Hi
Glad to hear it is working. There are a LOT of parts that can go wrong on these things, but the advantage is that they are replaceable.
Failure of the NVRAM does not make the SG unrepairable/unrecoverable. A blank NVRAM and the SG will write default cal values to it by running Test 20.
The frequency audo-cal procedure figures out the transition frequencies between each oscillator, so no test equipment required. The level output cal requires a good RF power meter.
I was lucky I was able to get my SG calibrated at a calibration centre for $zero . I don't know how long the calibration will last before it drifts.
I would suggest you try the electronics department of a University if one is nearby.
If you have a spectrum analyser, you could use that to do a confidence check.
Mine past the power-on self test before I found any of the faults.
Test 18 is important because it tests the control loops. If this test fails, the SG is seriously ill.
The internal inverter to drive the display back light is quite weak. I think this was probably a design feature to extend the life of the back light. This is consistent with the backlight on/off switch on the rear panel. I would describe the back light as adequate. Not great, and not bad. It works as designed, and that is good enough for me. Most importantly, it looks cool