OK, here's a VAX 11/780 story. We had a 780 installed about
1980-81, it ran quite well for some time. After it was a
year or two old, it started crashing. DEC spent some time
going through logs, brought in a special team to do a time
domain reflectometry of the SBI, and couldn't find
anything. While DEC was running diags on the machine, they
had the back doors open, exposing the backplane. I started
studying the maze of wire wrap wire. Suddenly, I found a
wire that was caught on the point of a wire wrap pin. I
called to the FE, "hey, I think I found something." He said,
"don't move it" but I had already lifted the wire off the
point. The machine ran perfectly for several more years!
Jon