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DAT "video" head replacement?

Discussion in 'Electronic Repair' started by N_Cook, Sep 5, 2013.

  1. N_Cook

    N_Cook Guest

    Sony DAT audio DTC 690 drum assembly/ DOU-03A/ 8-848-567-11
    Initially, anyone know how to get the top drum off, I don't want to heat
    up to separate interference fit , if there is some secret fixing.
    Then anyone happen to know if video heads are the same, they look the
    same via what little I can see of them.
     
  2. N_Cook

    N_Cook Guest

    I can't make things worse. Smashed up heads, probably from foam breaking
    up / snagging on the silly "head-dirtier" arm
     
  3. N_Cook

    N_Cook Guest

    I managed to make a small hub puller out of an old pair of basic wire
    strippers and circlip pliers and a minute of low heat from a hot air gun
    to pull the 6 pole magnet disc from the underside, without damage. After
    taking measurements of the 2 gaps, to the nearest thou. Next week I'll
    try removing the top disc from the middle disc, again interference fit
    and again nothing to really get a hold of for hub pulling action.
    Probably will be some protective tape around the bottom drum (non tape
    path part) then a l
    jubilee clip as I don't think the few 1.5mm threaded holes in aluminiun
    would take the strain.
     
  4. nice.

    just curious, who even sells DAT heads, let alone in 2013?
     
  5. Guest

    Good question. ASTI doesn't have them and everyone who says they can backorder them prices them at arouind $800.

    Gotta have a real need.....
     
  6. N_Cook

    N_Cook Guest

    Available at Megabucks.
    Discovered one thing, so far. There are 2 magnets on the disc I removed.
    The disc is probably mu-metal with strong 6 pole motor magnet below and
    a weak thin disc above to energise a castellated pcb track for a tacho.
    I suppose the mu-metal is to stop the rotating main field from directly
    coupling with the heads or the transfer coils,one pair is static and one
    pair rotating relative to the magnets wheras the video heads are static
    relatively speaking, and the weak one is too weak to affect more than a
    couple of mm away from it
     
  7. N_Cook

    N_Cook Guest

    I've decided , when I get back to it , to drill matching 8 holes in a
    plate and hope 8x 1mm screws, 5 threads each, will hold in place while
    trying to separate the 2 drums
     
  8. Guest

    Yes, but that doesn't solve the "betamax syndrome".

    This is when you have a bunch of beta tapes of your kids and all that and you haven't dubbed them or anything and absolutely positively must have a beta machine to play them.
     
  9. Guest

    Bought an SLHF-300 (Beta) on eBay last week for $70 total. It works fine but I blew out a LOT of dust before cleaning and checking it.

    It seems better than half the Beta machines on eBay are 'for parts or repair'. I have an SLHF-900 I'm sure has a bad cap or 2 preventing the capstan servo from locking. Just too lazy to get out the scope so the $70 was my easy way out.

     
  10. qtips on flying heads is always bad news. They'll snag and shed. I've
    always used acetone and plain paper for cleaning such heads. It works
    great.

    qtips and acetone for the path and capstan and pinch roller. A soft dull
    screwdriver tip can scape edge of the tape crud off a capstan.

    Some heads (well the drums) looks pristeen but no longer function. Some
    cruddy looking ones still work fine. Anyways, if the cover comes off,
    everything gets cleaned.
    Somebody want want to play back some dat tapes. In the video world,
    cleaning tapes are pretty pointless as they can't clean the path.
     
  11. N_Cook

    N_Cook Guest

    7x 1mm screws with little washers and pads of silicone under the heads,
    through holes in a plate with a reaction frame fitted, and screwed to
    the DAT drum. 40 seconds of low heat hot air and the circlip pliers as a
    lever and the bottom drum came away. Leaving the ball race on the drive
    and the drum separating from the outer section of the race. Upper
    ferrite former for thre upper coupling coil seems to be glued to the
    central lump. Desoldered at the 4 solder joins but not yet tried heating
    the ferrite to see if it comes away. Under that is the head mount
    screws. The heads are about 80% the size of VHS heads, and certainly
    thinner, will have to find a scrapped 8mm set of heads
     
  12. To the best of my knowledge, this is not correct. VHS has little or no gap
    between the stripes, nor does Betamax. That's what "Betamax" refers to --
    maximum surface coverage, "bet" being the Japanese word for surface coverage.

    Because the luminance signal is FM, a bit of leakage causes no harm, as the FM
    capture effect can be used to eliminate it, by limiting the signal. The
    chrominance signal is AM, and an alternating- or rotating-phase carrier is
    used to minimize crosstalk.
     
  13. "Gareth Magennis" wrote in message
    I don't think that's true -- how would you separate the tracks? But I'd better
    not "take sides".

    I do know that some decks have two heads -- rather than one. This allows
    off-the tape monitoring, just as in three-head analog deck -- at the expense
    of greater tape wear.
     
  14. "Gareth Magennis" wrote in message "William Sommerwerck" wrote in message
    Kind of?

