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

jhock jhock at iinet.net.au
Wed Dec 31 09:58:35 GMT 2008

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 did notice that when everything was disconnected and as I was pushing
the main power plug (about 20 pins) into the mother board the fans would
come on and off erratically. It seemed to be happening because of the
slight on/off connections when jiggling the plug but still nothing
happened when the plug was fully pushed into the mother board. 

I then found my old analogue multi-meter and started looking at the
volts coming from the power supply.  The fuse in the power supply looks
fine.  It has zero resistance with the multi-meter.  I didn't remove it
because it has been soldered onto the board. The zero resistance may be
through the other side of the connections but I thought that this end
would have shown some resistance.  Hence I assume that the fuse was
producing the zero resistance.  I didn't bother to pull apart the
circuit board in the power supply.

I now suspect that there is something fishy with the power supply.  It
has a chart on the outside showing the voltages of each of the coloured
wires and their rough identity.  I then went through the different
combinations of these to see if they match what is in the chart. There
are some discrepancies as follows.  (I hope the basic formatting works
at your end):

      |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|
orange|      |-  |-    |-     |-   |5v    |-     |1v    |-    |
red   |-     |   |-    |-     |-   |5v    |-     |1v    |-    |
white |-     |-  |-    |-     |-   |5v    |-     |4v    |-    |
yellow|-     |-  |-    |      |-   |5v    |-     |1v    |-    |
blue  |-     |-  |-    |-     |    |5v    |-     |1.5v  |-    |
purple|5v    |5v |5v   |5v    |5v  |      |5v    |-     |5v   |
black |-     |-  |-    |-     |-   |5v    |      |1v    |1v   |
green |1v    |1v |4v   |1v    |1.5v|-     |1v    |      |1.5  |
grey  |-     |-  |-    |-     |-   |5v    |1v    |1.5v  |     |

The first row is the colour of the wire.
The second row is what was written in the chart for that wire.
The third line was also written on the chart.
The other lines are the measured voltages (if any) when the coloured
wire on the left column was connected to the colour in the top row.  Eg.
orange with purple returned 5v.
There were some amps in the chart for different power sources but I only
noted the 250 volt row and only measured the voltages.
The black had "return" in each row.
The green had "remote" in each row except the first.
The grey had "PW-OK" in each row except the first.  I thought  this
might be helpful.

I don't have much to add except that:
      * the voltages don't seem to match what was written on the chart.
        Hence, my suspicion of the power supply.
      * the fans worked when white and green, blue and green, grey and
        green were connected.
      * the fans pulsed on and off when orange and green, red and green
        were connected.

I don't expect anyone to put much time into this.  Today I saw an Eee PC
10 with HDD at JB Hi Fi for about $750.  I think that I will buy that,
format the disk to get rid of M$ XP and load UBUNTU from memory stick.
I hope that works.

Thanks to all for your suggestions.  I really felt like I had some good
leads to work on.


On Sat, 2008-12-27 at 19:48 +1100, Sam Couter wrote:
> jhock <jhock at iinet.net.au> wrote:
> > I was wondering if anybody has any advice on how to get it to work. EG.
> > is there likely to be a fuse inside
> So it's been nearly a week (I've been away), but I never saw this
> particular question answered: Yes, the power supply has an internal
> fuse. They blow sometimes, rendering the entire machine dead. If you
> know which end of the multimeter probes go on the suspect bits it's not
> hard to work out if it's still good.
> Don't touch metal bits inside the PSU with either fingers or metallic
> tools. Some of the big capacitors can bite pretty hard a long time after
> it has been unplugged.

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