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TD-125 playing up

M

matt j

pfm Member
Recently this has started getting worse, but it has done this for as long as I've owned it and all the various suggestions haven't cured it.

On switching off the belt drops down the motor pulley and rides on the tapered part of the pulley, so that on next start-up it can take a while to either jump up on it's own or manually spinning the platter before start up sometimes solves it but recently even that has stopped working.

It's getting annoying now hence asking here, I've cleaned and adjusted various bits to no avail.

Here is a short video to explain, although this video is a little while old and now it doesn't jump up on it's own for ages.

 
what is the pulley made off. cant you slightly rough the surface with light emery /glass paper to get alittle more grip
 
I don’t know much at all about the TD-125 other than I’ve always liked them when I've heard them, but I have a feeling that behaviour is deliberate. If you look at the shape of the pulley there is no reason I can think of for it to be tapered/rounded like that unless the intent is to have a ‘slow start’ where the motor has a slightly easier task of getting the heavy platter up to speed by effectively starting at a lower gearing (i.e. smaller diameter pulley). At that point in time Thorens knew exactly what they were doing and all aspects of the design would have been very carefully thought out. I suspect it is doing what it is intended to do, though giving everything a damn good clean wouldn’t hurt!
 
You need to trim the angle of the motor using the motor mounting screw nearest the platter. That screw is spring mounted. Trim until the belt runs nice and centrally on the fattest part of the pulley.

A new belt may be needed too.
 
I suspect your motor is weak for some reason, or there is some unwanted friction somewhere. I think the TD125 has some sort of electronic motor drive/speed change, so plenty of opportunity for minor faults.
 
The stepped nylon pulley has a spring loaded slip clutch mechanism. These can be partially disassembled and tightened by first pushing the upper larger diameter segment* downward to reveal a recessed hex head set screw within the side of the metal bushing. The coil spring that sits beneath can be removed, stretched slightly and replaced; essentially restoring the clutch to as new performance.

* On the mechanical speed change Thorens models, this is the 45rpm segment, with the smaller diameter lower segment being for 33 1/3rpm. Electronic models run the belt on the top segment only and adjust the motor rpm accordingly.
 
Tony L said:
I don’t know much at all about the TD-125 other than I’ve always liked them when I've heard them, but I have a feeling that behaviour is deliberate. If you look at the shape of the pulley there is no reason I can think of for it to be tapered/rounded like that unless the intent is to have a ‘slow start’ where the motor has a slightly easier task of getting the heavy platter up to speed by effectively starting at a lower gearing (i.e. smaller diameter pulley). At that point in time Thorens knew exactly what they were doing and all aspects of the design would have been very carefully thought out. I suspect it is doing what it is intended to do, though giving everything a damn good clean wouldn’t hurt!
Click to expand...

Not sure Tony, but now it doesn't jump up at all so I doubt it's supposed to be that way.

Mike P said:
You need to trim the angle of the motor using the motor mounting screw nearest the platter. That screw is spring mounted. Trim until the belt runs nice and centrally on the fattest part of the pulley.

A new belt may be needed too.
Click to expand...

It has a new belt and all has been cleaned etc. and I've tried adjusting the trim screw without joy, although I'm not sure that is the issue anyway because when it does run properly the belt is bang on the correct part of the pulley and everything runs inline, it's just at switch off it drops off.

Craig B said:
The stepped nylon pulley has a spring loaded slip clutch mechanism. These can be partially disassembled and tightened by first pushing the upper larger diameter segment* downward to reveal a recessed hex head set screw within the side of the metal bushing. The coil spring that sits beneath can be removed, stretched slightly and replaced; essentially restoring the clutch to as new performance.

* On the mechanical speed change Thorens models, this is the 45rpm segment, with the smaller diameter lower segment being for 33 1/3rpm. Electronic models run the belt on the top segment only and adjust the motor rpm accordingly.
Click to expand...

Thanks, this sounds like the next thing to look into. will report back.
 
matt j said:
Not sure Tony, but now it doesn't jump up at all so I doubt it's supposed to be that way.
Click to expand...

I’m likely wrong as I don’t know the turntable at all, and I certainly didn’t realise it had a clutch system, though I remain curious why the pulley is that shape. Anyone know? The LP12 has a vaguely similar contour to the pulley and again the belt tends to start low and swiftly climb. My assumption was it was some kind of gear mechanism to aid a fairly weak motor in starting up a heavy mass.
 
See my addendum marked with an asterisk in post #6 above.

I suspect that Thorens decided to stick with the existing 2-speed pulley with slip clutch mechanism for smoother startups, as they had one developed for the mechanical speed change decks already.

With the introduction of TD126 'Electronic' Thorens finally got round to making a single diameter/running surface variant of their slip clutch pulley which continued in revised form into the TD3xx series...

TD126 Drive Pulley:
IMGTD126_0439_%285%29.JPG



TD316 Drive Pulley:
bild-2_62896.jpg
 
Any ideas as to which way to alter the spring? I've stretched it slightly but it was already under a decent amount of compression when I took it off. It's not made much difference.
 
With reference to Mike's suggestion above, try adjusting the motor azimuth slightly more toward the platter, i.e. tilting away causes the belt to ride down, whereas, tilting toward causes it to ride up.
 
Likely so, in which case my last suggestion will only make things worse, unfortunately.

EDIT: Analogseduction.net are offering genuine Thorens belts.
 
I've played with the azimuth a fair bit to no avail.

I may try another new belt then, although this was a genuine new Thorens belt when I bought the TT last year.
 
I think you're right in that it could be the belt. I gave everything another clean up and it was a bit better, I then put a half twist in the belt so as to shorten it a little and it's now staying in the right place when switching off.

I may leave it like this and see how it goes as those belts aren't cheap and this one isn't that old.
 
Great idea!

I was just now popping in to suggest re-cleaning the belt and pulley and putting the belt back on 'inside out'.

I missed your post re which way to alter the spring yesterday. Basically, if it takes a good pinch of the pulley to stop it from rotating with the motor on then the spring tension is fine.
 
RE: clutch spring tension- I think it's fine then, in that case.

Not sure why the belt hasn't lasted very long.
 
I've seen belts expand very prematurely if they've been contaminated with oil.

Just a couple of weeks ago I fixed a TD166 for someone which had similar issues. He'd replaced the belt already but had contaminated the new belt with oil causing it to swell/stretch and become slack (overfilled main bearing and got oil everywhere). A thorough degrease of all surfaces and another new belt had it running sweetly again.
 
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