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Problem with autoreturn of tonearm

Hello everybody! :-)
I have problem with my second hand Pioneer turntable. When autoreturnmechanism is activated and tonearm is raised and begin to return nearthe periphery the stylus make contact with the record and pass alongit, and thus scratching the LP :-( I try to do better balance ofthe tonearm, but it didn't help.
What' s the problem and how I can fix it? Is it due to incidence of thetonearm support and if this is the problem, how can I fix it?
Thank you very much for the assistance!
Vence

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This very much depends on the type (and vintage) of the
turntable.

Very old turntables used a system of mechanical CAMs,
slaved to the main plater. Once engaged (usually through
a hinged/retracted gear-tooth), the platter would spin the cam,
which in turn would lift the tone arm, move it back home,
shut off the power and disengage itself after one complete
revolution.

This system could be mechanically triggered with the power off,
just by swinging the tone arm towards the center, and spinning
the platter manually by hand. To fix it you had to make internal
mechanical adjustments, or replace worn out levers, wheels,
bearings, springs, etc...

A more modern turntable will use electrical sensors,
such as a micro-switch under the tonearm gimbals,
which is triggered as the tonearm swings towards the center.
A second switch is coupled to the stop/ return button.

Once the mech. is triggered, it can derive its power from the
plater (as before) or use a separate servo motor to lift
and return the tone-arm. The viscously damped cueing
mechanism can also be involved in lifting the arm during
the return cycle.

At the hi-tech extreme, a microprocessor can control the
whole works through the use of selenoids and stepping
motors with optical or magnetic sensors to trigger it,
position it and disengage it.

0) Note:
During all testing, remove the record and cover the
stylus with its protective gate to prevent damage.

If the stylus slides out of the cartridge, like it did on the
Shure cartridges, remove the stylus gently and put it in
a safe place to avoid damaging it. You do NOT want to
ever drop the stylus on the spinning rubber platter surface.

But leave the main head and cartridge in place for normal
tone-arm balance.

Turn off your amplifier, or turn down the volume to zero, to
prevent damage to your ears and the speakers if the needle
does fall when it shouldn't

1) Assuming that this is a fairly modern turntable, with
a gimbal mounted tone arm (the large double hung ring
bearing at the back for swinging both ways) and a
counter weight for setting the stylus pressure...

and possibly an anti-skating adjustment as well...

It is fair to assume that the cuing lever is what lifts
the arm vertically, regardless of the swing return mechanics.

2) The premature stylus drop (during return) is therefore
caused either by a cuing defect, or by lift timing,
either mechanical or electronic.

The stylus weigh setting is NOT an issue here, that
is determined by the stylus and cartridge specifications,
and must be set correctly to prevent record and stylus
damage.

Note that both too much and to little weight is BAD.
Too much weigh is obvious, but too little will cause
mis-tracking, distortion and premature record wear.

Similarly, and incorrect tracking pitch or yaw will also
cause early damage, as will incorrect anti-skating for
a particular stylus pressure.

3) First of all, test the cuing lever at several different tone-
arm angles, to see if it stays up, or droops down with time.

If there is a problem, check the springs, viscous damping..

Take the ****** apart from below, and see what gives.
Is it mechanical, hydraulic, or electronic ?

4) If it is electronic, you have a control/ timing problem,
which requires a service manual and a qualified electronic
tech to fix it.

You should be able to check any sensors, switches
or motor yourself, though.

5) If the cuing lift system is mechanical, check the levers
and cams:
What is driving it ?
Is it broken ?
Is worn out ?
Is it out of adjustment ?
Is it slipping ?
Is it stuck ?
Is one of the springs all stretched or missing ?

6) If the lift is hydraulic or pneumatic, check for leaks.

7) If the manual lift seems to work, but the automatic return
drops it...

why?
what is controlling it ?
how is it linked it to the arm return mech ?
Is there a coordination/timing problem ?

Have fun.
Please rate my answers.

Martin.

Posted on Jul 01, 2008

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