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IBM BIOS wont start after 640K mod

SpidersWeb

Veteran Member
Joined
Feb 16, 2012
Messages
2,697
Location
New Zealand
I'll just list what's happened with this board:

- Perfectly working 64-256KB motherboard I had as a spare
- RAM and ROM and U84 taken from very bad condition 640KB board
- E2 soldered
- No start, so used Supersoft/Landmark ROM, found bad RAM chips and replaced. A0000 OK, including self-refresh, no abnormal faults.
- Reinsert IBM ROM's, no start
- Reinsert IBM ROM's it was using before mod, no start

The IBM ROMs from the damaged XT are definitely goneburgers.
But the ROMs that were in it before were checked, and rewritten - I tried both the May 1986 BIOS and the 1982 BIOS. It isn't having it.

- Installed DTK ERSO BIOS ROM (2764) - machine starts but complains about KB error even when KB is connected and keyboard doesn't respond - so perhaps another job? Not sure if DTK might've accessed the keyboard differently or it's broken.
- Installed Supersoft/LandMark ROM again - says everything is golden (also an 8K image though)

Any ideas?
 

Chuck(G)

25k Member
Joined
Jan 11, 2007
Messages
39,810
Location
Pacific Northwest, USA
Probably not the keyboard BIOS. On XT-class machines, the keyboard interface is very simple--basically a shift register, so I'd start by checking signals there.
 
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