Hi JG,
I guess I should read more than I write, but this one item caught my eye.
You talked about read data coming out of an SA801 drive when there was no disk in the drive.
Just to confirm you are not crazy (or ... both of us are) I saw the same issue with data coming out with my drive door open on an SA800.
I believe I was measuring the digital TP16 + Read Data on the board.
I have two drives, was just running one, and connected up the second and the data did not seem to be there.
I glanced at it with probe 2, believe it was on auto trigger, and didn't see any pulses
(probe 1 was intended for index, trigger, but was not connected)
Drive 1 went to the side (though I still do not have much success with writes to drive 2).
I will go back to my drive 2 and confirm there is no output triggering just on the TP16.
(maybe there is something gating the TP16 to the drive interface if there is digital noise...)
Will let you know.
Al