...
Next measure: PA1_ (U5P1, purple) and PA0_ (U10P11, blue):
...
PA1 is zero’ish, but PA0 (blue) is hovering in the middle.
Next measurement: on CPU board, measure U1P4 (PA0 cpu, yellow), U1P6 (PA0 buffered out, purple) and Tape board U10P11 (PA0 directly from CPU U1P6 (resistance 1.6 ohm):
...
All nice voltages and all nicely 1, oddly enough, so the earlier measurement must have been in error 8-(
Sending a “REW” with the same assignments does drop PA0 and this percolates proper:
...
Remember logic is inversed, so addr 0x1 would indeed need to drop PA0_- as it seems to do.
And of course- when I do the “rew” now it reports “Error 41” - No cartridge in tape unit, sigh.
Cause: bad contact on the flat cable connectors, most likely.