Thanks! RE:XT Diagnostic ROM and POSTcard

Andrew Lynch lynchaj at
Sat May 31 08:18:31 CDT 2008

Hi All,

I just wanted to say "Thank you" to everyone who helped me fix this classic
IBM XT motherboard with the Diagnostic ROM image and the settings for the

Long story short, I replaced a 74LS245 and a faulty DRAM chip and now the
board boots fine.  

Of course half the fun is finding what actually works, what doesn't, what
appears to be broken but actually works, what is broken but appears to be
working, etc.  You know the drill, I am sure.

Fixing an old broken 16 bit VGA card which works in an 8 bit ISA slot helped
a lot.  As did the old style PC/XT style floppy drive controller...

So anyway, it's fixed and I booted MS-DOS 5.0 and the Advanced IBM
Diagnostics from a 5.25" floppy disk drive.  So I think we are there.


Andrew Lynch

PS, BTW the XT Diagnostic ROM image seems to work best when burned into a
2764 EPROM.  I tried various other types of EPROM but the 2764 seems to work
best.  I think IBM did some weird remapping of their custom Mask BIOS ROM...

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