The diagnostic buttons on my Funhouse started acting up. The service credits / back button is acting as the volume / down button, and activates repeatedly after being pressed. The volume / down button doesn't seem to function.

No visible shorts or loose wires at the button or the coin door board. Diodes at the coin door board are good.

I'm thinking since two switches seem to have failed / combined at the same time, there's probably a board issue. When I look at the manual the diagnostic buttons are on the switch matrix chart for Funhouse, but they're off to the side as "dedicated ground switches" rather than having a column and row. Manual is a little sketchy.

Do the diagnostic switches get routed through an IC on the MPU?

------

Update (in case anyone ever comes back to this with the same question):
The diagnostic buttons are not really part of the switch matrix. But they connect to the MPU on J205, and are controlled by transistor U16 on the MPU. The issue is likely a failure at U16, but it is not proven because in the end corrosion damage was demonstrated so I just replaced the whole MPU.
Page 3-16 of the manual notes wire colors.

Looks like trace actually is fading in spots. I might replace the mpu instead.

I'm definitely going to swap mpu with my new addams. I don't think the connectors need to be repinned to match, the aftermarket MPU I have says it's compatible, but I'll double check. I honestly didn't notice the board jumpers before. They were sort of bundled with the remote battery pack and I thought they were one and the same. I bet there's a relationship between the misbehaving switches and those, they'll belong to J207 I'm sure.

That's perfect, thank you! I missed that page.

Diagnostic switches do go to "Transistor" u16, which is an IC, and behaviour does seem like a failing IC.

One of the wire bypasses isn't used. Mystery to me why it's there. Only 7 of the 8 columns seem to be used in the game.

I think any corrosion on the board was halted with vinegar long ago, up close there's really no green stuff, it's all coppery. But I still think I'll repin J207 back to stock and swap in my new Addams MPU. I've already made a deal for the game and don't want any potential failures in the near future, would rather a happy pinball friend with a solid machine.

A project for some other day (year). I'll probably throw the board in my to-do box and order a new one to replace the one I'm plundering.

I appreciate all this help, thank you very much!

*** Everything is gold after MPU swap.