Thorens TD 128 MkII. Clutch or no clutch..?

[samjmann]

Hi all :)

I've worked on one of these decks recently where the motor would not turn due to a fault on the motor control pcb. This was fixed by replacement of the op-amp
IC's in the speed control circuit. (LM324's). After this the motor speed is spot on, however.. there's another problem 'belt-throwing'

After fitting a replacement belt there's a tendency for the belt to come off on start up. The motor aligment is OK. The problem is caused by the motor juddering slightly on start-up. If the belt slips on the motor pulley on start-up, the belt stays on. If however the belt is new; and has plenty of grip to the sub-platter and motor pulley; the motor judders under the load and this throws the belt! There's a few posts on other forums regarding this, one even mentions the use of talc on the belt to reduce the amount of friction on the motor pulley!

I read on one posting that the motor has a built in clutch, and after the unit has been in storage for years, this can seize. Simply putting the motor on 45rpm and then stopping the motor by hand releases the clutch. I've done numerous times, but the motor pulley seems firmly bonded to the motor spindle. A clutch would certainly keep the belt on, but I don't want to damage the motor as it might not have a built-in clutch by stalling it any more!

Anyone had any experience of this on these decks?

Best regards and thanks for any help or advice given. :)

[DSJR]

Don't know these very well, but if there's a clutch it'll be obvious (nylon/delrin pulley and it's sort of spring loaded on the brass clutch-plate (if the 160 series and siblings are anything to go by).

I just ought to ask if the belt is actually a proper Thorens one? Some of the cheap equivalents look the same, but use a much harder rubber compound. Official belts have 'Thorens' printed on the outer face.

In the case of the TD150 and 125mk1, the belt had to slide on the fixed metallic pulley and only dropped off if old and stretched (you can't change to 45 either when the belt is too stretched).

I'm so sorry, I can't offer any more. Failing everything, a dusting of talc on the belt may well help rather than hinder here. Check with UKD, who I think are still the UK agents for the brand :)

[Rare Bird]

Are you sure it's a clutch or just a belt guide?

[samjmann]

Thanks Rare Bird,

Looking at your picture, there is just the motor, belt and sub-platter on the 128 MkII. Nothing else! So I thought the clutch must be in the motor. Bit of a 'anaorak moment' now..
There is actually two motors, one on top of the other on this turntable they are AC driven from a sinewave generator, the Ic's I changed formed part of this as well as the solenoid to operate the arm lift. The belt is a Thorens. Thanks again, SJM