[Coco] More MPI mischief...

[Brian Blake]

Okay guys, got another MPI mostly works problem. I picked up a couple of
MPI's recently - 3124 variety and I do not believe there is an 'A' behind
them (at work so I can't tell).

Config: 512k CoCo3, FD-501

So far, I haven't found any s/w that will not load via disk (except certain
OS-9 due to it not being PAL upgraded) thru the MPI.

While the MPI seems to function normally, most of the time, I have found an
issue with it. Keeping in mind I have not taken the cover off to do any
measurements, I can say that I have entered the requisite POKES & PEEKS and
all of those came back as would be expected.
The problem occurs when I am trying to use the O-90 pak. Either from booting
to the pack or by POKEing in the appropriate slot, I get no audio from the
pack. As a matter of fact, just using the sample file in the O-90, I press
'S' to score and then 'P' to play, I don't even think the song actually
plays at all. The 'P' will hang around on the screen until I hit the 'BREAK'
key (waited 5 minutes one time last night, the song is about a minute long).
I have 2 other MPI's that the O-90 works in (verified that last night), and
it plays properly when plugged directly into the CoCo expansion slot.

Looking at the schematics for the O-90 and the MPI, SND (slot connector pin
35) is unbuffered from the CoCo to the MPI slots (all slots should have the
same signal on pin 35, regardless of what is plugged in or selected).


>From my under-educated point of view, it appears to me that I am looking at
only a few possibilities possibilities: Broken trace on the MPI (would that
prevent the music from actually starting)? Weak power supply in the MPI
(doesn't makes sense if the FD-501 works fine)? Piece of debris shorting
pins 33/34 to pin 35? (I would assume grounding out pin 35 would kill all
sound from the CoCo, this does not happen as I can play games loaded via the
MPI and still have sound).

Any other thoughts or suggestions?