Check your coin switches. Make sure no part of those switches are shorted to the coin door.

Usually when this problem happens there is a shorted diode in the switch matrix. The rectangle technique is used to troubleshoot a diode issue.A0735457-703B-4552-ABDF-D75C6366FB3E (resized).png
We know the tilt and “A” standup are two “corners” of the rectangle. Looking at the Kiss switch matrix you’ll find these two switches on the same row, in columns ST0 and ST1.

That means the other two corners of the rectangle will also be in columns ST0 and ST1. For the problem to occur, three of the switches in the rectangle have to be closed for the fourth (tilt in this case) to trigger.

Since this is a single ball game there are no balls sitting in locks or in the trough holding switches closed. The only other switches that can be held closed are the drop targets.

All four drops are in column ST0 with the tilt switch, and only one can be a corner of the rectangle.

We need to find one more switch in column ST1 that could be closed to complete the rectangle. Coincidentally, the switch with the shorted diode will be the switch on the opposite corner of the rectangle as the switch that’s malfunctioning.

Three possible rectangle switches in column ST1 are the coin switches. The fourth is the “D” standup. I suggested the coin switches because it’s easy for them to be mangled and short to the coin mech or door, which is grounded. The “D” target could have a shorted cap and cause this too.

An easy test would be to start a game, knock down drop targets one at a time, hitting the “A” standup after each one. If it tilts the problem switch is in column ST1 on the same row as the target that was dropped.

Is that the top drop or bottom drop?

Check the coin switches. No diodes on these so a stuck switch would cause this problem. Also look to see if anything is shorted to the coin mechs or coin door.