If you dabble with old computers, then you know the power supplies can fail just as often as the computers themselves. In the case of classic Macintosh computers, Apple didn’t use any kind of standard PSU, so buying new replacements isn’t possible. When a classic Mac PSU fails, the options are to recap and rebuild it, or make an adapter for another type of power supply. PC-style ATX supplies are cheap and readily available, and they offer the same +12V, +5V, -12V, and standby power outputs as Mac supplies. Wouldn’t an ATX-to-Mac PSU adapter be nice?
George Rudolf designed this simple ATX adapter and shared it on GitHub. It coverts a standard ATX 20-pin connector to the 10-pin connector found in the Macintosh IIcx, IIci, IIsi, IIvx, IIvi, Performa 600, Centris/Quadra 650, Quadra 800, and PowerMac 7100.
Aside from the different connectors, there’s also one small bit of active electronics on the adapter: an inverter for the ON signal. Classic Macs and PCs both support soft power, where the computer can be turned on from the keyboard or via software instead of with a hard on/off switch. This requires a power supply enable signal from a circuit using standby power, but the polarity of the ATX enable signal is the opposite of the Mac. Inverter to the rescue.
I was able to get 20 adapters assembled and shipped from JLCPCB for the princely sum of just $1.39 each. The connectors had to be sourced separately, but they’re readily available. Soldering the connectors only takes a few minutes, and they’re easy through-hole components.
I put together one of the 20 kits and installed it in my Macintosh IIci, and it worked great. I think it’s more useful for bench testing purposes than as a full PSU replacement, unless you want to go the extra mile of fashioning custom brackets to secure the ATX PSU inside the case.
For people who are attending Mactoberfest Meetup on October 14, I’ll have nineteen more of these ATX-to-Mac kits as free give-away items. You can assemble the kit right there at the meetup’s repair/work center. One of the Mactoberfest computer demos will also be a Mac IIci powered by an external ATX PSU, so you can see this adapter in action. I hope you enjoy these!
