Thorens TD147 auto stop not working

Really glad you figured that out! It never ceases to amaze me, all the little idiosyncrasies these Thorens tables have. They're maddening but worth it in the end.
 
Dennis Gardner said:
Good bit of info to know! It sounds like it may have a weak return spring.
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From looking at the parts shown in the service manual, there doesn't appear to be a spring available that would serve to bring the lever back to the correct position. There is a little tension spring - 4 320 024 - that is connected to the "detent lever" - 6 862 018 - but it doesn't seem to have anything to do with returning the lever to any position at all.

What is odd is that the tone arm on my TD 147 works fine in the 45rpm position if I manually pull the lever down a bit after it starts, but not all the way to shut off the TT. But it does not work the same in the 33.33rpm position. As much as I've examined the switching mechanism to determine what is different in the two speed positions, I cannot find anything materially different. So frustrating! :dunno:
 
UPDATE: The little spring 4 320 024 appears to have everything to do with returning the lever. My Bad. The problem with my 147, however, was that the "rastscheibe" (6 862 001 or mounting disc per Google translate) was not moving freely within the mounting block (6 862 000). Removing the disc from the block was very difficult due to the use of the starlock washer (8 599 010) on the disc's shaft. I finally got it off, only mangled a little bit, and was able to separate the disc from the block with a bit of effort. I could see no reason for the fitting to be so tight, so I sanded the shaft down with 120>350>1000 grit sandpaper until it moved freely within the block. I even added a bit of sewing machine oil to the shaft. After re-assembly, the speed control knob returned easily to its stopping position after being released from the motor turn-on position.

The tonearm lift at the end of the record now worked in the 33.33rpm position as well as at the 45rpm setting - most of the time! But not always... :confused: I found that if I let the lever snap back to it's resting position, it usually worked. But if I just released it gently, it did not perform as designed. Still more investigation needed! :rolleyes:
 
UPDATE #2: I followed all the instructions for setting the auto-stop adjustments as per the service manual. The shutter was adjusted about 1mm closer to the drill bit but it didn't make a bit of difference to my voltage readings (pun intended!). Speaking of which, what I am measuring at TP3 is WAY different from what the manual specifies. Instead of measuring between 4.5 and 4.9V at TP3 when the shutter is fully engaged, I measure 7.75V. When the optical path is opened completely, e.g. the shutter is move completely away from the LED as if the tonearm had reached the center of the disc, the voltage goes UP to 8.19V instead of down to .5V as specified in the manual.

The manual says to use trimmer R102 to make adjustments to the voltage levels to arrive at the specified voltages but mine are so far off I'm wondering if I should even attempt to adjust R102. It has a drop of Loctite on it that apparently hasn't changed position since manufacture, so I'm hesitant to mess with it.

What do y'all think?

Pat
ps. The auto stop continues to work perfectly at 45rpm but intermittently at 33.3rpm.
 
UPDATE #3:
After following all the instructions for setting the physical tonearm lift/auto stop adjustments as per the service manual, I used a variac to reduce my 121VAC house voltage so that the output of the Thorens 16V supply was exactly 16VAC to the electronics. With that precise 16VAC initial voltage, I get 14.75VAC at both TP1 and TP6 with the motor off. The SM says I should get 21V at TP1 with the motor off. With the motor on, I measure 8.53VAC at TP1 and 8.48VAC at TP6. The manual says I should be getting 16VAC at TP1 with the motor running. I measure 4.36VDC across the Zener Diode D108 with the motor on. So my voltage readings for both TP1 and TP 3 seem to be way off.

In this YT video, (
) a guy indicates he fixed the auto-shut off problem on a TD146 (same Service manual as 147) by replacing a 47nF capacitor that sits across the on/off switch contacts. Do you think that would resolve my voltage disparities? That capacitor does not show up anywhere in the Service Manual, btw.

Any and all suggestions welcome!
 
The Judge said:
Are you measuring AC or DC volts at the test points?
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Thanks for the question, @The Judge. I was measuring DC volts at the test points. But after endlessly fiddling with the shutter, I finally got it into a location that works 95% of the time. I have no idea if the electronics have any real effect on whether the arm lifts or not - and nobody has been able to tell me - but I'm OK with it lifting 95% of the time at this point. Thanks again for you question but it's up for sale at this point!
Cheers,
Pat
 
sportsmaster said:
Alright I have gotten the auto stop to work! I learned a lot of things since I started this thread. Mainly, I learned that the auto stop doesn't work if you leave the knob in the "start" position. You have to turn it to point at 33 or 45 once the motor starts running. I didn't see this in the manual anywhere and had to learn it on my own which took forever. But I'm relieved I finally got it to work.

Secondly, I learned that the LED used here is actually an infrared, so that's why I couldn't see it. But with a cell phone camera, you can take a photo of the light. It's a purple color, pretty cool. I guess this one is around 950nm frequency at its highest intensity which is right where the optical sensor is most sensitive. I would not have expected this kind of technology from 1970s


View attachment 799247


Also I solved a problem with the RCA cables. I wanted to install jacks, but I did not want to drill holes in the nice Thorens plinth. So I decided to buy one of those headphone jack to female RCA cables. I cut off the headphone jack and soldered each female RCA cable to the turntable. You can see in the photos they are just hanging out the hole in the case where the original cables came out. It's easy to plug and unplug the RCA cables, and I didn't have to ruin the nice veneer on the original Thorens plinth

View attachment 799248 View attachment 799249

And one last point. While I had the table upside down, I put a few drops of singer sewing machine oil on the motor, right on the spindle. It took about half an hour with the motor running for all the oil to seep in, but the motor is now a lot quieter.
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Thanks for under the chassis of the circuit board, the one I am fixing for friend half the board was broke to the left of the spring and the board was mounted to the under side of the bottom cover with wood screws...People's work just amazes me!!! This thing has sat in a basement for 20+ years and I did lower the variac to get the 16VAC, but should of put an inline fuse on the one side of the AC input. I fired it up the motor ran. I shut it off to start measuring voltages and smoke and 2 traces burned off. It took out the 4 diodes in the power supply, and the one 470uf cap reads way high and has high ESR, maybe that was the culprit. So far every other part tests ok. Not sure if the 2 IC's got hit. At least I have solved the mystery. Now to test it again...
 
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