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From: Brian Downing on 14 May 2010 06:47

I came into my office and smelled that familiar smell of burning
electronic components. I had previously had issues with the graphics
card so I assumed that was the trouble and swapped in a spare; nope.

Power supply was an old Ultra Fryes "rebate freebie" so I figured that
was next most likely suspect and swapped in a new PS; Nope, still out.

Finally took the time to hook up a PC speaker to count beeps and a
audio speaker to listen to the boot error msg (unintelligible little
person in can). Looking through BIOS I checked the PC health and
noticed it was missing +12V, multimeter says P.S. is ok, so I'm
at a loss. Where's that +12V going and is it worth salvaging this
board? I've got many "functional" applications installed as this was
my one XP box so short of fixing this mobo my next best solution is
buying an ebay replacement.

No caps show signs of leakage or damage.

Are there any common components that fail that have this symptom?

Thanks for any insights
From: Rob on 14 May 2010 11:35

"Brian Downing" <bsd(a)panix.com> wrote in message
news:yrak4r6bvzh.fsf(a)panix3.panix.com...
>
> I came into my office and smelled that familiar smell of burning
> electronic components. I had previously had issues with the graphics
> card so I assumed that was the trouble and swapped in a spare; nope.
>
> Power supply was an old Ultra Fryes "rebate freebie" so I figured that
> was next most likely suspect and swapped in a new PS; Nope, still out.
>
> Finally took the time to hook up a PC speaker to count beeps and a
> audio speaker to listen to the boot error msg (unintelligible little
> person in can). Looking through BIOS I checked the PC health and
> noticed it was missing +12V, multimeter says P.S. is ok, so I'm
> at a loss. Where's that +12V going and is it worth salvaging this
> board? I've got many "functional" applications installed as this was
> my one XP box so short of fixing this mobo my next best solution is
> buying an ebay replacement.
>
> No caps show signs of leakage or damage.
>
> Are there any common components that fail that have this symptom?
>
> Thanks for any insights

The PC is basically working then (you say you have accessed the BIOS
and looked at the hardware monitor screen.) Ignore that 12V reading
from that for now, as your PC wouldn't even get that far if +12V was
missing.
I assume then that XP is failing to boot. Any error messages?
What do you actually see on the screen?
--
Rob


From: Paul on 14 May 2010 11:45
Brian Downing wrote:
> I came into my office and smelled that familiar smell of burning
> electronic components. I had previously had issues with the graphics
> card so I assumed that was the trouble and swapped in a spare; nope.
>
> Power supply was an old Ultra Fryes "rebate freebie" so I figured that
> was next most likely suspect and swapped in a new PS; Nope, still out.
>
> Finally took the time to hook up a PC speaker to count beeps and a
> audio speaker to listen to the boot error msg (unintelligible little
> person in can). Looking through BIOS I checked the PC health and
> noticed it was missing +12V, multimeter says P.S. is ok, so I'm
> at a loss. Where's that +12V going and is it worth salvaging this
> board? I've got many "functional" applications installed as this was
> my one XP box so short of fixing this mobo my next best solution is
> buying an ebay replacement.
>
> No caps show signs of leakage or damage.
>
> Are there any common components that fail that have this symptom?
>
> Thanks for any insights

So if we review your symptoms:

1) Looking through BIOS... it was missing +12V

You're telling us the system is running. So far, no visible
signs of trouble, except an anomaly in the hardware monitor.

2) smelled that familiar smell of burning

Something failed. Use nose and eyes, and have a sniff around.
If you're lucky, enough burning smell will be left to identify
the source.

When I had a power supply fail here, the smell was coming from
the power supply itself. I opened the supply and could immediately
see the bright orange-rust colored deposits on top of the capacitors.
I was hit by the "bad cap" problem.

I have a P4C800-E Deluxe (backup computer, not used much),
These are the power numbers, as measured on the main connector,
from when I first built it. These numbers were captured while
running various benchmarks (flat out, using four DIMMs).

ATX12V 5.6 amps
3.3V 14.4 amps
5.0V 0.57 amps
12V_mobo 0.43 amps

The 12V_mobo powers the fan headers mainly. It shouldn't really
be going much of anywhere else. My video card happens to pick up
some 12V, but through an auxiliary Molex 1x4 connector on the
end of the card. I don't think my video card is drawing any of
my 12V in the measurements above. It comes over the aux connector.

