I have been working to restore this Portable PC III - apparently made by Origin Systems. All in one 12mhz 286, 1mb ram, and this amber display. Aside from a disassembly and deep cleaning, I’ve done a few repairs so far:

- motherboard caps exploded on first test so recapped the whole board
- dead Dallas RTC chip that was socketed and hacked to take a CR2032
- peripheral I/O card with bad caps
- 3.5” floppy not working, waiting on caps to be delivered to see if that works.

Main problem as seen is the graphical display. This card appears to be a CGA/MDA card. Text displays fine. When I go into any sort of graphical mode there is corruption - bottom half is just garbage and the top half is shifted around. The programs still run in the background.

I ran the checkit video tests and it showed a pile of VRAM problems as shown. I socketed the two LH2464-12 ram chips in U25/31 and replaced them with new chips, but the behavior is exactly the same. I also replaced the two tantalum caps at the bottom of the board.

I switched into MDA mode with the dips but same behavior with Hercules graphics.

This display connects with the two ribbon cables so it’s not like I can easily switch out to a different display card.

Hoping someone can help point into what direction I should go because I’m at a loss. These PC IIIs have very little information out there and absolutely no schematics or information on this video card.

Thanks