Symptoms: black screen, no sound, nothing.
There was some NiCad battery leakage. Nothing compared to what I saw on the Sony HB-T7, and I was able to clean it up quickly.
There was no oscillating signal on the VDP’s XTAL 1/XTAL 2 (pins 63 and 64). Unlike all other retro computers I have seen thus far, this signal is generated by a 74LS628 IC on the analog board. However, it took me a while to figure out that that is the case. In fact, I did not realize this until I decided to take a look at the service manual for a very similar computer, the Sony HB-G900P, linked from the bottom of the page at https://www.msx.org/wiki/Sony_HB-G900P. This service manual mentioned the 74LS628 IC, and how to adjust it.
However, this IC wasn’t even getting 5V, and it turns out that there’s a 5V supply separate from the 5V supply used to supply power to all the other logic chips on the two boards. The IC gets its 5V through two linear regulators, first a 7809 turning 12V into 9V, and a 7805 turning 9V into 5V. The 7809 was broken with the following failure mode: up to about 10V, it output input minus 1-2V, and beyond that, it output 0.5-2V.
Replacing the 7809 fixed the machine. However, it appears that the floppy drives may be somewhat broken. I’ll look into that soon.