With my neck in a brace from the whiplash I got when I opened the mailbox earlier this afternoon to discover the replacement AC adapter I'd bought on eBay on Saturday had arrived(!), I am sitting here running a standard U.S. English installation of OS 7.5 on this 550c from the 12-disk set (dated 1994) it came with in addition to the 27-disk Japanese OS it's made for. So obviously, the adapter is the solution (at this point) to at least the primary problem. I won't know if there are other issues until I am working in an OS whose language I can actually read. As in the Fall, when it was running after I first got it, the screen backlight seemed to go off on a consistently quick interval. I'm not sure if this may be some display setting in the Japanese OS or some wacky 3rd party extension for saving battery power (it's on the AC adapter), or something else that's problematic. It hasn't happened at all during this floppy-disk booted installation. Was just looking thru my Color Classic running 7.5.3 and the jury is still out, there are some OS items that must have been trashed by the previous owner. And I am now reminded that there are two very slight nicks on the screen plastic in the lower 1/3, not horrible but slightly noticeable on an even-valued background pattern, which is Installer gray at the moment. And that the very top corners (1/2" square) are slightly darkened, - is this perhaps darkening from the heat of the backlight source over time?
The installer just asked for Disk 6... Disk 7 is the last of the regular installation, after that it's PowerTalk and QuickDraw GX which I think I'll skip for now while I'm ahead.
I might not be editing my signature quite as soon as I thought...