Two dead LK201 keyboards

Gentlepeople, I'm doing some work with my Pro 380 over the holidays, but have run into a snag because both my LK201 keyboards are dead. They fail poweron self test -- LEDs stay on and no response to any keypresses. The odd thing is that the circuit board itself seems ok; I had a spare board that tests fine by itself, so I installed it as a replacement control board on one of those keyboards and now it fails. So that suggests there's something wrong with the key array that breaks selftest. I don't understand that because the documentation says a stuck key would produce a selftest pass along with an indication reporting stuck key. And while I know LK201 keyboards don't like spilled liquids, one of those keyboards definitely hasn't been abused that way and I don't see signs the other one has, either. So having both fail the same way is puzzling. Any ideas?

I'm considering building a PC keyboard LK201 emulation, should be a fairly simple bit of Arduino code.