Some of the keys stuck, or didn't play, or played badly. I blamed the spring contacts behind the keys, so I immediately set about tearing the thing apart.
Step 1: General Warning
Step 2: Digging In
The tremolo is a speaker set behind a rotating foam wheel with a large slot cut out to make the sound wobble in that particular way that pipe organs do.
Our wheel didn't spin. To make it do so, we spun it manually, dislodged the nut placed on the rope, and that was all it took.
Step 3: The Keyboard.
First, the wood covering on the top has to be removed and the situation assessed.
Our top rank had a series of spring contacts which were moved by the wires protruding from the back of the wooden keys. The contacts were arranged with one, two, or three springs per key; and each set had a spring and two runners that all needed cleaned.
Meaning: I had a lot of contacts to clean.
Step 4: Cleaning
Step 5: And Cleaning..
Be sure not to break any wires, or there's no telling what will happen.
Step 6: And Fixing
One had come off and needed fixing. Unfortunately, it was on the bottom rank and needed to be fixed blind.
Step 7: Reassembly
Thread the springs through the correct holes in the plastic movers and put the key wire back on the plastic strip as well.
Step 8: Hope and Test
Was that screw you found you left out critical?
No way to tell except to put it together, plug it in, and play every key to test it.
If a key still does not work, bend the wire on the back of the key up a little to get better contact between the spring and runner.
If no keys work, good luck. It's probably dead.