Just reviewed my previous comments and have to laugh. "Oj"? and how does one "watch a sandwich"?
(Would be nice if this forum offered an edit feature but..oh well..) Anyway, thanks to all who offered help!
Per the thread, I have swapped mostly everything from the good machine to the bad machine (and back) and the results are the same: the described failure. There are times when the bad machine "wakes up" but it always reverts to form. As for the four drives --
A: and B: on the good machine and A: and B: on the bad machine -- every permutation has been attempted with no success. That is the bad machine drives swapped to good machine and the good machine does not fail. Good machine drives swapped to bad machine and the bad machine fails. Same with B: for A: and A: for B: with no success. (Jumpering and resistor plug "settings" observed.)
Also, did you know that the A: power plugs have a different wiring than the B: plugs?
At the moment (well, tomorrow), I will be examining the DC wiring harness to check for intermittent/faulty connections and do a diagram. (See comments re Kaypro "tech manual" below.) I doubt I will find any problems.
But I am going to double back and focus on what the WDS1793 FDD controller tells me. Don't know what I'll find . because I am still digesting the datasheet. But we shall see what we shall see; it'll be an education.
Final comment on the "Tech manual" Kaypro produces. I have a lot of Tek[tronix] stuff on the bench (an old Tek 7704A scope and plugins) and have the service manuals to go with them. Clearly, the Kaypro tome is not up to those standards but it needn't have been. The manual was loosely put together from scribblings and notes from the Kays at NLS and meant to be hints about what's going on for the techs in the field. Not sour grapes on this; just realistic. But anyone engaged in endeavors like this should not expect the Encyclopedia Britannica or the like.
I don't; and that's why all y'all's help is greatly appreciated. Besides, the research is half the fun!
Probably offer up these two machines for parts or repair down the road. Think I'll get me a Raspberry Pi and do some Linux development work!
Thanks again!