Ah, glad I may have been some help. I own 3 SQ-A bodies, one with an unhappy shutter release, and 50, 65, 80 and 110 1:1 macro PS lenses that I hope to be able to keep going with for a decade or two, but there isn't (that I've been able to find) much info around on what goes on inside the boxes. Someone pointed me to a service manual .pdf file for an ETRSi, which I downloaded, but it doesn't appear to cover anything but the body itself, which is only a portion of what's happening.

The combination of irregularities you describe doesn't quite make sense to me, weighed against what I 'think' I understand about the little buggers, but that may mean, Zeus forfend, that my understanding is incorrect -- not that that has ever happened before .... Hopefully APUG may become a 'knowledge base' for some of this stuff as time goes by and we decipher things.

I suspect that some "data parameters" might be communicated via analog current or voltage in these beasties, since the design is pretty old. There are only a few contacts connecting the back and viewfinder to the body, implying a serial communication, although I guess it could be some sort of crude digital as opposed to analog serial hookup. I'm thinking an analog method might rack up extra current drain at one extreme or the other for ISO and light measurement. As a long time tinkerer in many fields, both hobby and professional, I own an oscilloscope and a few other things that might permit some deeper investigation -- "one of these days."

I often tell myself "sometime in the winter, when it's too cold to be doing stuff outside, I'll dig into [insert object here]" but here it is February and I've got a million things going on. (Maybe I need to switch to "summer when it's too hot to ...")

Anyway, good luck with it.