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trouble booting

 
 
Neil Green
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      12-24-2006

"Jeff" <(E-Mail Removed)> wrote in message
news:(E-Mail Removed) ups.com...
> i'm not convinced that my motherboard is bad. is
> there a concrete way
> to single out the mobo and make sure it is indeed
> the problem? maybe
> some kind of jumper fell out or something really
> simple like that?


You haven't said what sort of CPU you're running, but
later boards have few jumpers, and jumpers are highly
unlikely to dislodge by themselves in any case.
If you want to be thorough take the board out of the
case to eliminate the possibility of a short to earth
and run the board on the bench on it's own with only
the PC speaker connected using a known good PSU.
You should at the very least get a series of error
beeps through the speaker.
If not then it's a fair bet that either the board or
CPU is faulty.
If you do then add components one at a time until you
can isolate the cause of the problem.


 
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w_tom
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      12-24-2006
Jeff wrote:
> i'm not convinced that my motherboard is bad. is there a concrete way
> to single out the mobo and make sure it is indeed the problem? maybe
> some kind of jumper fell out or something really simple like that?


Yes, and it requires the simple 3.5 digit multimeter. All that
swapping and moving could have been avoided by doing this the first
time.

First, voltage on the purple wire (from power supply to motherboard)
must be measured when computer is off but AC power cord is connected.
That voltage must measure more than 4.87.

Next measure green wire voltage both before and when power switch is
pressed. That voltage must be above 2 volts and then drop to less than
0.8 volts when switch is pressed.

Finally, measure gray wire voltage. It must start at near 0 volts
and then rise well above 2.4 volts within seconds of pressing the power
switch.

Inputs to the to power supply controller are power switch, purple
wire, and gray wire. For startup, the purple wire and power switch
inputs must be correct and of sufficient voltage. If those inputs are
correct and the green wire does not drop below 0.8 volts (order the
power supply on), then either the motherboard controller is defective
(most likely for these defective readings), or power supply has somehow
connected too much power to the green wire (very unlikely but also can
be tested with the meter).

In put a minute with the meter, we would have established where the
problem exists and without swapping anything. I suspect you will find
the green wire voltage does not drop in response to good inputs from
purple and power switch wires.

Check that CMOS battery also with the meter. That 3 volt battery
required replacement if voltage is below 2.8 volts. A voltage of below
2.4 volts would cause problems. But again, second with the meter tells
all - without swapping parts.

 
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