Finished recapping the transport. Tantalums were replaced with tantalums. The three electrolytics were replaced with three modern ones. I also reseated and cleaned a few ICs. Why not?
That mod that was done – seems like someone tried to avoid rewind or record functionality when the machine was set to AUTO. Nothing in the manual matched that mod, so I jumped the broken traces. Forgot to take pictures, but it looks good! I also lubricated the switches with Caig’s F5, and they don’t squeak as much as they did.
Put the transport back in the machine, fired it up, and god dang it – the motors spin, -12V rail pulled to 0, but the transport is reactive.
I tried isolating the problem by disconnecting different parts of the machine:
Disconnecting “To Audio” and “To Transport” at the PSU gave back the -12V rail, and only the take-up motor was spinning.
I disconnected the two at the transport the connectors that carry -12V to it, and the motors don’t spin but the -12V rail is still pulled to 0.
That led me to think that maybe something is up with the wiring, because disconnecting the voltages at the PSU brought back the -12V rail, but disconnecting it at the transport did bupkes for that rail.
Not sure why, but it the dawned on me to disconnect the Capstan Speed Control, and hey! -12V rail is restored, supply motor isn’t spinning (take-up was), and the supply behaves in accordance to the transport button. So I think something at the CSC board is pulling the -12V rail down. Will recap it next!
Disconnecting the two connectors that carry the -12V rail to the transport stopped the motors from spinning, but the rail was still pulled to 0. Disconnecting the “To Audio” and “To Transport”