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Doubled up video head appearence?

Discussion in 'Electronic Repair' started by N_Cook, Sep 17, 2013.

  1. N_Cook

    N_Cook Guest

    Video 8 head disc, 3 heads but 4 coils marked
    A and B on opposite sides of drum
    head FE ,and combined head JOG on same mount as B
    no pic found on gogle pics
    Trying to determine what a doubled-up head loks like , as before
    demounting the drum I thought it was 3 coils , with one of them the
    ferrite gap section broken away , but now inside looks like 2 purpose
    made separated ferrite end forms, ie not fractured. On Sony EV S700 ,
    from SM, FE is probably Flying Erase. I may attempt a pic of what is here
     
  2. N_Cook

    N_Cook Guest

    a close-up pic of Sony EV S700 , video 8 JOG, doubled up head
    http://diverse.4mg.com/video8.jpg
    ignore the well in the aluminium, dark enamelled coil on left, clear
    enamel on right and two dark glass/ceramic linear features with a large
    gap, compared to normal gap, as designed or part broken away?
    As rounded edges, I would say as designed
     

  3. I think you mean "dual azimuth", not "doubled up".

    The picture is of one but it's difficult to say if it's broken, the ferrite
    material is hard to see.

    Generally it was one peice of ferrite with two cuts in it, one side was
    "wider" than the other and the two heads were separated by a finger from the
    cuts.

    If anything, it does look like the side by the red coils is broken towards
    the center, where the finger would be, but like I said, is hard to say from
    that picture.

    I don't think parts for those were much available past the mid 90's but keep
    in mind I think that machine was also marketed as a Pioneer VE-D70. That one
    I might still have the service manual for, not sure.

    -bruce
     
  4. Guest

    I disagree, I think it's broken away.

    The 8 mm. decks didn't have four heads like a VHS, in fact Betas also did all effects with only three heads. What that dual head is I'm pretty sure isthe opposite azimuth to pick up a second field for still/pause. They sharea center pole piece. The still image is field/flield, not field/frame. I know that's not exactly how to put it but think a minute and it makes sense.

    After all if it was field/frame and you just happen to hit wrong, any significant motion would cause a "flutter" of sorts. You have probably seen thison EP from a low end, two head deck. The third head prevents that anomaly by repeating the same field.
     
  5. N_Cook

    N_Cook Guest

    SG once of this parish
    http://www.repairfaq.org/sam/head6.gif
    is the only pic I can find
    one broken and one good dual head.
    I see now that the central ceramic pillar of only about 0.2mm width that
    has a few shared turns of dark and clear wire would have had an
    extension out and then 2 now missing gaps, no wonder they break , there
    is hardly any meat to that sort of construction
     
  6. N_Cook

    N_Cook Guest

    arranging the light and viewing a bit better, one gap and its ferrite
    pillar is still present. I think I'll try grinding up some ferrite with
    epoxy , prefit a piece of mica for the gap and add a blob of ferrite
    plus epoxy. If its possible to retrieve something then probably better
    than nothing, if a few hours of lowest frequencies of the most
    significant audio can be retrieved. Will try on insignificant tapes
    first and wait for something to turn up on ebay and keep this in reserve
    for the no-turn-up situation (assuming anything comes out that is)
     
  7. Guest

    Wait a minute, you mean there are only three heads total ? I mean only six wires to the thing ?

    In that case it is not a trick head it is the erase head.
     
  8. N_Cook

    N_Cook Guest

    There are 4/5 head coils, 4 pairs of wires going down tothe rotary
    coupler coils but 3 lumps of brass with heads on, one head with 2/3
    coils on it. I think the complex one was 3 coils but 2 gaps
     
  9. N_Cook

    N_Cook Guest

    The service manual shows 4 heads
    Flying erase
    1'ch
    1ch
    2ch
     
  10. N_Cook

    N_Cook Guest

    What is the connection between Sony & Pioneer?
    Pioneer VE D70
    http://www.1ivanka.de/bilder/S700_F_Pio.jpg
    http://www.1ivanka.de/bilder/S700_R_Pio.jpg

    and sony EV s700
    http://www.totalrewind.org/miniature/photos/evs_gv01.jpg
    certainly look the same, different r/c , not found a Pioneer SM yet
     
  11. N_Cook

    N_Cook Guest

  12. Guest

    "What is the connection between Sony & Pioneer? "

    From what I heard Sony made ALL 8 mm. decks no matter what they're branded.Makes sense, nobody else wanted to tool up for it so they just bought them.. Also there was just a bit of a format war with the rightfully dead VHS-C.

    This is probably good for you because that means that most of them will interchange. Another thing is that it is not like VHS, you can put a head diskin there that does not have the trick head and it will work fine, as opposed to VHS where one set is dedicated to one speed and the other for the other. Actually it CAN be done on VHS by just making the head switch stay in EP and adjusting the PG shifters, if they are DA. If they are discrete headsyou are UTCWAP.

    Anyway, if you do find a head that is otherwise compatible without the trick head all that will happen is you won't have a clear still frame or searchin SP mode. Big deal. I think mostly all the video tape repairs now shouldconcentrate on just getting it to work and dub the content over to DVD or rip it to a harddrive. Screw the trick head.

