Technics SL-1300 spinning too fast, Help!

Discussion in 'Turntables' started by jb4uc, Jan 21, 2006.

  1. jb4uc

    jb4uc New Member

    Thank you to anyone who can help me. The turntable just spins incredibly fast. I took off the bottom, no obvious problems inside. Everything appears to be pretty clean. Spent a lot of time poking and prodding, but to no avail.
  2. jblmar

    jblmar JBL & marantz

    Welcome jb4uc,
    Sorry to hear about your TT problem. The Technics models use ICs for speed control. I'll check with the people I buy semiconductors from. Where are you located? Do you have the schematic? You can PM me if you want the unit repaired.

  3. bully

    bully member

    It has a speed control (pitch control) on the front left side. How is it set? The light should be steady and in one spot as the table spins.
  4. jb4uc

    jb4uc New Member

    Thanks Bully & jblmar. I am located in Newtown, CT and do not have the schematics. The front left has a speed control (33 or 45), two pitch control knobs/dials (onr for 33; one for 45) and it doesn't seem to matter where any of this stuff is set. I have tried playing with these extensively. The strobe is functioning. I would be interested in having it repaired, this is a really nice TT!
  5. jblmar

    jblmar JBL & marantz

    Could also be the speed control (33 & 45 RPM0. If the switch is defective, the speed will run.

  6. jbpollock

    jbpollock AK Subscriber

    I think that the speed control levers on the top are for fine tuning. There are also a set of controls under the platter for more coarse control, if i remember correctly.
  7. jblmar

    jblmar JBL & marantz

    Check the table with a 45 RPM disc, How's the speed? If it's still off, the servo section needs to be checked. The 1300 is a DC Servo model. The 1301 is a Quartz DC Servo TT.

  8. jb4uc

    jb4uc New Member

    Thanks. I'll check the 33/45 switch. I have already played extensively with the coarse tuning controls under the platter, as well as the fine tuning controls on the top. The speed is unmeasurable, it spins so fast. Appreciate your help!
  9. jb4uc

    jb4uc New Member

    I checked the 33/45 switch for open/closed on each setting with an ohm meter. Seems to be functioning based on those tests.
  10. pinobot

    pinobot New Member

  11. tech_freak

    tech_freak New Member

    Turntable spinning too fast?

    Hi, Were you ever able to fix the problem? I just got a Technics SL-7 and I have the same problem. Any help would deeply be appreciated.

    Fellow Audiophile
  12. Rybeam

    Rybeam New Member

    Correct voltage ?
  13. dr*audio

    dr*audio Fish fingers and custard!

    The first thing to do is clean the speed change switches and the speed control with a contact cleaner. If that doesn't work, it will require troubleshooting. We need to know at this point whether it's a MkII or not. The Mark II is crystal controlled.
    In both cases the turntable has a sensor to sense the speed, and a reference to compare the speed to. If it's too slow, the control circuit applies a correcting voltage to speed the motor up. If Jblmar is correct, the DC servo type has a circuit that converts the speed sensor signal to a DC voltage that varies with speed. Let's say that it produces a DC voltage that rises when the speed gets higher. If you were to lose the speed signal entirely, or there was a problem in the frequency to voltage converter where the DC voltage it put out was too low, then the turntable would turn very fast as it does.
    In a crystal controlled circuit, there is a crystal reference oscillator and the speed sensor creates a signal that is compared with the reference frequency. The same faults apply here, too. If you lose the speed sensing signal, the motor will turn too fast.
  14. Fred Longworth

    Fred Longworth audio fanatic

    I have repaired a large number of Technics and Sony direct-drive turntables with runaway speed like yours.

    In many cases, the failure was caused by lack of feedback. If you look closely at the motor, you will see drive coils and feedback elements. Depending on the model, the feedback is acquired either via a tape head type device or via laminated inductors acting as pickup coils.

    It was the laminated inductors that caused the problem. Either due to living in an environment with salt air (causing corrosion) or because of a fluid spill, the laminated inductor had opened up, eliminating the feedback.

    The motor control IC, not receiving any feedback, dumbly thought, "Gosh, maybe if I go a little faster, I'll get some feedback." After going faster and still not getting any feedback, the IC even more stupidly thought, "Gee, maybe if I go even faster than that, I'll get some feedback."

    And so on and so on . . . until the motor was racing at about 120 rpm!

    In every case, I found the open connection and jumpered it -- and the problem was fixed.

    Fred Longworth
  15. analog addict

    analog addict Glory or Death!

    Mine hasn't exhibited this behavior yet...

    But it make me feel better there are folks around a place like AK who know how to take care of our problem children...Thank you Sir...You are a gentleman and a scholar...I always find your posts illuminating :D
  16. tech_freak

    tech_freak New Member

    Platter running too fast

    Hi Fred Longworth,

    Thanks for your insight. I have a SL-7. Could you guide how to troubleshoot and where I need to look for loose connection and sorder a jumper of some sort? I appreciate all your help. Thanks.
  17. Fred Longworth

    Fred Longworth audio fanatic

    The SL-7 is more of a challenge because disassembly is more difficult.

    The details that apply to the SL-1300 also apply to the SL-7. Note that on the SL-7 the lateral motion control belt for the linear arm is the #1 failure.

    Fred Longworth
  18. tech_freak

    tech_freak New Member

    SL-7 Turntable spinning too fast

    Hi Fred,

    I was able to disassemble it without any problems. Not to brag or anything I did lot of circuit works and quite comfortable doing soldering and de-soldering myself. Just not sure what to fix and/or look for. I Checked the tonearm belts. I don't think it has any problems. I could turn the power off and manually move the tonearm toward the center and power it up and the motor automatically moved it back to the original starting position. However, when I try to play a record, the platter start spinning really fast and the tonearm just sits there in its original position and does not move at all.

    Is there a way I could troubleshoot something for missing signal or something? Please help!
  19. Fred Longworth

    Fred Longworth audio fanatic

    It is unusual for the tonearm lateral motion belt to still be good. Also, the sliderails often get sticky.

    That aside, take a good look at the direct drive motor assembly, which comes as a module. Identify the feedback elements, which are either pickup coils, laminated coils or Hall-effect devices. Don't have the manual handy, so I can't remember which. These are on top, right under the donut-shaped magnet assembly, which is attached to the bottom of the platter. Don't confuse them with the drive coils, which turn the platter. The failure mode is an open connection associated with the feedback elements.

    Let me know if you find anything. A low-voltage ohmmeter is often useful in this investigation.

    Fred Longworth
  20. dr*audio

    dr*audio Fish fingers and custard!

    If the feedback is a coil, it will look like a zig-zag pattern on the printed circuit board. If it's Hall -effect sensors, they are small 3 or 4 lead devices with black plastic cases, arranged around the perimeter of the motor board, below where the magnet sits.

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