November 7, 2026

MOD_EMUP - power supply

While I am waiting for my circuit boards to arrive, I began thinking about a power supply. We need 5V, 12V, and -12V. How much 5V? We don't know, and it will be something to measure when we are able to hook something up. This will be easy when the boards arrive.

I dug around in my junk and found an ancient PSU from some old PC. No 3.3 volts on this one. It is a "Glitch Master" -- made in USA. It has a 1997 date on a test sticker. 250 watts, with 25A of 5 volts, 9A of 12 volts, and 1/2 A each for -5 and -12. Wire colors: 

Black -- ground
Red   -- 5V
Yellow - +12V
Blue  -  -12V
Orange - ?
White  - ?
Green  - probably power enable
The green wire must be continually connected to ground for the supply to fire up. I need to use two old hard drives as a load to get the supply to run. This old monster needs a pretty hefty load to run right.

I measure 5.4 volts on the 5 volt lines. The white and blue wires touch together by accident and now the supply won't work. Oops.

A second supply

This one has proper connectors on everything, so there should be no accidental touching of wires together. I have a couple of candidates that also supply 3.3 volts. Color markings are even indicated on the sticker: 
Black -- ground
Orange = 3.3 V
Red  = +5V
Yellow = +12V
Blue  =  -12V
White  = -5
Green  - PSU on
Purple = +5 standby
Grey - power good indicator
It runs nicely with an old IDE hard drive as a load. I could continue with that, or use a resistor. I see claims that a 10 ohm resistor might do, but I imagine this depends on the details of the specific power supply. The EMUP itself might be a sufficient load, and likely will be.
Have any comments? Questions? Drop me a line!

Tom's Electronics pages / tom@mmto.org