Manhattan, IL
Quoted from Allingerb:I shorted something with the jet bumper on black Knight while adjusting it's switch under the playfield and jet bumper no longer works. I'm trying to fix but can't find the problem. I've been testing about everything I can think of and so far all I know is that this chip gets very hot very fast if I turn on the game. If you have insight as to why, I would greatly appreciate it.
The heat is a pretty big clue something may be wrong with the chip. Hard to tell from the photo, but looks like a 74HCT06 or 08. You can do a quick test as per this procedure...
https://www.pinwiki.com/wiki/index.php?title=General#Testing_an_integrated_circuit
Very common and inexpensive to acquire.
Accidentally sending high voltage from the playfield back into the MPU is something that has happened to me. Typically logic chips on the MPU such as your 74xx are the first thing to take the hit. The chip gets fried and passes most of the current to ground. Let's hope that's all it is, and that it did not blow out any of the more expensive chips.
Quoted from Allingerb:I think my pliers hit the power from another coil. The jet bumper is no longer working. No sparks or smoke but one of the coils fired when it shorted.
You aren't necessarily going to see sparks or smoke. Sparks and smoke require a lot of current. This happens too fast; the chip(s) get blown out before any substantial current can pass... after all, you can blow a logic chip with static, which has an extremely tiny amount of current.
Quoted from Allingerb:The game was still working minus the jet, until I pulled that chip and swapped it with an identical and then discovered it's cooking. I'm so stumped.
Multiple chips could be involved - and if you created another fault elsewhere, you may have instantly blown out your replacement chip.
You're going to need to examine your schematic. Trace back the path from where you think you shorted it out. When I blew my switch matrix, I knocked out a 7432 along with a 7400... luckily they stopped it because the next chip was a RIOT. Looking at the schematic, it was obvious which chips were involved and which gates on those chips were blown.
