@root42 @kenshirriff My father had a PDP-11/45 in our basement when I was a kid. The CPU was a stack of perhaps 5 boards of discrete TTL chips (a few flip-flops or what-not per chip) and a lot of wirewrapping on the other side of the backplane to connect them. Next to that was the FPU, which was larger - maybe 12 boards if I remember right.
Keeping it working often meant identifying the chip which went bad. To assist with this, he managed to acquire an extender to hold a board out from the backplane a bit, which gave more room (though still not a lot of room) to clip on leads to connect to the oscilloscope/logic analyzer. However, using them required downclocking the CPU, which occasionally made the fault go away.
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