In the in-order drop target bank, target 4 never counts once it's the lit target, though it always shows in switch test. With target 3 down, 4 won't register, and the other way round.

Fourth drop target won't count when lit, but works in switch test: MPU fault

Cause: A fault on the replacement MPU board (probably a PIA input) making two switches interfere.

Checks

• Switch test shows only the lowest-numbered closed switch; check whether a second switch is being seen at the same time.
• Swap the two target switch wires: if the problem moves, the switches are fine.

Fix

• Fit another MPU board (the original fixed it here) or repair the PIA side of the faulty board.

Systems

• Stern MPU-200

Games

• Cheetah

Related tips

• MPU LED never lights at all
• Seven flashes but no attract mode
• Dark MPU LED: follow +12 V through R29 and Q2
• Intermittent MPU faults from old closed-frame chip sockets
• M-200 flashes seven times but the game misbehaves or repeats one number in audits
• Testing an MPU in the game with only J4 connected
• MPU board test points
• MPU board test point voltages

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