On Tue, 25 Nov 2003 23:52:21 -0700, Brian Friedl
wrote:


Kevin Falconer wrote:

I was just given a presario 4764 that had been working but then just quit..
no fan, no boot up, nothing. I installed a new power supply and still nothing.
I'm told the power supply will not come on without a signal from the MB. Anyone
know if perhaps a dead battery supply on the MB would prevent the main power
supply from coming on ? I have a hard time believing I got a bad power supply.
I dont want to dump the computer if perhaps a new battery on the MB will fire
up the power supply, thanks in advance for any comments.

Was this computer working while you had it? It sounds like the
motherboard or CPU has problems. There is a very remote possibility that
it is the battery. However, this signal the SMPS (switch mode power
supply) receives from the MB is really from the SMPS. When you press the
power button on a ATX computer, it requires a working CPU to tell the
SMPS to turn on.

Steps to check:
1. Swap out CPU if possible.
2. Unplug switch from MB and try shorting out the 2 pins on the MB
3. Go get a new computer


It does not require a working CPU tturn on a power supply, in general,
nor memory, battery or other parts installed unless Compaq did
something unusal to the motherboard, which isn't all that unusal for
Compaq.

On the other hand, a CPU or other component that's shorting out could
cause a problem, so any and all questionable parts can be removed from
the motherboard. Considering that this may not even be an ATX power
supply, if it's an AT it can be unplugged from the motherboard
altogether and just plugged into one drive for a power-on attempt, or
if an ATX just ground the PS-On pin in addition to above.

The power supply might be checked to confirm that it's input voltage
switch is set appropriate to the location, but otherwise that system
is better retired for something more modern, standard, and of course,
working.

We might (or might not) be able to help more with a better description
of the system, the motherboard and power supply type, as much detail
about them as possible including the connector type and existance of
external switches. Compaq also sold some systems (don't recall model
numbers) with AT power supplies, having a rocker switch on the back
for the AC input and a switch on the front bezel but the switch on the
front wasn't actually a power switch, was a sleep switch. Those
systems never turned off except by the back switch and I don't think
the user was supposed to turn them off in back, just leave them
running in sleep mode... leave it to Compaq to take perfectly working
standard designs and create a problem.


Dave