I think that the best way to approach this (sez an elderly clock
repairman!) is to assume that all the adjustments were adjusted
correctly when the thing stopped working, which means don't adjust
them until you know what they do.  What's very likely wrong is that
the mechanism is dirty.

If it was a clock, what we'd do is to gently let down the mainspring,
however that can be done.  Then take lots of photographs of the
assembled mechanism and then more pictures as you take it apart down
to its little gears.  Dunk the whole thing into a cleaning solution
which could be charcoal lighting fluid, or ammonia, or Simple Green
degreaser, or take it to someone with an ultrasonic cleaning machine.

Remove the mainspring carefully and keep it out of the cleaning
solution; the mainspring can rust.

Rinse the parts if necessary -- rubbing alcohol is my favored rinse
-- and then let everything dry in a bowl set beneath a hot light bulb
for maybe an hour.

Re-assemble the cleaned mechanism and note how much shake the gear
axles have in the little holes they ride in.  If the holes are worn
oval, then the gear teeth cannot mesh properly and other measures like
the installation of bushings must be taken.  But if the holes are okay,
clean each one out with the point of a toothpick and, after the device
is laboriously assembled, put a tiny dot of oil on each pivot.

Be careful of the mainspring if it's a big music(al) box: these things
store a lot of energy and are always delighted to release it at
inopportune times, thus causing injury to equipment and to you.

Mark Kinsler
Lancaster, Ohio, USA