Infinity ServoStatik - beginning high channel repairs

After a couple of years, the high channel on one of the panels went out and I have some time on my hands so I'm going to try making it work.

It went out very slowly, fading in and out over a period of months, and then just completely stopped.

Is anyone here familiar with the circuitry of these ancient panels, and if so can you make any suggestions?  I haven't had any luck finding a schematic yet, just a basic crossover diagram.

There is a circuit board where components (mostly resistors and maybe a couple of very small capacitors) are covered in some kind of wax.  The most suspicious parts are exposed and easy to reach - some transformers and a couple of misc parts behind the lowest driver.

Presumably the easiest place to start is the transformers since they're easy to reach and easy to test.  Luckily I have a spare panel to experiment with (the high end on the spare panel also stopped working in a similar fashion).

Thanks,

Mark