Discussion about the Korg PolySix synthesizer

So I've tried to get a bit closer to possible problems and differences.

Luckily I have a few old KLM-367 and 367A here (most in various stages of
disrepair though...).

So, what could make the 8048 reset or hang (which is what I assume happens
when it jumps to A1 out of the blue)?
One possible explanation would be clocking problems. Depending on the
severity the 8048 could act "funny" or lock up.

Touching XTAL1 (Pin 2) with a probe works quite well however touching XTAL2
(Pin 3) will likely lock up the processor (as evidenced by Pin 32 losing
its pulse). Still one can measure the amplitude of the signal on both pins.

With the old boards the amplitude of XTAL1 is around 2.2 to 2.5 volts and
XTAL2 is around 2 volts or slightly below. For both my new boards XTAL1 is
roughly in the same ballpark (2.5 volts) however XTAL2 is much lower (about
1.5 volts).

I've swapped the circuit parts (X1, C22, C23 and even the processor) from
one of the older boards over to the new board; this did not change the
results at all. The value of XTAL2 stays the same on the new board.

Could this be a possible source of trouble?