11 Dec
2010
11 Dec
'10
2:16 p.m.
Now, you mention that the ROM version is not what you'd expect. I assuem
this ROM versions is displayed on the CRT -- that is it somehow involves
reading the ROM. If the ROM was corrupted, then it moight report the
wrong version.
Yes, that did cross my mind too Tony. But the serial number on the ROM
doesn't correspond exactly to the serial number I've seen on the web for an
H/88 ROM chip so ...who knows. It's certainly a possibility though.
Using your logic probe, check the address and
(especially) the data lines
on that. Are any stuck high or low?
Well, A9 does seem to be at a steady voltage of about 4V whereas all the
other address lines are a wave. This is suspicious. I'll measure it again
just to make sure.
Is there any way you can get a dump of a known-good
disk cotroller ROM?
If so, eitehr burn it into an EPROM and replace your firmware ROM, or
compare it with a dump of your ROM.
Not currently. There may be a ROM dump out there someone. I haven't looked
hard yet. I have bought an EPROM burner but haven't used it yet. It might
allow me to compare or at least view the code. Bear in mind this is still a
steep learning curve for me. I'm not sure these modern EPROM burners can
read or burn the equivalent of old ROMS like this without some hardware mods
along with it, but I can investigate.
It seems that most of the evidence so far, does point to the ROM, although
not exclusively.
Terry