Progress continues. I tested the regulators and they were fine. I ultimately traced the problem to C513. It was shorted, and has been replaced by a comparable ceramic cap.
After bringing her up on a variac, I’m greeted with an H: prompt!
I ran a memory test, which is one of the routines in the monitor ROM. A full test would take over 2 days, so I just let it run for a bit after quitting.
377377 is 64K in octal.
There’s a routine you can enter manually that prints characters to the screen:
Finally, there’s a routine to run a drive speed test. Using a tweaker to adjust to 200:
Unfortunately, I can’t get it to boot off any medium I have, either hard sectored on the built-in drive, or soft sectored using the external H77 drive. Not sure what to try next…