Thorens TD125 MKII Motor Issues

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1935Pontiac
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Thorens TD125 MKII Motor Issues

Post by 1935Pontiac » 22 Feb 2018 06:50

Hello
A year ago I was given a Thorens TD125 mkii turntable by a friend. When plugged in the neon strobe light illuminated but nothing happened with the motor.
Reading one of the other posts, I found that the two 1000uF capacitors (I think labelled C2 and C4 on the schematic) could be problematic. I replaced these and resoldered a loose wire, and now the motor will twitch when first turned on, and when the speed is changed. If you hold it partially between the speeds, the motor turns, but slowly, but on each speed setting it only vibrates. I thought that the issue would then be the speed selector switch, so I dismantled it and cleaned the contacts, it now makes better contact but the same issue persists.
I’ve also cleaned the minor speed adjustment switch as well as the variable resistors (I think) on the underside of the circuit board. I’m not super knowledgeable on these things, and have relied predominantly on this website for assistance, I’m 17 and only have basic soldering skills.
The motor is a sealed unit, but seems to turn freely enough: are there any other issues anyone can think of that might be causing this, or may I need a new motor, alternatively, how can I test if the motor is receiving the correct voltage etc.?
Thanks in advance,
Ben Creemers

medwaybeat
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Re: Thorens TD125 MKII Motor Issues

Post by medwaybeat » 22 Feb 2018 08:40

Buy a cheap multi-meter. You can then check you are getting volts to the motor and check the resistance of the motor. I doubt the motor is at fault.

1935Pontiac
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Re: Thorens TD125 MKII Motor Issues

Post by 1935Pontiac » 22 Feb 2018 08:41

What voltage/resistance should the motor be and which of the four leads do I test? (Two black, one blue, one red)

medwaybeat
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Re: Thorens TD125 MKII Motor Issues

Post by medwaybeat » 23 Feb 2018 08:25

I think the motor on the TD125 is 110v.
I have a TD150 and got 100v black to blue and 90v black to red.
There was no resistance across blk & blu or blk & red they all came up as open circuit.

Jacques51
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Re: Thorens TD125 MKII Motor Issues

Post by Jacques51 » 23 Feb 2018 13:04

All,

The motor on a TD125 gets it's voltages (and current) from a generator, a Wien bridge oscillator. It's on the board where you replaced the 1000 µF capacitors.
The voltages are around 3.2 - 6 volt, IINM. Dowload the service manual from the library here on VinylEngine. Page 3 lists the electronic adjustment. Not a straightforward thing, but with some patience and maybe a re-try or two, it should be possible. You'll need a decent voltmeter, maybe one you can borrow.

Sometimes adjustment potmeters have gone faulty and there can be many other reasons why the motor isn't getting the right voltage or phase shifts. If it turns now and then, even at an incorrect speed, then it's probably not faulty.

Success!

Jacques

1935Pontiac
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Re: Thorens TD125 MKII Motor Issues

Post by 1935Pontiac » 26 Feb 2018 08:50

Firstly, thank you for all of your help :-)
Okay, the motor is definitely working, I was able to adjust the phase 2 potentiometers to the correct voltages (A245, A233, and A216, to 6V, 5V, and 3.2V respectively). However, the Phase 1 potentiometers can only be adjusted to a maximum voltage of 2.3V for A145, 2.2V for A133, and 1.8V for A116. The motor will work when the Phase 1 potentiometers are adjusted to their maximum, however will often twitch for a few seconds before turning in the correct direction.
Any ideas?
Thanks,
Ben Creemers

waj4all
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Re: Thorens TD125 MKII Motor Issues

Post by waj4all » 11 Mar 2018 11:28

Nothing wrong with your motor. It's fine, I'm sure - so rest assured on that score.

Replaced the two large caps in my own 125 too - just as you did. A precautionary measure, in my instance. However, subsequent to that, my motor cut out once and only returned to normal when I slid the speed-switch a few times. So, in my case, I guess it's pretty obvious that I should clean said contacts if the issue ever returns (though I'm reluctant to upset the present state-of-tune just for that if the issue continues to stay away).

Your issue seems a bit more 'advanced,' however, and so I'll link you to a thread I'd found in my own research, as I believe the solution to your problem could be in there somewhere (or in links there-from) especially where the replacement of trannies and ICs are examined late in the thread. Refer to: http://audiokarma.org/forums/index.php? ... ng.348375/

Hope this helps.

Best of luck.

dlove968
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Re: Thorens TD125 MKII Motor Issues

Post by dlove968 » 18 Jan 2020 17:18

My sincere thanks to the many contributors, who showed me the way to get my TD125 MKII running again.
I bought my turntable new in 1974, along with an SME 3009 S2 Improved arm and Shure V15III. I was a subscriber to Audio and Stereo Review magazines in those days, and attended the Washington (DC) HiFi Show every year. You could spend more than I did, but the consensus seemed to agree that the setup I chose was excellent. I used that equipment regularly for the next 30 years with zero problems. In 2005 I packed up and moved to a new town. When I set up my stereo system, the TD125 didn't work. The neon strobe bulb lit up, but the motor did not do anything. I had been building a collection of CDs, and carrying an iPod (I was now traveling constantly for my job), so the lack of a way to play my records (about 700 in my collection) wasn't a serious concern.
Well, now I am retired, and have time to work on projects. And I have some teenage grandkids who are interested in "vinyl." So it was time to get the TD125 going again. I was an electronics technician early in my career, so replacing components on the circuit board would be no problem. I have no test equipment other than a multimeter, so I decided to start by replacing only the 1000 uF electrolytic capacitors. One was shorted, but the other passed the limited test I could do with the multimeter. I installed two new ones. Success! I had no difficulties setting the motor speed voltages per the service manual procedure, so I concluded that none of the other components require changing at this time. I devoted a couple of hours to cleaning and verifying the tone arm settings, and am now enjoying listening to LPs again!
I am astonished that the belt appears to be satisfactory. A close examination shows no drying or cracking, and I can't detect any slipping. I will buy a new one anyway, but this must surely be some kind of longevity record.

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