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MMD > Archives > September 2011 > 2011.09.23 > 02Prev  Next


Repairing Thorens AD30 Disc Musical Box Movement
By Don Caine

Hi Josh,  in response to your inquiry in 110922 MMDigest regarding the
Thorens AD30 movement.

First, please understand that the on/off (or stop/start) mechanism
is not an immediate reaction type of situation.  From a stopped state,
pushing the lever to START will start the mechanism.  However, then
pushing it back to STOP will not immediately stop the motion; it was
designed to stop after one full revolution of a disc.  (That rotation
time should be 19 to 21 seconds.)

Second:  Loosening the swing arm is likely to only make matters worse.

Four thoughts as to the possible cause of the problem you are
experiencing:

1. If the mechanism was not sufficiently wound up, the mechanism would
not have had enough energy to drive the discs around.  Be sure you are
initially winding the mechanism up fully, until you meet major resistance.
After a full wind you should be able to play 6 or 7 records (revolutions)
before the mechanism noticeably slows down and then comes to a halt.

2. Before playing the mechanism for the first time, run your thumb
along the star wheels to bring them all into a single line (alignment).
Not doing this may cause the records to pop and click on the first
revolution but the wheels should self-align and there would be no
popping or clicking on the second revolution of the same disc.

3. If some records are sticking and not others, check the teeth on the
bottom of the discs that are sticking to see if they are bent or twisted
as that can cause the mechanism to bind up and jam.

4. Lastly, depending on the age and technical construction/design of
your AD30 (small changes were made to the AD30 units over time such
that movements made in 1930 are considerably different than ones made
in 1950 and the ones made in 2010 are again somewhat different -- see
http://www.ThorensAD30.com ), the most likely problem with your machine
is that the block holding the star wheels (that pluck the notes on the
comb) has begun to warp and/or crack and therefore the teeth on the star
wheels no long align perfectly with the teeth on the underside of the
discs.  Thus the teeth on the discs jam and cause the disc to stop
rotating.

If that is the case, the solution is to replace that star wheel
assembly and possibly the swing arm too.  If your mechanism is one of
those with a solid swing arm vs. the newer version that has a tension
spring and two cones that ride on the disc built into the swing arm,
the arm will need to be replaced because the replacement star wheel
assemblies were designed for that newer swing arm.

Please call me to further discuss and diagnose you particular mechanism
and its needs.

Most sincerely,

Don Caine - The Music Box Repair Shop Unlimited
Lomita, Calif.
tel.: 1-310-534-1557


(Message sent Fri 23 Sep 2011, 21:42:55 GMT, from time zone GMT-0700.)

Key Words in Subject:  AD30, Box, Disc, Movement, Musical, Repairing, Thorens

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