Hitting the lower pop bumper also fires the right slingshot, and sometimes registers the buy-in button. Switch test shows both switches closing together, but only in one direction.

One switch also triggers another: corroded switch connector on the CPU board

Cause: Old battery leakage had corroded the switch row connector pads on the CPU board, even though the game had a remote battery holder. The bad connector wasn't the one for those two switches, but the switch rows share inputs, so all of them were affected.

Checks

• Use switch test to confirm two switches register together.
• Pull the switch connectors on the CPU board and look under them and at the pads for corrosion.
• Check continuity from the connector pins to their traces.

Fix

• Neutralise and clean the corrosion, reflow the connector pads, and clean the connector pins.

Battery leakage is corrosive: wear gloves and eye protection when cleaning it, and take the board out of the game first.

Systems

• WPC-95

Games

• Jack•Bot

Related tips

• Whole switch rows read closed and U20 keeps failing: replace U23 on the CPU
• Switch matrix chips on the CPU board
• One switch does not work
• Testing CPU switch columns with the switch levels test
• Testing CPU switch rows with the switch levels test
• Telling a playfield switch short from a CPU board fault
• Many switch errors and odd behaviour after fitting a color DMD: check grounds
• Narrowing a switch matrix fault to the CPU board, wiring or opto boards

Source: Pinball Repair help group!! (Facebook group)