[MrFixr55]

Hi Klondike,

Here is my contribution to the "Things I really messed up" thread:
Years ago, I attempted to repair a power supply for an HP 2225 computer terminal. Had no schematic for it. Found a Zener diode across the 5V power supply, shorted. OK, I'll just "dike" (cut) that out with my diagonal cutters, power it up and see if that fixes it.

OK, it didn't blow the fuse, but no vid-, oh what's that crack, crack, crack noise. Oh look, all those chips look pregnant! Oops, smoke!! Then the output filter cap blows off the board about 8 feet, trailing confetti behind it. My coworker is out the door about to pull the fire alarm; I wet myself laughing.

Post-mortem, this was a standard for the time, analog regulated power supply, 15V in, 5V out. The pass transistor had shorted, putting 15V out the 5V terminals. That had caused the 6V Zener diode across the 5V output to short, taking out the fuse. When I diked out the Zener and replaced the fuse, I put 15V through the whole 5V logic circuit.

Made the terminal disappear.