[Coco] Looking for MPI circuit diagram

[Robert Gault]

I just had a bug develop with my 26-3024 MPI which has been upgraded for Coco3 
use. I'm thinking I may have a partially blown address chip[ for slot 3 because 
of the following symptoms.

System is a 512K RAM Coco3 with two scsi hard drives, KenTon interface and SC-II 
floppy controller. The hard drive system is set to boot into NitrOS-9 without 
using any floppies.
There are many combinations of SC-II, RS-232 pak, and KenTon interface regards 
slot positions in the MPI. Most of these combinations work perfectly and will 
boot into NitrOS-9 from the hard drive.
One set of combinations will not boot into NitrOS-9 and these have one thing in 
common, the SC-II controller is in slot-3. The boot process freezes just before 
the Welcome message is written to the screen.

I don't see how there can be anything wrong with the SC-II, RS-232, or KenTon 
paks. There is nothing wrong with the software either because NitrOS-9 will boot 
given certain MPI slot combinations. There is nothing in the NitrOS-9 code that 
is slot dependent during the boot process. If there were, note that having the 
SC-II in slot-3 worked in the past as recently as last night.

If an IC in the MPI has blown, which one could produce symptoms of this type 
which seems weird to me. Unfortunately the only socketed IC in the MPI is the 
PAL chip so repairs will not be easy.
A circuit diagram of the MPI might help with this problem. Anyone know where I 
could download a schematic?