I have a CZ-600C which had issues with failing tests for Text RAM (VRAM) that I repaired. Thought notes might be useful, since I found basically no info about doing this online, so had to research this a bit myself :)
Repair for Graphics VRAM should be exactly the same.
A more indepth writeup with pics is at: https://buffis.com/repair/sharp-x68000-vram-repair/
Some TL;DR takeaways that I could not find info about online:
- IC1-IC16 on graphics sub-board is Text VRAM
- IC17-IC32 on graphics sub-board is Graphics VRAM
- All VRAM chips are MB81461-12 (x68000 has 32 of these)
- Donor VRAM IC's can be found on Mega Drive (2 per unit)
- Figuring out which IC is bad can be done by looking at the bad address range, bit error mask and x68000 schematics. I should probably write something about this up in more depth later.
(https://i.imgur.com/lWbFrGo.jpeg)