SONY TC-55 - speed trouble...

Discussion in 'Tech talk' started by jacobsteel, Feb 12, 2022.

  1. jacobsteel

    jacobsteel New Member

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    Dear forum!

    I'm restoring av SONY TC-55, an early mono tape recorder. It's exceptionally well built, all metal, shiny brass and cast aluminum. Almost no plastic at all. It also hows several interesting similarities to the 10 year later TPS L2.

    So far I've put in new belts, everything is cleaned, polished and carefully lubricated. Fast forward and rewind works perfectly. Play works also, but the speed goes up and down a bit. All switches have been cleaned and there are no contact malfunctions.

    It does have a speed potentiometer (and presumably some regulation/governing) but I've yet to see a schematic. I've changed the old trim potentiometer to a new one but the problem persists. The motor feels strong and runs evenly (but I haven't been able to check RPM directly on the motor).

    Still, after 4-5 hours, I'm running out of ideas. Has anyone fixed this one? Or got a schematic? @Deb64 ?
     

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  2. Deb64

    Deb64 Active Member

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    Unfortunately I can't help as I don't have any experience with this model, or access to a schematic.
    There are one or two things I would check. Firstly, does the pinch roller rotate freely. It may be worth removing it and cleaning the steel pin and the hole in the centre of the pinch roller. If there is any grit or old grease in there, it could slow the pinch roller.
    Also, is the capstan shiny and smooth? If so, it could be slipping against the tape. It may be worth sanding the surface very lightly with a very fine grit wet and dry paper to put some texture on the surface.
    I would also check that the head is not pushing too far into the cassette and pinching the tape between the head and the pressure pad in the cassette.
    I hope this helps.
     
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  3. Arky Malarkey

    Arky Malarkey New Member

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    5C840DA1-4BAB-4DEA-BA53-BE5892CE9035.jpeg

    Great little machines, aren’t they? Built like a tank and weigh about as much. Picked these two beauties up on eBay some 15 years ago when they were still going for no more than five Euro’s a piece (those were the days).
    As far as the wobble goes: not a tech myself, but Deb64’s advice about the pinch roller makes sense. Here’s my own layman’s two cents worth: Are you sure it isn’t the cassette?
     
  4. Valentin

    Valentin Well-Known Member

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    @jacobsteel I agree with what @Deb64 pointed out. In my opinion, you need to find out if wobble is from the motor itself/electronics or from the mechanical side.
    It's more likely to be from the mechanical side, but the motor or driving electronics can't be completely ruled out (however, I would leave those last).

    There are many things that can cause high wow&flutter: old grease in the mechanism which makes pulleys hard to turn (including the pinch roller), an incorrect belt (cheap ones sold in 50pcs packs for example), a bad/worn motor, a hard pinch roller, a polished capstan (some already mentioned).
    In regard to the pinch roller, if you go to the trouble of removing it and taking the pin out just repalce it with a new one. From these pictures (https://www.petervis.com/Cassette_Tape_Recorders/tc-55/head.html) I assume it's the big 13 x 8 x 2mm one that is used.

    As for the speed trimpot, I would suggest putting the original one back as it's likely made of ceramic material (much lower temperature coefficient than the typical one). As a rule of thumb, that trimpot is only suspect if battery acid or capacitor electrolyte has leaked on it.
    Even when it's affected by corrosion, cleaning it well with contact cleaner is the solution, not replacing it as you're unlikely to find one with such a low temperature coefficient as the original one.

    I suggest reading this: https://fixyouraudio.com/tutorials/wow-and-flutter-my-know-how/. My personal thought: lubrication of rotating parts, new good quality rubber (pinch roller + belts) and a capstan roughening are the first steps to take before assuming anyting else.
    If doing these does not imporve the situation at all, you can start suspecting the motor itself or the motor drive circuit. If the motor has 4 wires (internal FG coil) you can measure the frequency of signal on the 2 purple wires and you will see if there are any significant variations.
    Motor looks similar as one used in TC-150, which has an internal FG.

    NOTE: If you cannot find belts specifically made for this device, you can always measure the diameters using cheap belts and order by diameter instead. DeckTech would be the recommended source, as Marian's thickest belts are only 0.8mm. These look to be 1mm or 1.2mm thickness.
     
    Last edited: Mar 8, 2022
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  5. jacobsteel

    jacobsteel New Member

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    Thank you all [ @Valentin @Arky Malarkey @Deb64 ] !

    I performed a 2nd, and then a 3d cleaning+ lubrication and gradually things improved.

    Notes: Taking everything apart and polishing (even shining metal, and even on the inside of bushings) helped more than I would've thought initially.
     
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