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Testing a screwy Akai GX286: what should I be looking for?

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This is a machine I cleaned completely and then recapped (taking it very slowly) and now I am at the testing stage. I'm pretty new to this, it's my first recap, so still getting to grips with reading schematics, looking over the board layout diagrams, and other things.

The deck had playback issues before recapping, going into reverse, stopping, and if I recall, going into wind or rewind. First thing to mention is that the operating buttons are touch buttons, so that's one potential area of complication. The original wire connections to the metal terminals that screw onto the back of the solid metal buttons seemed okay but a bit fragile looking, so I took a mm or so off the ends of the wires, then resoldered them back onto the terminals. The buttons are basically operating as explained below - the issues are the same both before and after resoldering.

Also, I have replaced the relays on the relay board with new relays, but have the originals which I can put back if necessary once I open them up and clean them.

When I load a tape, playback seems to be working fine both in forward and reverse. Speed switching between 3.75 and 7.5 ips also works. However, FF and RW don't work at all, what should be FF simply stops the tape, RW does nothing, and the stop button does nothing. When the end of the tape rolls off the playback reel both reels go into fast spin. I can stop that by hitting FF, which as I mentioned is behaving like a stop button at the moment.

I can also get the reel tables to spin by lifting the arm assembly connected to the brake solenoid plunger, operating the microswitch. I have made the brake solenoid position and switch position adjustment specified in the service manual, but the solenoid itself does not seem to operate: no movement and no sound. With a multimeter, I measured the AC voltage at both the pinch roller solenoid and the brake solenoid terminals, they are near-identical at 110.8 and 111V.

Assuming it's permitted, I can post grabs from the service manual if anyone needs to see board layouts or other info.

Any suggestions on what I should be measuring first? I very briefly measured DC output voltage on a couple of the button circuits on the touch button board, but I didn't much understand what I was seeing, or what I should be seeing.

(By the way, there are no 2SC458 transistors on this deck, so nothing to replace there.)

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