Not sure this will work but it is worth a try as a test of the autoformers.
As I understand them, they are one coil with multiple taps, input and a few outputs for different impedances.
First, you want the amp unplugged long enough for all caps to discharge.
Take a small, low power amp and hook a sound source to it, MP3 player, phone, cd player, tuner, it doesn't matter. Using a 4 ohm resistor to make sure that there is a load on the amp, hook one channel to first the 4 ohm resistor then to the output of the autoformer. This is a series circuit, that is positive on small anp to one side of resistor, other side of resistor to positive 8 or 16 ohm output of autoformer, common terminal of autoformer back to negative terminal of the small test amp. Play some music and hook a speaker to the common terminal of the autoformer and ANY other terminal of the autoformer as long as it is NOT the one hooked to the resistor. IF the autoformer is good, you will hear music from the speaker.
This is similar to checking output transformers in a tube amp.
Good Luck
Shelly_D