• The move to the new server is done. There are some software and database maintenance updates in process. This has us passing the hat around to help out. We appreciate any donations. Seriously, even a dollar helps. The payment page may be found here - https://www.audiokarma.org/support.html

Thorens TD 125 Barn Find

Rob_Feature

Rob_Feature

Rob Feature
Scored a Thorens for 20 bucks! Unfortunately it needs alot of love...My skills are average, but I figured I'd give it a go.

First problem: I fire it up and the speed selector only spins the motor (barely) when it's at a position right between 33 and 45. I cleaned those contacts with no improvement. Thinking either the motor is gunked up (feels kinda like it) or those ancient looking caps on the board need a swap.

Thoughts on getting this motor spinning again?

IMG_7304.JPG
 
Register to hide this ad
Rob_Feature said:
I fire it up and the speed selector only spins the motor (barely) when it's at a position right between 33 and 45
Click to expand...
Do you get a nice 'click' sound when the speed slide is switched to either of the speeds? This sounds like a mechanical issue to me, as if the connector arm between the slide switch and PCB had come loose or the PCB isn't fastened to the chassis with the two on board screws. As per the motor barely spinning, you need to measure the voltage to each of the motor windings for each of the speeds and adjust to 3.2V/5V/6V (AC) for 16/33/45 respectively. The exact procedure is in the Mk-II service manual. A recap is a viable option, especially of the two large power supply capacitors, but you need to know the general health status with the voltage first.
 
Thanks Tom....The slide switch is functioning mechanically how it should. I've accessed the board so I can see that the contact appear to be sliding correctly, no problem there. The board is securely fastened and everything seems OK in terms of the actual hardware functionality.

I feel like the connections are working as they should, but there's just no power being provided when the switches are in different positions...or there's power provided to the motor but it won't turn easily due to...well, something.

I recognize this is a pretty high end turntable and I'd love to get it working, but I'm trying to determine what it's going to take. I know it sounds crazy, but I don't know if I'm willing to drop a few hundred dollars into getting it spinning (I have too many other TTs already). So I'm trying to figure out if this is something fairly simple I can cleanup (ie. a recap, or cleaning connections/motor) or whether we're talking about taking it to a shop for an overhaul.

I don't think I have the know how to test the voltage, but maybe I can read up on that next. I'm wondering if those caps provide the power that would spin the motor...if those are dead, is my symptom a reasonable result? I figure a re-cap would be a first step because I know I can do it and it wouldn't be too costly.
 
I can probably walk you through this if you got a DMM and you can solder/desolder. I'd need some hi-res pics of the speed control PCB first though, good enough to spot trace cracks on the conductor side and burn marks on the components side.
 
Super kind of you, thanks Tom. My impression was that the PCB was really clean when I looked at it, but when I'm able, I'll go ahead and pull it out and shoot some pics to post here. I really appreciate your willingness to help, I'd really love to get this running if possible!

(oh, and yeah, got a multimeter and I'm decent enough at soldering PCBs...)
 
tnsilver said:
I can probably walk you through this if you got a DMM and you can solder/desolder. I'd need some hi-res pics of the speed control PCB first though, good enough to spot trace cracks on the conductor side and burn marks on the components side.
Click to expand...


:thumbsup:
 
OK, I've got this initial sketch for you:

xwWHyJM.jpg


It goes like this... Hook up your DMM (set to voltage AC) like in the picture to measure voltage to the two motor windings which are either the red and common or blue and common points.
Point "rt" (red) is the red lead to the motor, point "bl" (blue) in the blue lead to the motor and point "ge" is common to both. The principal is to set the exact same voltage on the red side, as on the blue side (which represent the two winding of the motor), Each voltage is set for the respective speed and each speed has two trimpots (corresponding to each side, red or blue). Once the voltages are set, we adjust the strobe knurled wheel variable resistor in the middle of the slide and use the the "F" trimmers to adjust the strobe as steady as possible. Then we check the voltages on each side again and adjust if necessary. The strobe adjustment will throw the voltage off a bit, so readjustment is routine.

