Upgrade iMac G3 computer with a Mac Mini M4

I upgraded my iMac G3 by swapping the old computer for a Mac Mini M4.

This process is summarised and shared in my YouTube video

This repository is incomplete.

• If you're planning on building this yourself, you probably want my PCBWay Order Files

I intend to fully document my process as a post on my patreon (free to follow), and to upload all the files needed to this repository.

Until then, here's a quick brain-dump of some hurdles I had to overcome.

Full Disclosure: my YouTube video was sponsored by PCBWay, and they provided their services for free.

Printed Circuit Boards

This was entirely possible thanks to @qbancoffee's PCB design work. I forked the repo, graffitti'd the boards, and got them produced and assembled by PCBWay.

Boards used

• imac_g3_333mhz_slot_loading_J20_adapter_board (surface mount version)
• imac_g3_down_converter_board_adapter
• imac_g3_slot_loading_J22_adapter_board

Bills of Materials

• Final BOMs available in the Matt's PCBWay Order folder.

Assembly Issues

I ended up with two issues with the J20 Board that I didnt spot until PCBWay encountered them during assembly:

1. The VGA connector J4 didnt match the footprint well enough for PCBWay to solder it in.
   • I got them to leave it disconnected, and post it to me with the otherwise-assembled board. I was able to bend it slightly to fit and it works fine.
2. I accidentally specified a shrouded header for J3, which clashed with capacitor C10.
   • They assembled it with it floated above, but I also specified the wrong orientation for the header's key. So I ended up cutting it off.
   • I have swapped them out for non-shrouded headers in the Matt's PCBWay Order BOM.

Programming the Microcontroller

I ended up using a USB Tiny ISP programmer and the command line rather than the Arduino IDE to flash the microcontroller.

I ended up modifying the arduino code to work round some issues I came across.

Microcontroller Issues

• (IIRC) I could not get the USB interface to work.
• I could not get it to output an EDID
• It didn't detect the vsync, therefore kept turning the screen off, so I removed that timeout from the code
• I updated the serial interface for tweaking the screen parameters to make more sense to me.

3D Printed Mac Mini Frame

I 3D printed a frame to mount the Mac Mini in the HDD/CD holder.

Ideally the mac mini would sit slightly further forward (maybe 5mm?) because the dimples on the metal shielding try to occupy the same space as the back corners.