u/hedwig_the_great

I’ve been designing a modern internal power adapter for the IBM PCjr called VoltBus.

The idea started as a way to replace aging original power hardware with something cleaner, quieter, and easier to maintain while still respecting the original system and aesthetics. All the connectors and switch were sourced off of the original power supply, with the exception of the 24 pin ATX.

Interestingly, the original inspiration for using a PicoPSU-style setup actually came from an old forum post I ran across years ago. Unfortunately I can’t remember which forum or who originally posted it, but the concept stuck with me and eventually evolved into this project.

Current Rev A features:

- PicoPSU support

- original PCjr rear switch support

- internal mounting

- LP4 power output

- Black PCB with white silkscreen

One thing I wanted to avoid was turning the PCjr into a giant modernized Frankenstein build. The goal is more of a clean “what if IBM had revised the power system later in the product life cycle” type of feel.

I also ran into an interesting issue during testing where some PicoPSU clones don’t properly route PS_ON from the external green wire lead. Genuine units seem fine, but I added a documented fallback jumper method using ATX pin 16 directly so builders can still use clone boards reliably.

I've already got a list of revisions for Rev B like adding a large cutout for wiring so the pico can lay flat with a 90 ATX connector and adding internal trace from the switch to PS_ON.

Right now this project is focused specifically on the power adapter itself, but I’ve been experimenting with ideas for modular add-on boards and stackable internal expansion/power distribution concepts for future revisions and other retro systems.

Still very much an evolving project, but I finally have working prototypes installed and running consistently inside a PCjr. Interested to hear thoughts from other PCjr owners or anyone doing modern internal power conversions on vintage hardware.