About three weeks ago my power supply went out on my Asus mobo (p4s533 or
something like that). The asus mobo had a 4-pin cpu power connector from the
psu going to it. Well I had a spare psu that had no such 4 pin cpu connector
but I put it in anyway and the computer ran just fine.
Sometimes this will work,when the motherboard ties the 12V
lead on the ATX 20/24 pin connector to the CPU VRM
subcircuit input (where the 4 pin connector is).
As processors began to use more and more current it became a
issue and more prudent to prevent a system from being able
to run like that, rather to require having a separate input
for 12V that is not *common* to the 12V lead on the ATX
20/24 pin connector.
When one does try to run a system as you have, it is good to
measure the 12V level at that 20/24 pin connector, and at
the input to the VRM subcircuit - particularly if the ATX
20/24 pin socket is a fair distance away across the board it
may account for a significant voltage drop.
It's been running
fine for almost a month. Yesterday I turned comp on and got the "no signal"
display on the monitor, which suggests a cpu or psu problem to me.
So far we can only conclude the system is failing to post.
Systems being as complex as they are there are many many
possible culprits but the two most commonly at fault (though
you can only play odds for awhile before you lose) are
motherboard or PSU. CPU is hardly ever suspect, only when
there was an obvious problem with it already such as the
heatsink falling off, or if it ran for quite awhile without
the fan working (though in this case a P4 generation CPU
should downclock itself then shut off, not fail from this
slower thermal rise resulting from a fan failure).
The mobo
does not beep when powered on either.
Does the PSU remain on, fans and HDD spinning?
No, nothing wrong with video card or
hdd.
I take it you mean that you have tested these in another
system and this is how you know they still work?
I need to know what, if any, damage could had been caused to the cpu by
not running the 4 pin power connector to it?
For the time being, assume it is not the CPU because the
answer is that there is no direct damage from that, though
extreme current swings could wear out the board, in theory.
In practice you may have a board that failed regardless of
this lack-of-4-pin-connector, or some other cause.
For example when a PSU doesn't have the 4 pin connector, one
that old tends to be optimized for more current on it's 5V
rail, less on the 12V rail. Continually running a PSU at
peak output on a rail as you may have done would tend to
wear it out fairly quickly. You might disconnect AC power,
open the PSU and inspect it for failed capacitors.
You might also use a multimeter now to measure the voltage
Seems to me if there was a
problem, it just wouldnt boot, sort of like now
But it did run fine for
three weeks without the connector, so I don't get it.
Some failures happen immediately and others happen by
putting a lot of stress on something over time... with a PSU
it is a bit like burning a candle at both ends with it
turned sideways, you may get more continual output than the
manufacturer intended, but it won't last nearly as long.
A link to the pic of the 4 pin connector is below if you need to know for
sure what I am talking about.
http://i10.tinypic.com/29kwduq.jpg
Inspect the motherboard for failed capacitors as well, and
unless you see a fault it would be good to try a known
appropriate PSU next... you don't mention # of HDDs or the
video card model (it is always good to include a concise
list of all major parts in a system) but generally speaking
I would aim to use a median to better name brand rated for
at least 18A on 12V rail, even better if it can be confirmed
working first on another system.
Also inspect the contacts, especially that yellow 12V lead
on the PSU connector, and the corresponding socket hole on
the motherboard ATX socket - through overcurrent it may have
heated that up, degrading the connection and possibly even
melting or charring the plastic around it. Such a problem
would easily be visible with a strong flashlight if you have
straight line-of-sight into the board power socket.
You didn't mention the specific PSU make, model and wattage
(and in this case the rating for amps on 12V rail too)
either, this would be particularly useful when trying to
assess how appropriate it was.
It is possible to use a PSU without the 4 pin connector, a
few older PSU had reasonably good 12V rail current
capability but in those cases it is best to use a 4-pin
molex adapter from the existing PSU leads to the 4-pin 12V
input socket on the motherboard. Actually with more modern
systems it is not only best but usually necessary, most
newer boards simply won't run at all without that 4 pin
connector receiving 12V directly.
Anyway I'd suspect the PSU as primary suspect, or if the
board had failed I would tend to blame the PSU for
contributing to it's demise and replace both... so you might
as well get a replacement PSU first if none of the above
seems to help.
Also try clearing CMOS, and check the battery voltage - some
boards won't post once the battery has drained too far
rather than just losing saved settings.
