Re: Dead motherboard?
- From: "w_tom" <w_tom1@xxxxxxx>
- Date: 13 Mar 2007 16:23:53 -0700
On Mar 13, 8:16 am, kleefarr <kleef...@xxxxxxxxxxxxxxxxxxxxxxxxx>
wrote:
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.
.
- Follow-Ups:
- Re: Dead motherboard?
- From: kleefarr
- Re: Dead motherboard?
- References:
- Re: Dead motherboard?
- From: w_tom
- Re: Dead motherboard?
- Prev by Date: Re: diskette drive seek error
- Next by Date: Re: System notifications are not appearing anymore!!!!!!!!!
- Previous by thread: Re: Dead motherboard?
- Next by thread: Re: Dead motherboard?
- Index(es):
Relevant Pages
|
