On my Riverboat Gambler (system 11c), switch column 7 is out: all eight drop targets do not register in Test Mode or gameplay. With connectors 1J8 and 1J10 removed the Switch Error message still shows at power up. The transistor (2N5550) for this column is R42, 1J8-8, green-violet wire. It tests good, same reading as all other 2N5550's with DMM. Logic probe shows "pulse" at U40 pin 12 (from Q42), same as others on that side.

I'm leaning toward the U40 (74LS244) or the U38 PIA (6821) as the culprit, but before I go ripping perfectly good components off this board, is there a way to test U40 and/or U38? Or should I look and test elsewhere?

Thanks in advance,

Alan

All eight drop target switches in column 7 show open in Switch Levels with 1J8 and `1J10 removed. None of the switches show closed in Switch Levels or Edges, with connectors attached or removed, targets up or down. I have continuity for the green-violet wire from the MPU to the Interconnect board input connector, to the ICB output connector and to the playfield drop target boards.

With a logic probe, "High Pulse" is shown at U40, Q42, MPU and ICB for switch column 7. "High steady" is showing at the LM339, pin 2, on each DT board.

Are you saying that there is no chance that either U40 or the PIA could be bad?