  1. Start with the speed selector at 45 RPM and use the A1-45 trimmer to set the voltage to exactly 6V(AC). It requires very gentle, baby step moves on the trimmer.
  2. Once at 6V(AC) for 45 RPM, set the speed selector to 33.3RPM and use the A1-33 trimmer to set the voltage to exactly 5V(AC). Tiny steps, as before
  3. Once at 5V(AC) for 33.3 RPM, set the speed selector to 16RPM and use the A1-16 trimmer to set the voltage to exactly 3.2V(AC). Tiny steps again.

    At this stage you got the red side adjusted. Now do the blue side. Move the DMM red (positive) probe to point "bl" and set the speed slide to 45 RPM.

  4. Use the A2-45 trimmer to set the voltage to exactly 6V(AC)
  5. Once at 6V(AC) for 45 RPM, set the speed selector to 33.3RPM and use the A2-33 trimmer to set the voltage to exactly 5V(AC)
  6. Once at 5V(AC) for 33.3 RPM, set the speed selector to 16RPM and use the A2-16 trimmer to set the voltage to exactly 3.2V(AC)

    The final stage is making sure the strobe is right on spot and we use the "F" series of trimmers to set it up to snuff. It requires a visual check in the strobe window.

  7. Use the F-45 trimmer to set the strobe at 45RPM - make sure to look at the correct strobe band (upper)
  8. Use the F-33 trimmer to set the strobe at 33RPM - make sure to look at the correct strobe band (lower)
  9. Use the F-16 trimmer to set the strobe at 16RPM - make sure to look at the correct strobe band (lower)

    Now, here's the bummer part: Any correction to the strobe "F" series of trimmers (for the strobe adjustment), will throw off the voltages of A1-XX and A2-XX by a bit. You need to go through all the steps again and refine the adjustment in a loop. It's time consuming and quite a PITA and it helps a lot if you have two DMMs to hook up to "rt" and "bl" and share a common "ge". This way you can compensate for the red and blue side simultaneously and save a lot of time.

If you cannot pass stage one (45RPM and 6V using the A1-45 trimmer) or it gives you erratic results, it's likely you need to recap the 2 electrolytic power supply capacitors (1000µF/25V).
I used a pair of Nichicon TVX series caps (pn TVX1H102MCD) after that, you should be able to dial in the voltages.
 
Wowza. HUGE Thanks for this Tom!!! Looks like my weekend is now booked! :) I don't know if I can follow all this but I'll sure try.
 
Rob_Feature said:
Wowza. HUGE Thanks for this Tom!!! Looks like my weekend is now booked! :) I don't know if I can follow all this but I'll sure try.
Click to expand...

Like the Hitchhiker's Guide to the Universe days, Don't Panic! The process is relatively easy, it just looks intimidating when all written out that way. It is essentially putting a meter on the correct two points and adjusting a control, rinse and repeat. Far less complex a process then it looks when written out. Be patient, take your time and you should be able to get through it just fine.

If you decide not to bring it back to life (and I strongly encourage you to do just that), let me know. I might be able to help, and if you decide to move the table down the road, I might be willing to buy it from you.

Shelly_D
 
First, lemme say "thanks" for the confidence boost Shelly. Once I sat down and really looked at Toms steps, i realized he did a great job OVER explaining (which is absolutely appreciated), making it look a little complicated. But it's quite simple, really.

So, I think after diving in I'm going to need to change those caps first. My first test either got me 0v AC or a number just jumping all over (from 7v to 0v). So I think ordering up those caps is on the agenda now. I'll report back one I've got those replaced! Thanks everyone!
 
Rob_Feature said:
My first test either got me 0v AC or a number just jumping all over (from 7v to 0v).
Click to expand...
could be a problem but you may want to deoxit the old trimmers and make sure to use good clip-on probes in good shape for a reliable contact during the procedure.
Rob_Feature said:
is there a reason you got the 50v instead of 25v version?
Click to expand...
Probably couldn't find 25V/1000uF axial caps at the time. Can sure find them now though...
Rob_Feature said:
I always hate to pay shipping on just a couple caps. Should I replace the other 9 caps on the board as well? Or just leave those alone?
Click to expand...
Aha! I can make the shipping worthwhile with a nearly complete BOM for the TD-125 Mk-II, but there's really no reason to shotgun good parts. Those olive/khaki Thorens film caps rarely go bad.

