Dead motherboard?

[Guest]

Hi,

I've got a friends pc that is not doing anything at all. It's about 3 years
old, has a P4 Gigabyte 8S651MP-RZ motherboard with P4 CPU.

I unplugged everything and check that there was power coming in. Everything
looks fine, all fans turning and the mobo light comes on. I plugged the HDD
back in and I can hear it starting up. I did check the HDD on another system
and did a diagnostic on it, everything checked out 100% ok.

There is no BIOS loading and no warning beeps of any sort. Reset bios.
Checked battery. Checked all components for connection and seating.

Have swapped monitors to one I know works.

Completely and utterly DEAD. The deadest computer I have seen.

Would I be correct in assuming the motherboard has had it?

 

[Bob Harris]

Another possibility is that the portion of the power supply connecting to
the motherboard is bad/loose, but the portion running the hard drive is OK.
This would be rare.

If the CPU were dead, I am not sure what one would get. I assume at least
some beep code?

So, odds are the motherboard is dead.

 

[w_tom]

...
I unplugged everything and check that there was power coming in. Everything
looks fine, all fans turning and the mobo light comes on. I plugged the HDD
back in and I can hear it starting up. I did check the HDD on another system
and did a diagnostic on it, everything checked out 100% ok.

There is no BIOS loading and no warning beeps of any sort. Reset bios.
Checked battery. Checked all components for connection and seating.
...
Would I be correct in assuming the motherboard has had it?

Not until you have first done even simple first data collection.
Currently I see no numbers. Therefore no one has any idea what is and
is not working. It's called wild speculation. Let's terminate the
speculation now and move on to find the problem.

Verify integrity of each component - then move on to other
suspects. Currently you don't even know if the system has power.
Even if a fan turns, still, system may have no power. Get a 3.5 digit
multimeter for about $20. Start with a computer's foundation - the
power supply 'system'. Notice I did not say power supply. Procedure
to confirm integrity in only two minutes is "When your computer dies
without warning....." starting 6 Feb 2007 in the newsgroup
alt.windows-xp at:
http://tinyurl.com/yvf9vh

Is battery on motherboard good? Again, do not remove or change
anything. Measure that battery with a multimeter. 3 volt battery
must measure above 2.8 volts. A startup failure might only occur is
battery is well below 2.4 volts. If battery is at 2.8, then battery
is ready for replacement but not a reason for failure.

Post numbers here. Those numbers may identify a suspect or may also
provide other useful information - facts in those numbers that is not
apparent to you. Without those numbers, then every reply will only be
wild speculation. Get the meter. Follow the evidence (as said
repeatedly in CSI). Only then will useful answers be obtained.

 

[Guest]

Hi w tom,

Here are the readings that I have just taken..

Purple to motherboard - 4.95v
Green - off 1.1v on 0.13v
Grey - 0.95v
Orange - 3.31v
Red - 5.07v
Yellow - 11.84v

 

[Guest]

Hi w tom,

Here are the readings that I have just taken..

PURPLE to Motherboard - 4.95v
GREEN - 1.1v off / 0.13v on
GREY - 0.95v
ORANGE - 3.31v
RED - 5.07v
YELLOW - 11.84v

Regards,

Kevin

 

[Guest]

Hi w tom,

Here are the readings that I have just taken..

PURPLE to Motherboard - 4.95v
GREEN - 1.1v off / 0.13v on
GREY - 0.95v
ORANGE - 3.31v
RED - 5.07v
YELLOW - 11.84v

Regards,

Kevin

 

[Guest]

oops.... sorry about the triple post.
I kept getting a 404 error and went back to repost. Didn't know it would go
through anyway.

 

[Guest]

oh..

And the CMOS battery is 2.92v

Kevin

Hi w tom,

Here are the readings that I have just taken..

Purple to motherboard - 4.95v
Green - off 1.1v on 0.13v
Grey - 0.95v
Orange - 3.31v
Red - 5.07v
Yellow - 11.84v

 

[w_tom]

Hi w tom,

Here are the readings that I have just taken..

PURPLE to Motherboard - 4.95v
GREEN - 1.1v off / 0.13v on
GREY - 0.95v
ORANGE - 3.31v
RED - 5.07v
YELLOW - 11.84v

Green wire voltage is too low when powered off. But power supply is
turning off anyway.

