Re: Black screen on boot: MB or PS defect?

Tom McCreadie wrote:
On Sun, 16 Oct 2011 16:35:57 -0400, Paul <nospam@xxxxxxxxxx> wrote:

<snip>
Look in section 3.2 of the P4C800-E Deluxe manual. You can go to
support.asus.com and download a copy from there, if you don't have the
paper copy (with the tiny print).

The first three in that listing are:
ery error No CPU Installed <---- based on CPU grounding a socket pin etc.
You hear this, if powering a "blank" motherboard
fresh from the box, with no components installed.

System Failed CPU Test <---- BIOS code to clear Winbond timer, didn't
get run in time. Most likely reason is that
no BIOS code at all is executing, and it's
just crashed or had a double bus fault.

Thanks. Yes - on renewed, more careful listening, the above "System Failed CPU
Test" was the only error message I was getting. This was irrespective of the
installed/uninstalled combo's of video or RAM. (And to my embarrassment, I'm
now aware that there has already been screeds of Usenet- and web-forum postings
on that specific error message)

Thereafter in my testing, however, at the instant I powered up for the umpteenth
time (with the intention to check out the working system voltages with my
meter), a decisive event occurred: The Antec PS gave a sharp cracking bang,
emitting a small puff of smoke and a burning smell !. Capacitor exploding?

My tentative take then is that an ageing / failing Antec PS was the culprit in
my start-up (and fuzzy screen) problems. But of course, can't rule out that the
troubleshooting régime of frequent on/off power switching may well have
hastened its demise. My understanding is that most Antecs die gracefully, so I'm
crossing my fingers that there will be minimum collateral damage :-).

Anyway, time to pick up a new PS...there's nothing like a small explosion to
help crystallize the thoughts and narrow the choices :-)


"System Failed CPU Test" could be power related, but lots of other
motherboard failures could also do it.

*******

"sharp cracking bang". I bet that got your attention :-)

It also kinda answers your questions as to what is broken.

At least I pulled mine, before that happened. I only got a small
puff of smoke from one of mine, which was probably smoke coming
out of one of the output caps (rather than something on the primary
side).

Hope there is no collateral damage. Time will tell. I think the
odds are in your favor, and still worth buying a replacement supply
and giving it a test.

*******

With regard to the power switch on the back of a PC. It's not meant
for quick toggling. The inrush limiter needs time to cool off, to
operate properly. Rapid toggling (like once a second), is hard
on the switch, amongst other things. The supply draws a huge current
for a cycle or two of 60Hz AC. In some cases (I have a supply here
that does this), it draws enough current to cause the UPS to beep on
overcurrent.

In this power supply schematic, inrush limiting is provided by NTCR1 in
the upper left hand corner. The temperature of NTCR1 changes while
it's running. It has to cool off a bit, so it goes back to the
high resistance state, which helps limit current flow for the first
second or two of operation. I give mine perhaps 30 seconds, before
switching on again. This might not be the only way to build an
inrush limited, and perhaps there are more reliable ways to do it.

http://www.pavouk.org/hw/en_atxps.html

If too much current is jammed through the power switch, it degrades
the contacts. On a product we built at work, we had a whole bunch
of power switch failures, caused by that current flow. In fact,
on the computer at my desk (our own brand of computer), I switched
on one morning, and the switch crumbled in my fingers. The underneath
of it was burned out. Pretty funny, and a good way for the problem
to get some attention :-)

Paul
.