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Sony Betamax SL-20 - will almost work, need help

Discussion in 'Troubleshooting and Repair' started by Josh_dsl, Sep 8, 2016.

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  1. Josh_dsl


    Sep 8, 2016
    At work we have a Sony Betamax SL-20 player in our digital archives lab. It has been sitting for maybe around 6 months. It was purchased through ebay, and is suppose to be in working condition. It turns on, rewinds, fast-forwards, and appears to play. The tape looks like it is spinning inside the Betamax, the reel on the tape spins slowly but it does not move through the betamax player. The mechanisms inside the machine, with the cover off, appear to spin and move properly but they do not engage the tape properly, feeding it through. The image is blank.

    I can not find information on this issue on other forms. Please let me know what you think.

  2. shrtrnd


    Jan 15, 2010
    Google for a schematic on your unit.
    Maybe the capstan motor, maybe worn/deteriorated rubber wheels, maybe gears not fully engaging.
    Most Betamax units had an operator manual and a service manual available, and since hardly anybody
    uses them anymore, there may even be some manuals available on ebay for cheap(?)
  3. 73's de Edd

    73's de Edd

    Aug 21, 2015

    Sir Josh_dsl . . . . .

    Am I properly remembering from 32 years back ?

    I also, have either a SL 15 or 30 in my equipment archives . . . saved just in case I needed to play or dupe a Beta tape, or do an off the air capture of some FINE quality stored video . . . . to later transfer over to another media.

    The VERY first Beta units, were some real heavy mechanical kluges and then a refinement to simpler mechanics and then a final transition to dedicated servo controlled, smaller tape transport motors.
    I believe that this one fell into the intermediate category where the capstan drive used a controlled motor and a larger flywheel and belt drive.

    Use my mechanical example below, of your unit and then compare my description of its operation, to what you are seeing happen on your unit.
    Initially there is the insertion of the tape and its being pulled inside of the unit and the cassette drops down and opens the end flap of the cassette.
    The tape is also positioned such that there is a threading roller sticking up just inside of the visible internal video tape.
    Almost immediately, after the cassette fully seats down, there is a WHIZ-WHIRR-BUZZ of the tape threading mechanism seen over to the right rear, where you see that intercoupled COGGED BELT driven mechanism.
    That threading roller pulls out tape and transports it around into that YELLOW path route into what Sony calls a "full wrap" around that round, massive head /drum assembly to the left.
    THEN you should hear a feeble thump of the black rubber pinch roller being spring pressed into the capstan drive spindle.

    Look at the illustration and you see the RED arrow pointing down; enshrouded within that pot metal castings center, is the end of the hardened vanadium steel capstan drive spindle.
    That capstan spindle extends downwardly and terminates within a cast pot metal flywheel.
    Looking back to the top, concentrating on that pot metal shroud, you see that is cut away with a wide slot that lets you see the exposed capstan shaft.
    There is the threaded video tape that is resting against the capstan shaft, and to the OTHER side of the videotape is the black pinch roller (Illustrated as a BLUE circle).

    Possibility 1 . . . . .

    Now . . . . a stop to examine the very-very simplest possible fix of all.
    Using my 35 yr cognitive memory retention ? again . . . . . on the front pushbuttons, check the PAUSE button. I want to think that is incorporating a mechanically latched action, whereupon, if you push that button, it moves in just a bit and mechanically latches into position. The ACCOMPANYING electro-mechanical action that it then produces, is to mechanically let up pressure of the pinch roller to the capstan drive shaft so that the tape STOPS its movement.
    YOU is now paused!
    Then, on touching the PAUSE button again, that button then mechanically comes unlatched and makes a very small movement outward.
    The accompanying electro-mechanical action is to mechanically reinstate pinch action to the capstan drive . . .the videotape then moves again.

    Possibility 2 . . . . .

    Is that you drop the bottom cover plate of the unit and then hope to see that flywheel that I mentioned that the capstan shaft is being driven by.
    Its far beyond me to remember if its then being readily visible, or if a bottom PCB has to be swung down for acquiring visual access of that flywheel.
    Then, I sort of expect to find a broken capstan drive belt laying down in the bottom of the machine . . . . .OR ELSE. . . . . one that has stretched/sagged SO MUCH,
    that it is slipping and producing no drive to the flywheel / capstan drive shaft.
    It takes some OOOOOOMPH to initially get that flywheel started.

    Now . . . . . . . go ye forth . . . . .and . . .check it o . . .u . . .t !

    Th . . th . . th at's all folks . . . . .

    Un Illustratione du le SL20 Sony Meta Bax:

    Sony SL20 Beta Maax Mechanico.jpg

    73's de Edd

    Last edited: Sep 9, 2016
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