[Coco] MPI problem or ...???

[Mark Marlette]

There is also a large electrolytic cap that after 10-20 years might be  
a bit dry.......

Mark
Cloud-9

Quoting Robert Gault <robert.gault at worldnet.att.net>:

> Brian Blake wrote:
>
>> Greetings all. I ran into a problem with my MPI this weekend.
>> <snip>
>> Then, I tried another 512k CoCo 3. First, with just the FD-502 and
>> everything works fine. Next, the MPI and FD-502 in slot 4, everything
>> worked. Then the SS/C in slot 3, everything works fine. Next up was
>> with the O-90 in slot 2. Not fine... I noticed immediately that it was
>> booting to DECB 1.1 instead of 2.1. ><snip>
>
>  This type of problem looks like a power supply defect in the MPI. Load
> up enough devices and the MPI flakes out.
>  A good test for this is to change the order of paks and their
> positions in the MPI. For example, what happens with an MPI, a disk
> controller in slot1, the ORC-90 pak in slot4, and the MPI switch at
> slot1? If the Coco will power up in DOS 2.1, the problem is not with
> the ORC-90 pak. It will either be a non-modified MPI or power supply
> problem.
>  A test of modified vs non-modified, is to start a Coco3 without an MPI
> and PEEK $FF90-$FF99, see what the values are, plug in the MPI and see
> if the values change. If the values change, the MPI most likely is not
> modified for Coco3 use.
>  Power supply failure normally is a loose or oxidized contact on the
> main power transistor. This is caused by a screw making a bad contact
> with the transistor case. Loosen the screw/lock washer and re-tighten
> it. That should improve the situation.
>
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