BK with a rottendog 327 pcb (revision 1 iirc). Switch matrix flipped out during multiball when all the balls were on the upper playfield. At first it appeared to be a reset issue, but the game was actually slam tilting.

Going into the switch test revealed all switches were working except column 5 (upper playfield drops and pop bumper switches). When any switch on column 5 is closed, it also closes every switch in that row. All switch diodes on column 5 switches tested ok. Removed connectors and retested at the board (jumper and diode method) with the same results confirming the problem is on the board and not playfield.

Fix: u17 on the 327 pcb was blown (available from k's arcade). Replaced and retested switch matrix at the board to confirm repair. But it's not over yet...

The real problem: what blew u17? usually it's high voltage contacting a switch under the playfield. A quick inspection revealed that the pop bumper score switch was sandwiched between the yokes (because the metal yoke wasnt installed properly) and the switch was shorted to the pop bumper bracket. Further inspection revealed one pop bumper lamp wire broke free and wasn't anchored to the playfield (evidence of a previous poor repair) The 18v from the lamp matrix hit the switch matrix through the pop bumper switch and blew u17. Two shoddy previous repairs teamed up to take the black knight down!