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Motor wiring on TD-125 MkI question

Discussion in 'Turntables' started by gkargreen, Jun 7, 2018.

  1. gkargreen

    gkargreen Active Member

    Messages:
    459
    Location:
    Fairfax, VA
    working this up, cleaning, etc. and my blue wire broke off the pcb. I did not note which terminal it was connected to before it broke off, and cleaning each terminal in hopes of finding a piece of the wire did not work either. These damn boards seem to change with each one, I have looked at dozens of these board on google and each one is different, none quite matching mine. The only thing I have to go one is the board is marked blue wire, but there is also a brown wire coming from a transformer going to that same terminal and, as noted above, I did nt find any piece of broken wire. Any ideas? Thanks
     

     

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  2. tnsilver

    tnsilver AK Subscriber Subscriber

    Messages:
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    The German color codes are printed on the silkscreen on the conductor side of the PCB, but
    can get blurry or even wiped off:

    [​IMG]
     
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  3. gkargreen

    gkargreen Active Member

    Messages:
    459
    Location:
    Fairfax, VA
    Thanks Tom, that look just like my board, wondering why I have a brown wire from the transformer hooked up where the blue wire goes, any idea?
     
  4. tnsilver

    tnsilver AK Subscriber Subscriber

    Messages:
    3,235
    Location:
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    dunno. maybe someone had been there before. Normally, the AC power supply lines from the
    transformer hook up to the rectifier bridges and not directly to the motor feed.

    [​IMG]

    [​IMG]
     
  5. Blue Shadow

    Blue Shadow I gotta get me a new title

    Messages:
    21,016
    Location:
    SE PA
    Time to think about where the wires start and end instead of color
     
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  6. gkargreen

    gkargreen Active Member

    Messages:
    459
    Location:
    Fairfax, VA
    Thanks, guess I need a schematic that sounds the wiring for my table. Tom, the schematic you show doesn't match my pcb, but the first pic looks just like my pcb with the caps and the single rectifier.
     

     

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  7. tnsilver

    tnsilver AK Subscriber Subscriber

    Messages:
    3,235
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    Ah... OK, the previous schematics is from the SM but I found out there's a newer revision of the Mk-I with just one rectifier bridge, like yours.
    On this revision, one of the transformer leads is soldered to the same terminal as the blue motor feed. It's originally a green/lime colored wire.

    [​IMG]

    [​IMG]

    Post a pic of your pcb, both sides please.

    What was the problem with your PCB/TT?
     
  8. gkargreen

    gkargreen Active Member

    Messages:
    459
    Location:
    Fairfax, VA
    Hi Tom, here are the pics to follow. There was no problem with the board, other than finding the values of the caps so I can restuff the board, as well as clean the adjustment pots. I think what happened was that the wire broke loose when I flipped the board over. So it appears that the brown wire is also attached to the middle/blue terminal on the pcb, from teh schematic that should be the center tap of the transformer, correct? I can measure that out to make sure. I appreciate all the help, and I am sure to need more as I bring this table up to full working order, I have a presentation at our radio/audio club meet and am trying to get the table ready for that, thanks!
     
  9. gkargreen

    gkargreen Active Member

    Messages:
    459
    Location:
    Fairfax, VA
    photos... DSCF6656.JPG DSCF6657.JPG DSCF6658.JPG the blue wire from the motor is just hidden by the board in these pics....
     
  10. tnsilver

    tnsilver AK Subscriber Subscriber

    Messages:
    3,235
    Location:
    Boston
    It appears so. I'm not familiar with this revision of the Mk-I. I just had a look at my spare Mk-I PS section and the transformer has 2 red and 2 brown wax/paraffin coated output power leads. The one in yours appears to have 2 reds and only one brown. It does looks like the blue wire detached from it's terminal where it was originally soldered with the brown wire. It appears somebody did some work on this board already (red film caps, maybe the 100V EC), and if there's no problem with the PCB, I'm sure you'll recap it with no issue. I'd use Deoxit D5 and then FaderLube on those silver contact tip wiper trimmers, no abrasives. Remember the voltage adjustment for the 3 speeds. It's in the German/French/English service manual. It's a wonderful turntable. Best of luck with it!
     
