Peter Shoebridge wrote:

> I know this has been up here before but....

  It has.

> There is a way to fool a PC power supply to work without plugging it
> into a motherboard. If I remember, it involves shorting two wires,
> it's just which two.

  No, shorting wires is the way to "fool" it into not working, maybe
ever!  Put a 10 ohm 5 Watt (Wirewound) resistor across the +5V output
(between red and black wires) to give it a load.  Such a light load will
cause the +12V supply to run slightly under-voltage but this usually
does not matter.  An easy load is a discarded/ antique 5" floppy drive.
Personally, much of the time I just grab an old AT motherboard with
Ni-Cad disease (also called cancer).

  I have been meaning to "get professional" and build a dummy load.
Start with a dud motherboard as mentioned, remove the firecracker bypass
capacitors and other components within 1" to 2" radius of the power
connector and hacksaw this piece of the motherboard loose.  File the
edges smooth to avoid protruding "hot" traces, find "dead" areas (no
power traces) and drill holes to mount to a wooden (bakelite if you have
it) base with spacers.  Identify power traces as required and scrape the
green off (or just solder to the underside of the connector - not as
neat), and tin these.

  Get a jug element complete with ceramic former, calculate resistance
per turn and total.  For example (US), 1000W at 110 volts is 9 Amps,
must be about 12 ohms.  Half of this is 6 ohms, will draw 2A from the
+12V supply (24 Watts).  Other half is of course 6 ohms too, if divided
by 5 will be 1.2 ohms and will draw four amps from the 5V supply (20
watts).  I'll take a punt and guess that the jug element has ten turns
of spiral wire.  Otherwise, just recalculate.

  Mount it by standoffs to the baseboard, and on the same side as the
end connections, carefully pull out taps at 1, 3 and 5 big turns (i.e.,
of the former).  Straighten the taps out for 7mm or so so that they make
a neat flattened "U" of wire and run smoothly back into the spiral.
Connect them using crimp ferrules to your TCW links, linking turn 3 to
the +5V point, 1 and 5 to ground, and 10 to +12V.  The "zero" turn end
is not used; you could have used it and turn 4 for ground with 2 to +5V,
but 6 ohms and 2A sounded good for the 12V.

  The element will get hot, but not red hot; a guard is recommended.

  You may care to add loads for -12V (a 22 ohm 10W wirewound, or a 33
ohm 5W one) and -5V (10 ohm 5W) though the latter is no longer used.

  A LED on the "Power Good" line would be a nice touch, indeed LEDs on
the four supply lines.  If you tap these to the 2V point (figure it!) on
each load, and use 120 ohm series resistors, they should be quite
sensitive to the voltage.  Even better, tap them to 5V and use a 3V
(3.3V shuld work) zener as well as the 120 ohm resistor and they should
be even more sensitive to the correct voltage.

  Well, that was my imagined dummy load anyway.  I assume we WERE
talking about smoke testing here?

  Cheers,
        Paul B.