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Thread: Questions About the TU56 Tape Drive

  1. #11
    Join Date
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    The MAINDECs for the TD8E are very comprehensive and complicated so I made some very simple tests for the TD8E.
    One will copy the console switches to the Command Register. This will let you move the tape forward and backward.

    Simple TD8E Tests in PAL
    Simple TD8E Tests listing
    Simple TD8E Tests in RIM
    Member of the Rhode Island Computer Museum
    http://www.ricomputermuseum.org

  2. #12

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    Quote Originally Posted by bobaboba View Post
    The Ďbig capacitorsí will certainly need changing and probably already started to leak.

    Anders - how did you manage to use Ďmuch smaller plastic onesí? These are motor run (not motor start) capacitors and Iíve not seen any particularly small ones at the rated voltage. The ones I used were almost exactly the same size as the originals, maybe even a bit wider.
    I used those: https://eu.mouser.com/ProductDetail/80-R60EW61005000K 100uF/100V

    DSC_1518_00002.jpg

    I should really print some holders to those...

  3. #13

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    I would say, check the capacitors first. My drive is still running with the original capacitors.

    Maybe an idea to think about...
    I've restored many radio and TV sets and I always tried to keep the looks as original as possible. This is an example
    of what I did in a Bush TV22 set. These capacitors are also mounted in a clamp at the bottom just like the TU56.

    I used a pipe cutter to cut the capacitor at the point where it is in the clamp. Pulled the innards out and glued a
    piece of wood in the bottom. Then there is still enough space to hide modern capacitors inside the old one.
    Just drill a few little holes next to the terminals for the wires.

    capacitor repair.jpg

    When it's back into the clamp you never see the difference.

    Bush TV22F 15.jpg

    If you want to do this, please wear hand cloves and do it outside. Or better in a fume hood.
    But it might be an idea to think about... (Oh and never open up oil can capacitors due possible PCBs in the oil...)

    Regards, Roland
    WTB: Case for Altair 8800 ...... Rolands Github projects

  4. #14

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    Quote Originally Posted by anders_bzn View Post
    I used those: https://eu.mouser.com/ProductDetail/80-R60EW61005000K 100uF/100V

    I should really print some holders to those...
    Wish I'd found those. The ones I used are actually a bit bigger than the originals and I had to bodge a mounting for them.
    Ah well - works OK.

  5. #15
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    So is there consensus among the "electronitions" that these caps will do the job? And to verify that the only issue is rating, not that there is some magic "starting stuff" inside a start cap (versus a run cap)?

    I could certainly use a couple of sets!

  6. #16

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    There is no such magic. I use them and Mattis use them (got the tip from him). I have been running my (well borrowed) TU56 for quit some time now and it works just perfect!

  7. #17

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    Starting capacitors are generally rated for intermittent use. Normally they’d be in circuit for (much) less than a second on a small/medium motor. Run capacitors are continuously rated as they are in circuit the whole time the motor is running. My view FWIW is that these capacitors are surprisingly small for continuous running. The only difference from a practical viewpoint is prospective lifetime. Hobbyist TU56s don’t generally run all that much.

  8. #18
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    As noted, extended capacitor lifetime isn't an issue for most of us, but I'd be interested in failure mode - I don't want to introduce another "RIFA situation" with spectacular fails to anticipate.

  9. #19

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    The classic failure mode is localised dielectric failure due either to overvoltage (eg supply/inductive spikes) or manufacturing deficiencies, but after that there are various possibilities. They tend to self heal by evaporating the conducting path, but itís possible for the heat generated to become destructive for instance if the failure is repetitive or becomes resistive rather than open. Because dielectric failures arenít uncommon there are some design approaches which try to minimise the chances of destructive failures. Iíve seen them swell up and emit a cloud of smelly smoke. As usual too big a subject to ramble on about here.
    Iím sure that Murphy had heard of them too.

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