11 Dec
2010
11 Dec
'10
1:29 p.m.
Ok, an examination of the comments in the ROM H listing suggests that the
Lisa 2/10 does look to see if the hard drive is connected and if not, then
boots from the floppy drive. As the machine still gives an error number 57
on the I/O board when the widget is unplugged but the floppy drive plugged
in, I deduce the fault is definitely is on the main I/O board somewhere.
With the widget unplugged then I took some readings on the floppy drive card
edge and compared those to the same on the working Lisa. There were some
differences. Compared to the working machine..
PH0 does not show a brief 5V pulse on start up
PH1 and PH2 remain at zero rather than pulsing briefly to 3.5 v or so every
4-5 seconds
HDS is static at zero rather than at 4.5v and dropping to zero every 4-5
seconds
DEN (ENBL) is 5v rather than zero
WRD is 5v rather than zero
PWM is 0 rather than 4v
In other words the drive probably isn't being electroncially accessed
(r.g. to check if there's a disk inserted).
Now, from what another poster was saying, one of the errors you got means
that the 6800 can't access the disk cotnroller RAM (shared with the
6504). I wonder if that 6504 is hackign up for some reason. Either
because it's waiting for an I/O device to do something (which could mean
a fault in the IWM chip), or becuase it's firmware is corrupted and thus
the 6504 is going crazy.
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.
Using your logic probe, check the address and (especially) the data lines
on that. Are any stuck high or low?
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.
-tony