    Then point me to a reference. Virtually all of the online material is in SMPTE
    or AES articles, which you cannot access for free.
     
  15. Guest

    The ATS must work the same way it did in the 8 mm. video decks. In them, there are four rotating frequencies used. The primary on track frequency is the strongest coming out of the head, two other frequencies are expected at lower levels. The capstan motor is adjusted by the servo to equalize the two off track frequencies.

    At each pass of the head it uses a different frequecy for the on track frequency and of course it expects two other frequencies just the same as last time.

    There are four frequencies and the reason for that rather than just three is to keep it from getting confused. When F1 is recieved it KNOWS it is looking for F2 and F4 for example, then when F2 is on track it looks for F1 andF3, then when it goes to F3 it looks for ........ I forget. It doesn't matter, but this should illustrate the reason to use four frequencies rather than only three. It assures the proper operation of the servo because there can be no mistake about which track is leading the "on" track and which is lagging.

    This system eliminates the need for a control head and errors introduced due to tape stretching. The 8 mm. decks did actually usually have a sub audiohead but I doubt it was ever used except maybe in some super cheapo deck which didn't even make it to market. It may have been used for a tape counter as well, I simply don't remember those details.

    Interestingly there were decks that used the 8 mm. tape strictly for audio.The tape wrap was actually greater than 180 degrees and one sector was used for digital audio tracks. These were not the greatest format in the worldbut they beat BTSC and were good enough for music, as in better than most cassettes. The 8 mm. decks with the feature to go all audio simply used more sectors for more digital all audio mode. If you recorded say tracks 5 and6 on a tape that had video on it you would see a band across the screen where the new audio tracks were recorded. The system also had the drawback ofhaving to completely rewind before playing the subsequent tracks.

    Needless to say these things did not get a huge market share. I just know about them because I worked for a high end Sony dealer.

    This is completely different than the auto tracking feature in any VHS deckand I am unaware of automatic tracking being incorporated in any Beta deck, though I might not have seen them all.

    Additionally, in the DAT formet I don't know, and I simply don't remember on the 8 mm. decks if the actually recording carrier frequency was rotated or if they were like "pilot" frequencies simply chosen not to interfere withthe signal, but it really doesn't matter. That's how such a system works.
     
  16. N_Cook

    N_Cook Guest

    Here is a rare beast, pics of innards of a DAT drum
    http://www.diverse.4mg.com/DAT.jpg
    top views at top, 1mm squared paper and one of the 1mm screws I used.
    The ring of white dots in image lower1 is where the middle ferrite disc
    was superglued? to the central boss. I tried 20 seconds of 300 deg C
    heat and trying to break the bond with a screwdriver blade, cracked the
    ferrite, so the splodges are my superglue additions. 30 seconds of heat
    and a smell of varnish or something and the bond broke.
     
  17. N_Cook

    N_Cook Guest

    I forgot to include the motor section in those pics
    I raided an 8mm video head drum. Heads about .2mm thicker (with the pcb
    sliver) than DAT ones ,probably room , width 0.9mm wider , probably room
    wit a chamfer on either side. Radial depth would need 3mm cutting off
    and the fitting hole moved but as no precision there, probably feasible.
    Strange, I've never removed an individual video head. I always wondered
    how the head-coil ferrite could be mounted with epoxy on the brass
    section with any precision. Now I see they use shims under the brass.
    The one I looked at marked 76 , presumably 76 microns. I always thought
    the mounting surface was a reference plane but not so, each head must be
    assigned a shim , on test, before fitting. No idea whether 8mm and DAT
    use the same reference plane and no idea how to set the video heads
    before screwing down in place. When I have time I may have a go at
    adapting and trying
     
  18. Guest

    "And just one more thing, the Alignment Tapes required to align the tape path
    I believe were specially recorded with no ATF signals,"

    OK, so they were separate frequencies, not the carriers.

    However the lack of ATF signals is not required to align the deck. You still just align it, although you might confuse the system.

    Most likely with a print you can find a way to disable the ATF system altogether, even if you have to disconnect the output from the heads. Believe meit can be done and should be done on a customer tape recorded previously in that machine, partly because compatability with other machines is not likely to be a big issue. For alignment I would get the tape tension as low aspossible.

    You know they said you needed all this equipment to align the old VHS recorders that had pots for the FM deviation and frequency and all that shit. Know what I did ? I just coupled the record signal to a deck "playing" a blank tape and "tuned it in". There is almost always a way, and remember, they are in business to make money.

    This is digital so it is nowhere nearly as critical. Just get a good envelope out of it and it will be fine.
     
  19. Guest

    "I forgot to include the motor section in those pics "

    Yeah well the whole URL didn't work for me so it is no big deal on this end.

    You should be able to do this without an alignment tape and all this shit, but I would not go drilling holes in it
     
  20. N_Cook

    N_Cook Guest

    I have to wonder why they did not make the heads disc easily removable
    like a video recorder and ,so, if there was a cheap and cheerfull
    generic way of replacing the innards of "over a barrel" company-supplied
    drums
     
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