[clug] Any ideas on what to look for to get an old PC running?

David Tulloh david at tulloh.id.au
Wed Dec 31 15:35:27 GMT 2008

jhock wrote:
> Hi All,
> Today I got a chance to pull apart the PC.  I disconnected everything
> and tried to start it by jumping the power switch pins.  Still no luck.
> Nothing happened.  (By the way.  This computer worked well before it was
> put into storage.) 
> I then connected the power switch and initially the fans came on.  I
> then couldn't switch off the power using the power switch. I switched
> the power off at the wall. After connecting the power again I couldn't
> reproduce the fans on using the power switch.  I tried jumping the power
> switch pins but I still couldn't get anything to work. Maybe the power
> switch is faulty.
I've noticed this, what it looks like to me is that the fan settles into 
a set spot.  I'm not sure what exactly is going on power wise but it 
always seemed to settle into a few consistent spots for me.  So once it 
settles once it probably won't do it again unless you move the fans 
> ... I then found my old analogue multi-meter and started looking at the
> volts coming from the power supply. ...
>       |orange|red|white|yellow|blue|purple|black |green |grey |
>       |+3.3v |+5v|-5v  |+12v  |-12v|+5v SB|com   |PS-on |P.G. |
>       |      |   |     |      |    |      |return|remote|PW-OK|
> black |-     |-  |-    |-     |-   |5v    |      |1v    |1v   |

Did you switch on the power supply before doing this?
The ATX molex connector includes an on switch, this needs to be shorted 
to ground (permanently, not just touched) for the power supply to work.  
This is the green wire you identified, pin 14.  In the past I have used 
a bent stapler and shorted it into one of the adjacent grounds.

When the device is not switched on the only active power rail is the 
+5VSB, the purple wire.  So your above results would be exactly as expected.


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