    I did a quick search and it seem Asti doesn't have it, I found one online used for $75. Really you could probably find a camcorder somewhere cheap, with maybe something wrong with the camera part. Unlike VHS-C the heads are the same as in the decks. Actually I think I have one kicking around somewhere with a defective auto-focus circuit, but I am not so sure I want to partwith it.
     
  13. N_Cook

    N_Cook Guest

    Much useful info there
    At the moment i'm setting up a "right" pentaprism stereo microscope,or
    rather an angle-adjustable mount for the video drum, to try fitting a
    bit of ferrite. Broke a pot core by squashing , so have a goodly
    collection of ferrite bits of about the right size
     
  14. Guest

    I am not optimistic about repairing the head itself. Even if you match the material exactly it still amounts to a crack which will raise the resonant frequency of the circuit.

    The piece will probably break off when you polish it, and you better polish it or it will probably tear up every tape you put in it.

    Your little piece of ferrite is going to have to be firmly stuck in the back, and also have a tiny gap on each side.

    Good luck, you will definitely need it.
     
  15. N_Cook

    N_Cook Guest

    I'm always amazed there is enough signal to come off VCR magnetic tape,
    via little heads and rotary transformer to produce anything of any use
     
  16. N_Cook

    N_Cook Guest

    went back to plan A as my temporary glue method failed to fransfer bits
    of ferrite of sort of dimensions .5x,.3x.3mm.
    Epoxy loaded with ferrite grinding dust, seemed to make a good bridge
    bwetween gap and small coil, probably surface tension helping.
    I will leave to cure until tomorrow but anyone know of an out of machine
    rudimentary test for head functionality? Heads on their own ,
    disconnected from rotary coil, rotating magnet? just so can try on each
    head ,in turn, to compare responses
     
  17. I think you are venturing into new territory.

    The only peice of test hardware I seen to check video heads was from a
    Sencore propaganda sheet. Meaning I dunno if it actually checked anything
    except coil continuity.

    I think the theory was, it injected an AC signal at some frequency to check
    the resonant frequency of the coil and ferrite material, but I don't know
    what they used for a reference.

    Me thinks you would need a good, known working head to find a baseline,
    those kinds of specs were never in print.

    Although it's nice to see someone give it the "old college try", I'd be
    really surprised if anything you are doing will be fruitful.

    Back in ancient times when VHS machines has simple two head designs, A and B
    heads, I had two identical upper cylinders, natually one with a bad "A head"
    and the other with the "B head" broken and tried a transplant between the
    two.

    Even having access to a brand new 3rd one and making multiple measurments of
    every x-y-z measurement I could make, it never worked. I dunno what kind of
    laser-guided robot machine cranked those upper cylinders out, but I really
    doubt a human with a gradient microscope was doing it.

    Just trying to tighten the allen screw that held the head to the cylinder
    shifted things around. There must of been some kind of mold or guide used.

    Remember that gap is around 11 or 13 micrometers, trying to bolt that thing
    to a quarter pound of aluminum (or whatever the cylinder weighs) exactly
    seems like a super human feat to me doing it by eye without reference.

    And you still have the pain the ass of reassembling everything, testing it
    out and if it doesn't work, then what.

    This seems like one of those things to just sit it in the corner and keep an
    eye on ebay for a parts machine. Last one on there only went for $85 and was
    claimed to "be working".

    Anyway, back to the original question, somewhere in the late 80's or early
    90's Sencore did have a device that claimed to test video heads, only
    suggestion is figure out what that was and see if any technical poop is
    available on how they did it. It was one of those "combination" things they
    were good for, some kind of cap/coil tester I'd guess but a later model than
    the LC53, whatever the one was with the LED readout rather than the
    LCD one.

    Rough guess from ebay pictures, you are probably looking for the Sencore
    LC102 or 103.

    -bruce
     
  18. Jeroni Paul

    Jeroni Paul Guest

    I have replaced a broken head in a VHS drum two times and it worked. Not perfect but good enough to use the machine for playback.
    The experience was similar in both cases. Adjust horizontal position so thepicture does not shake and color is stable and adjust vertical so the tracking control behaves similar in both fields. It ends up in a compromise between adjustments as they all interact but the result was a nice watchable color picture.
     
  19. N_Cook

    N_Cook Guest

    By replaced, do you mean robbing a brass plus ferrite plus shim plus
    coil of a head from a donor drum ? what sort of basic/sophisticated
    physical xyz alignment of the head did you do before reassembling and
    and powering up ?
     
  20. Jeroni Paul

    Jeroni Paul Guest

    N_Cook wrote:
    By replaced, do you mean robbing a brass plus ferrite plus shim plus coil of a head from a donor drum ? what sort of basic/sophisticated physical xyz alignment of the head did you do before reassembling and and powering up ?

    VHS heads are screwed in the drum and electrical connections soldered so they can be removed as a chip, see example:
    http://www.danalee.ca/ttt/images/12/sixheaddrum.jpg
    I took a similar head from another drum and installed it matching the position of original head as best as I could by eye. I did some markings on the drum before I took out the damaged head to keep a reference of its position.. Then I did a fine position calibration by watching the resulting video signal, removing and reinstalling the drum back in the machine every time to make small corrections. There is another screw not shown in the photo that sets the head separation against the drum adjustable from the top.
    The video signal tells a lot about head calibration problems. The resultingcalibration was probably not perfect but good enough to get a color noise free picture tested with some commercial video tapes.
     
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