Vintage Synth Repair

Both of the "Fuzz Guitar" presets behave oddly. It seems like they
sort of "cycle through" slightly different waveforms. Sine, square,
saw, etc. Abruptly, almost like someone reciting vowels. also, Fuzz
Guitar 1 is kind of quiet, while Fuzz Guitar 2 is really loud.

Could be normal behaviour.

I recall from several Pro-Soloist and Pro-DGX that there was a very
noticeable difference in loudness between both Fuzz Guitar presets.

As far as the "stepping" of the waveforms goes: This is probably also normal.

Both presets (and a few others) use the "dynamic pulse" setting;
essentially the  implementation of PWM for the Pro-Soloist. The "dynamic
pulse" is derived from the sawtooth wave.
The following is from memory: I recall the sawtooth not being a "smooth"
sawtooth but a stepped one (because it's actually built out of a number of
pulse waves with different pulse widths). On the oscilloscope it looks like
a real staircase. So if this wave is "scanned" by the ADSR there naturally
will be some stepping.