Repair methods (was Cromemco 3101/Beehive B150 score)

That is _exactly_ what I object to. Fault finding is not (or rather should not) be bbased on guesswork. Unless you've found the fault logically, you can't know you've fixed it. I've got stories of where a problem in one module appeared to be cured by replacing a different one that was, say, more tolerant of timing errors on one of the signals. Of course the problem came back as the timing error (which was the original fault) got worse. And this is one reason I don't have a modern computer. I don't have (and can't afford) the necessary test gear to be able to _prove_ which module is at fault. 'Digital circuits are built from Analogue parts' (one of Vonada's lawas IIRC). I haev never understood how you can understand digitial electronics properly and not understand analogue electronics. I certaimly couldn't understnad digital stuff until I understood things like transmision lines, termination, etc. I think if I had a machine like that to maintain, I'd make up a test rig, with a power supply giving those voltages. To be honest, I don't care too much about the appearance of the components, provided they are electrically correct. There are certainly a few obvious modern replacements in my 1968 HP9100B. -tony