Sharp GF-990G tape decks not working properly

I recently obtained this beast. I took a bit of a punt on it, not knowing whether or not it worked. To my surprise, it mostly worked fine.



The synth keyboard, the radio and the speakers all work fine. The only issue is with the tape decks. Initially the right deck didn't work at all, but I managed to free it up and it now does something, at least. Essentially, both decks have the same problem - they play, but the take-up spindles don't turn, so the tape just piles up.

There are various screws missing, so someone's had this open in the past. I'm wondering if they didn't configure the belts properly. The problem is, I am an ignoramus and don't know how they should go.

This is how they look at present.



The motor pulley sits on top of this, near where the 'sharp' logo is, and the big belt - I assume - goes around it. But when I do that, I get the aforementioned problem.

I have the diagram from the service manual, but it doesn't mean an awful lot to me, because, as I say, I am an ignoramus.



If anyone can offer me some advice on how to get this hooked up and working, I'd be very grateful. I'd love to get this machine going.

Finally, here's a couple of gratuitous photos of the innards:





Thank you.

Look for any wheels with tyres on them and give them a clean with a cotton swab.
Also look for the brakes which usually sit on the spindles/reels and stop them turning, make sure when play is pressed that the brakes are raised.
When you turn the flywheel manually you should be able to work out what it is that turns the spindle/reel.
Often there is a mechanical reason but do not discount stuck gears which need removing and old grease clearing up so the gear turns smoothly again.