i've used a treedix tester like this. the edition with many led lights, not the one with a screen.
wiggle the cables around to see if and when any of the lights flicker, indicating a bad or broken connection. i've found a few bad cables that would intermittently fail.
wiggle the cables around to see if and when any of the lights flicker, indicating a bad or broken connection. i've found a few bad cables that would intermittently fail.