thread have encountered this issue, or have, but
don't know it.

Step one, check for this jumper, if it exists even, and assuming it's
a PIII, THEN move on to incoming AC. Logical?

Also I don't find that the supplies "degrade" usually it's the zener
shorting, a resistor overheating, or some such.

. STeve ..

Dirty AC actually causes Components inside the PS to 'degrade' more than
actually burn out, which in turn can disable partially or fully the overload
DC protection or alter the Regulation so that the Mobo is Getting less or
more than 12/5VDC with unregulated current. Its possible in some cases users
will not know somethings wrong, continue to use the Degraded PS, and damage
the MOBO.

Its also possible someone could detect the problem earlier because sometimes
the PC will have trouble shutting down or give other errors, and be led to
the PS as the cause.

I dont see how a constant Draw on that 12V Line for KB power - given a
**PURE CONSTANT SOLID AC** source , could be such a concern unless the PC
is on 24/7/365.....which may or may not be the case. Even then , if the DC
output were stressed by the MOBO the Shut down circuits would kill the D C
Power output, and the PS will Still have AC power Applied, and technicly be
partially in use. unless of course, Internal Components of the PS have
Degraded, as previously mentioned.

The KB power is really a Long Term effect on the Condition of a PS, side
its only effecting the DC side of the PS. All it could ever hope to do is
shorten the Expectancy of components in the DC circuitry. With only 5 or 12
Volts or less theres not a whole lot of damage that can be done if a problem
were there in a short time as opposed to on the AC side. Higher AC voltages
cause more damage in the Same time than Lower DC ones will.

Your experience by disabling the Jumper in effect took away power from the
PS DC side, which in effect reflects back to the AC side regardless of what
the Motherboard wants to do. Its unlikely 2 or 3 PS's would burn out in the
Same Way if there was a problem on the MOBO. They usually will shut down a
PS if the protection circuits are still working. But if those PS's were all
run on the Same DIRTY AC Power Source, then you have 3 Degraded PS's , and
are just looking at the symptom than the cause.


I've repaired and built hunderds of computers, and this has been the
only situation I've ever encountered which caused multiple power
supply failures. While dirty AC is a worry, it's more likely to cause
damage to the MB than to the power supply.