[Coco] Looking for MPI circuit diagram

[gene heskett]

On Sunday, December 12, 2010 05:12:48 pm Robert Gault did opine:

> 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?

They are in the link Genes-os9-stf now.  Big hires scans though, and 
complete with some of my own notes, sorry about your dialup Robert.

-- 
Cheers, Gene
"There are four boxes to be used in defense of liberty:
 soap, ballot, jury, and ammo. Please use in that order."
-Ed Howdershelt (Author)
I don't know who my grandfather was; I am much more concerned to know
what his grandson will be.
		-- Abraham Lincoln