However grey wire voltage never tells motherboard that voltage is
OK. Computer will not start until that voltage well exceeds 2.4
volts. There is the problem in the power supply 'system'.

Now why is that signal remaining defective? Other voltages on
orange, red, and yellow wires are OK. Therefore either the voltage
monitor inside power supply is defective OR something is shorted on
that same signal wire on motherboard.

Now we separate the two suspects. Disconnect the power cable (or
course all changes must be made with AC power cord removed from wall
receptacle). Use a paper clip to connect green wire to any black
wire. When power cord is installed, hopefully, those orange, red, and
yellow voltages will return. We cannot say with certainly because
some supplies will not startup without a load. However if those
voltages do meet spec, then measure voltage from grey wire (to any
black wire). Does that increase to well above 2.4 volts? If yes,
then set the meter to current mode setting to measure up to 2 amps.
Slowly decrease the current range until current from grey to black
wire is measured. That current must be above 0.02 amps (20
milliamps).

If the grey wire outputs sufficient voltage and sufficient current,
then failure is on motherboard. If that grey wire voltage or current
is not sufficient, then the voltage monitor circuit inside an
otherwise perfectly good power supply has failed (or was always
defective from factory).

If that problem is on motherboard, you can use the meter (in
continuity mode) to trace where PC traces from that grey wires to
associated IC on motherboard. You are looking for something shorted
from that trace to other traces. The problem could even be a wire
short embedded beneath the green solder mask material - so small as to
require an eyelet magnifying lens. However if nothing can account for
the short, then the problem would be inside related integrated
circuits - complete motherboard replacement required.

Is this failure due to surges? Well many somehow know. This failure
is typical of how most things fail - simple pre-mature component
failure probably due to a manufacturing defect.

Finally, once the power supply or motherboard is replaced or
repaired, then use the meter to confirm system is working BECAUSE that
voltage is now correct. Notice what that voltage was: 0.95. It's
neither too high nor too low. It must be well below 0.7 or it must be
well above 2.4. IOW system could work today and fail tomorrow.
Always confirm the repair also fixed the problem. When solved, that
grey wire voltage will never sit between 0.7 and 2.4 volts.

Bottom line: known is what failed, what to do to fix it, AND what to
look for to confirm it is repaired.

 

[Guest]

Hi w tom,

firstly, many thanks for your assistance and expertise with this problem.
Much appreciated.

I checked the orange red and yellow voltages after using a paper clip to
connect gree/black.
Voltages were the just about the same as before..

Orange - 3.31v
Red - 5.07v
Yellow - 11.82v

However, when I checked the grey/black connection I didn't get any voltage
at all.

Just to check if I was doing it correctly, I connected a paper clip to the
grey/black and checked the voltage going through the paper clip which came up
as 0. This was with th pc OFF and ON.

Can I assume from this that it is the power supply?

Regards,

Kevin

 

[Guest]

EDIT TO LAST POST

Tried checking grey/black again.
Used Black probe to Case and Red probe to Grey wire. Result 0.97v
Black probe to Black wire and Red probe to Grey wire. Result as above.

Power supply then?

 

[w_tom]

EDIT TO LAST POST
Tried checking grey/black again.
Used Black probe to Case and Red probe to Grey wire. Result 0.97v
Black probe to Black wire and Red probe to Grey wire. Result as above.

Power supply then?

Apparently power supply voltage monitor has failed. Also currents
listed for each voltage on the original supply should be sufficient
for that system; numbers to select a new supply.

Failure is most likely do to an internal failure of some component -
not due to external events.

Of course, when a new supply is installed, one measurement to
confirm the problem has been solved: voltage on that grey wire. Once
the system has booted, have it access all peripherals simultaneously
(multitask) and then measure voltages on red, orange, yellow, and
purple wires. This confirms a new supply can supply the load and is
working with sufficient margins. Some supplies can work fine in a
computer, yet have a low voltage under max load, and then fail months
later. Meter will then confirm in but minutes that supply really is
as strong as its numbers claim.

 

[Guest]

w_tom

Many thanks for your help, much appreciated.
You have taught me something new.

Regards,

Kevin

 

[Guest]

Could have sworn I posted the end result here before??

Anyway, this problem turned out to be the CPU and not the power supply.
Just thought I'd let you know. (Again)