4eK9GRG.png


...and if you wanna do the improved op-amps mod, red goes out, green comes in:

Ka3Vgwy.jpg
 
Thanks Tom, all great input here . I'm gonna order those 25v and leave the others in place if they tend to be reliable. Will get that ordered and should have them about mid-next week...will report back then. Thanks for going above and beyond to help!
 
Rob_Feature said:
Tom, is there a reason you got the 50v instead of 25v version?

And, I always hate to pay shipping on just a couple caps. Should I replace the other 9 caps on the board as well? Or just leave those alone?
Click to expand...
Digikey doesn't charge shipping...if you send em a check for the price of the parts with local tax. I use that for small orders at times. Check out their terms and conditions.

I rebuilt a 125 II per Tom's build sheet including new chips. After speed adjustments everything worked like new. I'd continue to put more crap in this thread but you are in good hands with Tom handling the Q&A. Anything I add would be just another BS comment. See what I did there?
 
Whelp, got the caps, put 'em in. No change. No matter how I try to measure, the voltages are either 0 or are popping around. Once in a great while I'll get what looks like a legit measurement...then it'll go away. I also get something that looks legit when I ONLY put the ground probe on the ground pin...I know that makes no sense, but only mention it because it seems odd (and may give a clue). I touched up the pins for red/blue/ground just in case they weren't solid, but that didn't seem to help at all.

Not sure where to go next. Here's a pic of the board so you can see if you see any problems that I don't. Thanks for the help thus far!!

IMG_7377.JPG IMG_7378.JPG IMG_7379.JPG
 
Not sure where to direct you with this. The circuit, if I understand it correctly, is two tunable oscillators producing their sine waves 90 degrees out of phase with each other. Not having serviced this before I would be checking each section of the circuit with Volt meter and oscilloscope looking for stable DC power for the op-amp circuits and driver transistors and DC free sine waves out of the output pins on the op amps. I am assuming that you don't have an oscilloscope. If all else fails, you might be able to find another AK member near you with either the equipment, experience or both to help you. What part of the country are you in?

Shelly_D
 
Hard to tell by the pics but a lot of the solder joints (power supply caps, one of the op-amps, bridge rectifier, connections from the power transformer plus more) appear to be scorched as if made with a too powerful soldering iron.
The traces on this board are fragile and easily damaged. It may be just a shadow or an optical illusion on some, but many look suspicious. In any case, I can't tell if the op-amp with what looks like soldering scorch marks is heat
damaged or it's just a soldering issue. I'd get a 15 watts (tops) soldering iron and rework all those suspicious solder pads, then verify them for connectivity with a DMM. Can you please release the PCB mount screws, carefully
(without breaking any of the leads) flip it over, and take some good pix of the components side? What AC voltage are you getting out of the transformer?


3NTCre7.jpg
 
Thanks Tom, I wondered the same thing about those solder points...they looked "dirty" at first, but then the more I looked they did look a little burnt. My first though was that someone tried to repair this previously and failed (maybe that's why I ended up with it so cheap)....I'll touch some of those points to ensure a good connection, will measure the AC from the transformer, and post some pics soon. Thanks for the input!
 
Started looking at this again today and (It took me this long to realize) it's pretty much covered in a thin layer of really sticky stuff. It seems related to the dark solder marks (which aren't burnt, just brown and gooey looking)...I have a feeling someone soldered this with flux and it was spread all over the place? Thinking maybe that would account for random measurements too if the goo was interfering with measuring the currents (?)
 
If those traces really are burnt I would take the time with my schematic to measure out the signal path and see if you have opens. This can be tricky since intermittents too can be a royal pain to find, possibly hidden my solder mask. Get those boards cleaned of flux or whatever it is then do a close physical inspection through magnification.
 
You must log in or register to reply here.
Back
Top Bottom