There is a GD75232 ("true" RS232 driver) chip on the board, and
that is likely to use +12V and -12V, to make nice looking RS232
signals. That would be a relatively minor load. Some other kinds
of RS232 chips, use charge pumps for that, and can use lower
voltage rails.

The 12V reading in the BIOS, could be connected to the same rail
as is used for fan headers. Be very careful testing around fan
headers with your multimeter. Also, don't try plugging fans
into the header "on the fly" - that caused my board to reset,
the first and only time I tried that.

The fan headers are not fuse protected. If a fan fails short
circuit, a copper track on the board may burn. Other users
have reported fan power track failures, based on no longer
getting power on any header. That can happen to any brand/model
of motherboard.

The P4C800-E onboard regulation circuitry, consists of a chain
of linear regulators to power chipset and DIMMs. That accounts
for the load on 3.3V. Part of my load could be 3.3V feeding the
video card, so YMMV.

That is about all I can contribute. The 12V single wire on the
motherboard powers fan headers, and on that specific motherboard,
the RS232 chip.

The smell could be inside the PSU. The smell could be a fan
failing (taking out the motherboard 12V track as well). The smell
could be a pin on the main ATX connector getting burned. Pull the
main connector and check for damage. The contacts should all be
shiny, on both the motherboard end and the PSU end. A burned pin,
can be caused by bad contact (going ohmic), or by an overload
which was not flagged by the overcurrent protection in the supply.
Overcurrent is set at such a high level, a lot of hardware can
burn, before the PSU says it's had enough. Overcurrent really
only works, for good solid shorts.

The motherboard monitor has to pick up the 12V somewhere, to test it.
If it picked up 12V at the end of the copper track distributing
power to the fans, then perhaps you'll also find one or more
fan headers no longer work.

The hardware monitor, never has enough channels to monitor everything.
There are two 12V rails. There is the 12V_mobo, a single wire on the
main connector. There is the ATX12V 2x2 which powers only the processor.
That could have an abnormally low voltage on it, and the Vcore
regulator could continue to run. Switching regulators can run over
a wide range of voltages, but running them from a low voltage
(like 6 volts), increases the current they draw, and the burning
could actually be something being tortured by the extra current.
A switching regulator tries to maintain the output power level.
In my example above, 12V @ 5.6 amps. If my supply instead delivered
6V to Vcore, it would draw 11.2 amps instead. And those amperes
could burn something. Since the hardware monitor doesn't typically
monitor both 12V supplies to the board, your multimeter may be
needed to verify both of them. Probe the back of the
2x2 ATX12V and the back of the main connector, while the system
is running, and check that both are OK. It is unlikely, that
they're split and separate inside your power supply, so if one
is low, they should both be low. In the power supply, they may start
from a single source, be routed through two separate current limiters,
then go to power the two 12V circuit paths on the motherboard.

When probing voltages on my PC, I plug the black lead, into a
screw on the I/O connectors on the back of the computer. I do
that, to avoid shorting the leads together. Once the black lead
is secure, I can probe the running computer with the red lead
(like poke the exposed metal on the backside of the two power
connectors).

Good luck,
Paul
From: Brian Downing on 16 May 2010 09:54
"Rob" <noone(a)nowhere.noway.com> writes:

> The PC is basically working then (you say you have accessed the BIOS
> and looked at the hardware monitor screen.) Ignore that 12V reading
> from that for now, as your PC wouldn't even get that far if +12V was
> missing.
> I assume then that XP is failing to boot. Any error messages?
> What do you actually see on the screen?

Yeah, XP fails to boot but CPU fan's not spinning. Need an alternate
supply before I let it idle much.

Was looking for actual ASUS Schematic so I could trace from 12V source
along to dead component. None really "appear" toasted.

Thanks for the response

--
bsd(a)panix.com
From: Brian Downing on 16 May 2010 13:02
Brian Downing <bsd(a)panix.com> writes:

> Yeah, XP fails to boot but CPU fan's not spinning. Need an alternate
> supply before I let it idle much.
>
> Was looking for actual ASUS Schematic so I could trace from 12V source
> along to dead component. None really "appear" toasted.

Here's the current error message...

CMOS Settings Wrong
CMOS Settings Data/Time Not Set
Chassis Intruded !
CPU Fan Error !
Fatal Error... System Halted.


These suckers are going for $150 on eBay (all sold with CPU+RAM).
For that I can build a replacement, I just gotta reinstall
years worth of software.


--
bsd(a)panix.com
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