Since the keyboard I had was missing some keys and was acting very non-keyboard-like, I procured a replacement on eBay, which happened to come up at an opportune moment and not cost very much. It was untested, apparently the seller still had the keyboard but no longer had a computer to test it on. But it looked nice, both in the auction, and once it arrived. And, moreover, it seems to mostly work.
It was certainly able to take me into service mode, which was what I was hoping for, so that I could look at where the RAM problem was. I tried all the alphabetic keys and they all seem to work, with the exception of “A” and “J”. I’m going to probably need to address this keyboard by replacing the foam backings on the keys, but now I at least have two keyboards to work with, in case spare parts are needed.
Having taken the Lisa into service mode, I was able to see what chip it thinks is bad, thanks to this extremely helpful post on LisaList by James MacPhail.
According to the diagnostics, the chip on memory card 1, row E, column 1, is faulty.
Looks fine to me, but, nevertheless, I downgraded the Lisa from being a 1MB machine to being a 512KB machine. I have no way to fix that RAM chip right now, but I do have a way of taking it out of the machine.
And: success! Sort of. No errors, this time. Just no boot disk. I tried again putting the Mac 512K boot disk in, but again the drive whirred a bit and then just spat it out.
So, the next thing I’ll try is using my Duo 2300c and accompanying 3.5″ drive to see if I can make a disk the Lisa can boot from. I set up the machines, but the trial itself will need to wait for another time.