  11. gkargreen

    gkargreen Active Member

    Messages:
    459
    Location:
    Fairfax, VA
    Tom, want to thanks you for all your help! I do have a few more questions, what do you recommend for the grease/oil in the bearing well, the original looks like some kind of grease. Also, I did hook up the blue wire and turned the table on and it works fine, although the speed locks in with the control all the way to left/+ side. And while the table runs, the torque is pretty weak, doesn't take much to slow/stop the table from rotating, is this normal? Finally, the motor mounting screws, one of them had a spring mounted under it, is there some procedure to adjust the screw to orient the spindle in some fashion? Thanks again.
     

     

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  12. tnsilver

    tnsilver AK Subscriber Subscriber

    Messages:
    3,235
    Location:
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    No grease! It's not original and it's probably the reason, in addition to a stretched belt, your TT lacks torque. I use solely Singer sewing machine oil in all my 10mm Thorens bearings, but you got to clean the bearing well with IPA and polish the bearing shaft with metal polish first. While at it, put a drop of Singer on the motor shaft, underneath the pulley, and a drop on the motor shaft visible from the other end. Just a drop though.
    The service manual addresses this issue and I've referred to it as voltage adjustment. It's a calibration thing that must be done. It's in the manual but the essence of it is place the pitch control knurled wheel in the middle, measure AC voltage on the black and blue motor feeds and adjust voltages (8V/5V/2.5V) for each of the 3 speeds starting with 45 RPM. Then you need to trim out any DC voltage using another trimmer until it's 3-5mV tops.
    These are the three motor mounts screws that are used to adjust the motor shaft azimuth. The way it's done is to release all of them just enough for some leverage with the motor angle in relationship to the deck. Then, using only the screw with the spring (closest to the platter), the shaft and pulley are adjusted to be totally perpendicular to the deck. After that we can tighten up the screws (not necessarily all the way) without loosing the adjustment. The pulley must be totally aligned 90° for the belt to grab on properly.
     
  13. gkargreen

    gkargreen Active Member

    Messages:
    459
    Location:
    Fairfax, VA
    Thanks Tom! I am running these fixes down that you gave me, will let you know how they work out. One question I have is the three bolts that hold the top plate to the bottom plate, they have the little gray rubber washers on them, is there some amount of bolting together that I should do when reassembling them? Do I torque the nuts all the way down on those?
     
  14. gkargreen

    gkargreen Active Member

    Messages:
    459
    Location:
    Fairfax, VA
    Tom, do I need to have the turntable sitting in the operating position and with the platter running to measure the voltages? Thanks!
     
  15. gkargreen

    gkargreen Active Member

    Messages:
    459
    Location:
    Fairfax, VA
    oops, and making the pot adjustments?
     
  16. tnsilver

    tnsilver AK Subscriber Subscriber

    Messages:
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    Location:
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    Yup, and it's in the service manual. You need an AC/DC volt meter and some (very) basic knowledge in taking voltage measurements.
     

     

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  17. gkargreen

    gkargreen Active Member

    Messages:
    459
    Location:
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    No worries about the voltage measurements, I do a good bit of electronic restoration, haven't done many turntables though. The service manual I got of the 'net wasn't very clear or quite complete may need to get the one from here on AK...
     
  18. gkargreen

    gkargreen Active Member

    Messages:
    459
    Location:
    Fairfax, VA
    Hi Tom, have been working on this, got the new caps in and when I run the table I noticed a "dip" to the platter as it rotates. Later I saw a marking on the outer platter saying "low" but I notice a dip on the inner platter as it rotates. What clued me to this was a little wobble in the timing display (for want of a better word, the speed dots that are adjusted to be stationary by the speed control). Is this a "killer" for getting this table to operate correctly and/or to perform to its best performance level? Thanks, Randy
     
  19. Blue Shadow

    Blue Shadow I gotta get me a new title

    Messages:
    21,016
    Location:
    SE PA
    The dip on the inner platter could be a bent shaft. If that is the case a replacement inner platter sourced from the bay might make the table correct again. You need to look at the movement of the inner platter and verify if that is the case or if the bushing in the table is damaged. This part is replaceable on the early 125s.

    This issue needs more investigation otherwise Tom would not have used the dunno above.
     
  20. gkargreen

    gkargreen Active Member

    Messages:
    459
    Location:
    Fairfax, VA
    Thanks Tom & Blue, just got back in town and had a good look at the platter spinning and indeed there is a noticeable dip in the strobe when spinning, I confirmed that the inner platter, when spinning, does indeed slightly dip from a visual true looking at the edge of the inner platter, so a bent shaft may indeed be the issue. FWIW, if left in what affect to the sound would such a dip have on playback, a bit of "wow" perhaps? I am going to start looking into a new platter just in case.
     

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