CD32 PSU replacement

How to use a PC PSU with an Amiga CD32.

 

PC Power Supplies as replacements/upgrades

It is quite common now to replace the under rated original Amiga PSU with a PC one, asPC PSUs start at 135W and go to over 500W it is easy to see why.

There are minor differences in using an AT or ATX PSU to power an Amiga and leter on I will explain the witing.

AT PSU

Not really used in PCs since 1998/99 due to the PC requirement that software can switch
the PC off (or a Microsoft plan to stop their software crashing).

Normally found in old/dead PCs (they have some uses). To hook it upto your Amiga you will need to note wiring of the square DIN plug (check the underside of the PSU) and then cut it off.

Commodore never seemed to use the same colour code in all Amiga models so you will need to check your wiring with a multimeter. See the power connector section for more details.

Once you have wired up the Amiga cable, connect a 21W car bulb across the +5V (RED) and 0V (BLACK) wires. This will provide a suitable load to turn on the PSU and you can then ensure you have the right voltages going to the right pins before pluging into your Amiga.

If all seems well, connect to your Amiga and switch on!

Important note. Modern PSUs have what is called crow bar protection, if you short it out or wire up backward, to cause a large power surge, it will switch off. Don't count on this, double check your wiring!

Some AT PSUs had the mains switch inside the PSU housing, that is fine. Some had a mains lead that went to the power switch on the front of the PC case. If possible avoid this type unless your Amiga case has a suitable power switch.

Final note, do not open a PSU case. Due to their operation, a typical computer power supply can have upto 400V DC stored within for a considerable time after power off. If you inadvertantly touched the wrong part you could be killed!

ATX PSU

This is the type of PSU found on all modern PCs and within cases. There are 2 important differences to the AT PSU. The following conditions must be met.

1) You need to have about a 1.0 Amp load on the 5V supply for it to work.
2) You need to connect the PS-ON line to ground for the PSU to switch on.

Condition 1 is easily satisfied, an Amiga uses enough current on the 5V supply.

Condition 2 is a bit trickier.

It is possible to create a simple circuit to use the push to make power button of
an ATX case. A simpler solution is to bare back the insulation of the PS-ON wire
(normally green) and of a ground wire (black). Then either twist them together or
add a link wire, solder it an insulate it. Now when you use the mains switch on
the back of the ATX PSU, it will switch on the PSU.

the circuit to utilise the PC front panel switch is available here

Updated 08 July 2017