Wife's Computer Won't Start -- Any Ideas?

[Ed Medlin]

speaking of switches....i just had one (again) with a stuck switch. I had
to push it quite a few
times before it came loose. System powered right up.

LOL.....just had one of those on a freind's system. I hate problems like
that.....can make you pull your hair out. I wound up plugging in the
power-on lead into the reset switch to find it. It is still working that way
until I get the switch from Lian Li. Personally, I think Jim should go ahead
and get a PSU for his system. At least he can better isolate the problem and
at best fix it.

Ed

 

[jim evans]

More info

I shorted the power-on pins at the PSU>MB connector.

When the PS_ON is shorted to ground the power supply fans start and I
hear something click-on the in the system, but the moment I remove the
short everything stops.

-- jim

 

[Rod Speed]

OK Here's some new data.

With the mainboard power connector disconnected, two
hard drives, a floppy drive and a CD drive connected
the fan comes on and all voltages look normal.

Under load the +12v reads 11.7v (within specs).

Yep, that's fine.

With the power connector plugged in to the MB I checked the
PS_ON pin. It was 5v, and never changed when the power
button on the front of the machine was pushed. I know this
button works, so for some reason closing the power on switch
does not cause the PSU to receive the power on signal/state.

I'd short the pins the power switch connects to on the motherboard,
just to eliminate the possibility that one of the wires has broken
internally. Not common, but it can happen.

If that produces the same result, looks like the motherboard has passed its useby date.

Check for bad caps on the motherboard. These are usually blue or black
plastic covered post like things that stick up vertically from the motherboard.
The tops should be flat. If any have bulged or have leaked, thats the problem.

More info

I shorted the power-on pins at the PSU>MB connector.

When the PS_ON is shorted to ground the power supply
fans start and I hear something click-on the in the system,
but the moment I remove the short everything stops.

More evidence of a motherboard problem if shorting the pins
the power switch connects to doesnt see the PS_ON# line go low.

 

[jim evans]

I'd short the pins the power switch connects to on the motherboard,
just to eliminate the possibility that one of the wires has broken
internally. Not common, but it can happen.

Just did it. Nothing.

If that produces the same result, looks like the motherboard has passed its useby date.

And I probably can't get a replacement since it's been discontinued
for some time.

Check for bad caps on the motherboard. These are usually blue or black
plastic covered post like things that stick up vertically from the motherboard.
The tops should be flat. If any have bulged or have leaked, thats the problem.

Somebody else suggested that and the tops are not bulged and the all
look clean and normal. And, Soho isn't one of the manufacturers
listed as using the bad caps.

More evidence of a motherboard problem if shorting the pins
the power switch connects to doesnt see the PS_ON# line go low.

Looks like the motherboard has left the building. Thanks for all your
help.

Oh yes, one more thing. I bought a power supply tester and the power
supply tests OK.

-- jim

 

[jim evans]

In 25 years of using and maintaining two PC computers this is my first
MB failure. I've had multiple failures of every other component, but
never a motherboard. Oh, well . . . I guess I was due.

-- jim

 

[Rod Speed]

Just did it. Nothing.

And I probably can't get a replacement
since it's been discontinued for some time.

Yeah, tho its worth checking ebay to see if someone has
discarded one when they upgraded to something better.

Somebody else suggested that and the tops are not
bulged and the all look clean and normal. And, Soho
isn't one of the manufacturers listed as using the bad caps.

Looks like the motherboard has left the building.

Yeah, likely a cracked trace or dry joint.

Might be worth checking for that around the 20 pin ATX connector
and the pin used by the PS_ON# green wire, easy to fix if its that.

Thanks for all your help.

Thanks for the feedback on what you tried, too rare in my opinion.

 

[Rod Speed]

In 25 years of using and maintaining two PC computers this is my
first MB failure. I've had multiple failures of every other component,
but never a motherboard. Oh, well . . . I guess I was due.

Yeah, I've only had one myself, and thats a bit surprising
given that they are by far the most complex part of a PC
except arguably the cpu.

 

[johns]

Bad electrolytics. The SOYO had them on the
mobo, but probably, your bad ones are in the
start circuit of the power supply. Leaving it on
like that will fry those cheap capacitors. Replace
the psupply, and if that doesn't work, then the
mobo has them too, and it is history.

johns

 

[johns]

It's the start circuit in the psupply. The
voltages will test OK, but the start circuit
will not let the system power up.

johns

 

[Rod Speed]

It's the start circuit in the psupply.

Nope, the motherboard isnt putting up
PS_ON# when the power switch is pressed.

The voltages will test OK, but the start
circuit will not let the system power up.

Yes, but thats on the motherboard, not in the power supply.

 

[johns]

Yes, but thats on the motherboard, not in the power supply.

I just went throught that with a bunch of Antec supplies.
The start circuit electrolytics had failed, but all the
psupply voltages measured OK. There's no start supply
voltages on the mobo connector to measure, but I could
see the problem when I opened the psupply case ... 2
swollen goopy electrolytics in the starter circuit.
Still, her running that thing all the time could certainly
fry the mobo electrolytics .. like you say.

johns

 

[Rod Speed]

Rod Speed wrote

I just went throught that with a bunch of Antec supplies.
The start circuit electrolytics had failed, but all the
psupply voltages measured OK. There's no start supply
voltages on the mobo connector to measure, but I could
see the problem when I opened the psupply case ... 2
swollen goopy electrolytics in the starter circuit.
Still, her running that thing all the time could certainly
fry the mobo electrolytics .. like you say.

And we know that the motherboard isnt putting
up the PS_ON# line when the power switch is
pressed or when the power switch pins are shorted.