Rebuilding Apple II Power Supplies

So a friend requested I rebuild two Apple II power supplies for him. They’d both been “worked on” before, so rather than attempting to repair the existing boards, I decided to replace both boards with a modern PSU.

Of the original PSUs, one was a clone and one was an original. The original was already in pieces when I got to it, with components desoldered. The clone was very similar to the original Apple PSU, but cheaper and flimsier. Also one of the previous owners had “hacked” on it, adding an external fan and an additional power switch.

Deciding that I really didn’t want to try and fix 40+ year old PSUs that were already in a state of disassembly, I decided the best course of action would be to replace them with something modern. The original owner liked this and agreed to my plan.

I’ve had a good experience using Mean Well PSUs so I ordered a pair of suitable units from Mouser, choosing the RPT60B based on its voltages and available amps.

These have one minor disadvantage, insomuch as the don’t do -5v, but looking at the -12v rail, versus the rating the Apple II needed, I had plenty of overhead to use a 7905 to regulate some of the -12v rail up to -5v.

The switches on both units needed replacing so I had to widen the opening on the Apple II case ever so slightly, as I couldn’t find a suitable switch in the right size. This was a quick job with a nibbler and a file.

I cut a sheet of acrylic sheet to act as an intermediatary layer between the original mounting posts and my new components. I used insulated crimps where possible and a screwdown terminal block to make construction easier. 

Finally I ran up a small 7905 daughter board, complete with isolated heatsink to handle the -5v rail. This consisted of two capacitors, the 7905 and a small piece of veroboard.

Assembly went smoothly and I’m really happy with the results. I also have the remains of the original Apple II PSU in case someone local needs to repair one.






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