apple Lisa2. One working!! - one to go?

[Tony Duell]

> 
> 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