I mean, the simplest answer is to lay a new cable, and that is definitely what I am going to do - that’s not my question.
But this is a long run, and it would be neat if I could salvage some of that cable. How can I discover where the cable is damaged?
One stupid solution would be to halve the cable and crimp each end, and then test each new cable. Repeat iteratively. I would end up with a few broken cables and a bunch of tested cables, but they might be short.
How do the pro’s do this? (Short of throwing the whole thing away!)
I agree. If that doesn’t work, I’d give the whole line a visual inspection for any more obvious signs of damage. If that doesn’t work there are other options to troubleshoot, but I’d probably just replace the line and attempt to recycle the old cord into shorter lines for device connections, patching, etc.