Phonoland

The drum is non-responsive when any of the first four category buttons are pushed. The fifth category button (the one on the far right when facing the machine) seems to work fine. I've removed the drum and inspected the switch bank on the far left side, and everything appears to be adjusted correctly. Any thoughts?

I would guess that the category switches ( ones used by customer), have an open in the circuit--can be in the plug, also.

As Ron pointed out, it is the button switches.
The circuit daisy-chains through the 5th switch to the 4th and so-on. If a break in continuity occurs at the out position of a switch due to pitting or broken slide contact all the categories to the left of that switch become unavailable.

Aside from a-hole kids punching the buttons for fun, the AC drum motor draws just over 3 amps through the switch contacts and they arc as soon as they lose a bit of tension due to use. This eats away available conductive metal and eventually you have an open circuit. The sliders can break off as well.

I solve the current problem by using a 24 VAC relay to operate the motor and this reduces the switch current to around 30ma.

When the contacts break off or the phenolic simply falls apart I have to make a new one from switch parts I bought back in the 80's here in NYC.

I can see why so many of these machines were "Wico'ed".

Rob/NYC