[Coco] Upgraded MPIs and Harware incompatability

[Bruce W. Calkins]

The first suggestion of a PAL switcher to switch between CoCo 3 use and CoCo
1/2 use seems to be Marty Goodman in The Rainbow on January 1987 starting on
page 98.  Here he does not say that the upgraded pack does not work on CoCo
1 &2s, but rather that some 3ed party hardware will not work with the
upgraded MPI.  This is the earliest reference to a PAL switcher I have found
so far.
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In CoCo Consultations, The Rainbow, April 1987 a PAL switcher is addressed.
This one is a bit vague as to the reason for the need to revert to the old
PAL for use with the CoCo 1/2
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I don't have time to research this much further now.  Suffice to say there
was some confusion as to the needs for the upgrade in the first place, and
it's affect on older equipment.

If Mark M. states the upgraded MPIs work fine with the CoCo 1 and 2, I can't
argue it.

Bruce W.