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  It was shorted, and has been replaced by a comparable ceramic cap.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…