At this vintage of machine we're talking about things like pulling individual RAM chips which have gone bad, and hardware that is just too slow to even keep up with 9600 baud datastreams - despite the fact you wrote it all in assembly and hand optimized it.

Not to mention the fun of playing with front panel switches. I built an emulator for one long before I acquired my IMSAI. They did not behave at all how I expected. Even more interesting the front panels are not synchronous on these "hobby" machines from the 70s but instead are timed by RC circuits that are supposed to be "close enough" to the CPUs clock.

Not all of these problems are from age (although that has an effect), the hardware was pretty flaky even when new.