My experience with music boxes is limited, but I do work on lots of
clocks.  The term "stopwork" denotes any mechanism that restricts the
winding-up or running-down of a machine powered by weights or springs.
Some grandfather clocks, which are powered by weights, rely on stopwork
to keep the weights out of trouble.  Some spring-powered clocks do the
same to ensure that the most linear portion of the torque vs. time
curve is employed.  This improves the accuracy of the clock.

But in the case of a music box, the stopwork would be used to prevent
a disk from re-starting after it reaches the end of the selection, and
also to prevent strain on the winding mechanism and mainspring if the
operator is overly enthusiastic.  And, stopwork will also ensure that
only the most linear portion of the spring's torque vs. time curve is
employed, which will ease the job of the speed governor.

Aside from this last point, I can't quite understand how a lack or
malfunction of stopwork would cause a disk music box to stall when
many notes are being sounded at once.  That particular symptom would
seem to be due to a lack of torque (or, power, if you will) to whatever
mechanism drives the hammers.

In a clock, we'd look at the condition of pivots, for a pivot that has
elongated its hole may cause gear teeth to mesh incorrectly and lose
power through friction.  Failing that, there could be a bent pivot or
a slightly bent or otherwise-misaligned movement plate.  Lubrication
might also be a factor, but seldom is.

As for the 'cacophony,' it's not clear if notes are being played out
of sequence, or simply too quickly one after another.  If the latter,
we'd try to figure out what's causing the mechanism to leap forward.
In any of this, we'd want to take a close look at the speed governor
and the gearing that surrounds it.

Mark Kinsler