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restoring an emerson antique tv

Discussion in 'Electronic Repair' started by Mike, Oct 24, 2003.

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  1. Mike

    Mike Guest

    ive been trying to restore an emerson model 663B.

    i found out the weakness of the picture was the ion trap being on wrong.

    the picture is now bright sharp and crisp.

    everything works now, except for 2 problems. the horizontal is VERY touchy,
    and the sound is weak, but i think i know whats wrong with the sound.

    here is what i want to try to solve.

    i got the set to work fine, but the horizontal wouldnt lock when turning the
    hold control.

    i went to the back and adjusted the horiz. freq. adjustment and it showed up
    as multiple images on the screen, and i adjusted the hold control to get the
    picture to lock into place. but here comes the problem:

    the control is very touchy, you have to have it dead on to lock. and the
    main problem is, lets say its on a scene from a program, and the picture is
    locked in place. well, if the scene changes, like if it gets darker or
    brighter, or if the scene moves, the horizontal is out again.

    i readjust and get it to lock, and when the scene changes back, its gone
    again.

    but if i leave the lock alone, it will lose horizontal, and when it comes to
    a scene similar to the one i adjusted it on, it slows down to a stop and
    locks again, until the brightness, or the scene changes in any way, and the
    horizontal jumps all over the place.

    I dont have any trouble with the vertical, its as stable as can be,
    although,
    there are retrace and forground dashed lines that change at different scenes
    that drive me nuts, but ive heard thats from too strong of signal.

    Any ideas would be appriciated.
     
  2. jakdedert

    jakdedert Guest

    Have you replaced all the paper caps in the horizontal section, and checked
    or subbed the oscillator tube?

    jak
     
  3. Good point! These days whenever I get into *anything* that has those old
    paper caps in there they _ALL_ get replaced. No point in screwing around
    with those, if they're not a problem now they will be later on.

    Also, in something of that vintage there will be a separate sync separator
    stage. This will possibly be tied in with or even combined with AGC
    functions, and a mis-adjustment of the AGC control might produce the
    symptoms described. I'd also check out any high-value resistors in that
    area, I've seen ones (<=1M) that have drastically increased in value from
    age. (Whoops! Dating myself here... :)
     
  4. john

    john Guest

    Maybe the set has one of those
    Double Diodes that was common
    back then,some were soldered in
    and some plugged in.
    Look in and around the Hor/Sync
    section and see if it uses one of them.

    kip
     
  5. Jerry G.

    Jerry G. Guest

    It has been over a 35 years since I have worked on these types of sets! I
    cannot remember details, or have any service information about them.

    Try the horiz oscillator tube, sync separator, sync amp, and video amp
    tubes. Also, at the same time, check all the capacitors, and high omage
    resistors involved. The combination of all of this mentioned will be the
    fault area to fix the set. Considering the age of the set, you can repair
    the rest of the faults if you take the time, and have the skills. If you
    have a scope you can trace the sync signals to see if they are correct in
    specs. Take care that in the horiz sync area, the sync reference feedback
    can trigger the scope, and give a signal that looks like the proper sync
    signal. This can fool you.

    For the horiz sync lock, there is a feedback from the horiz output stage to
    the sync control, which is part of the sync detector, and or the oscillator.
    The feedback pulse is compared with the sync pulses coming in. They make a
    type of servo DC correction to guide or hold the oscillator in place or
    phase locked.

    The AGC is also an area of problems with these sets. Improper AGC operation
    will make the picture bend, have poor phase lock, be over contrast
    (depending on how it is not working), and also may introduce buzz in the
    audio.

    When you fix the set, you will have a very good set!

    --

    Greetings,

    Jerry Greenberg GLG Technologies GLG
    =========================================
    WebPage http://www.zoom-one.com
    Electronics http://www.zoom-one.com/electron.htm
    =========================================


    ive been trying to restore an emerson model 663B.

    i found out the weakness of the picture was the ion trap being on wrong.

    the picture is now bright sharp and crisp.

    everything works now, except for 2 problems. the horizontal is VERY touchy,
    and the sound is weak, but i think i know whats wrong with the sound.

    here is what i want to try to solve.

    i got the set to work fine, but the horizontal wouldnt lock when turning the
    hold control.

    i went to the back and adjusted the horiz. freq. adjustment and it showed up
    as multiple images on the screen, and i adjusted the hold control to get the
    picture to lock into place. but here comes the problem:

    the control is very touchy, you have to have it dead on to lock. and the
    main problem is, lets say its on a scene from a program, and the picture is
    locked in place. well, if the scene changes, like if it gets darker or
    brighter, or if the scene moves, the horizontal is out again.

    i readjust and get it to lock, and when the scene changes back, its gone
    again.

    but if i leave the lock alone, it will lose horizontal, and when it comes to
    a scene similar to the one i adjusted it on, it slows down to a stop and
    locks again, until the brightness, or the scene changes in any way, and the
    horizontal jumps all over the place.

    I dont have any trouble with the vertical, its as stable as can be,
    although,
    there are retrace and forground dashed lines that change at different scenes
    that drive me nuts, but ive heard thats from too strong of signal.

    Any ideas would be appriciated.
     
  6. Mike

    Mike Guest

    i will provide you with all the information:


    i bought this set on ebay, and it was freight damaged. i replaced the
    shattered picture tube, and replaced ALL paper and electrolytic caps.

    i had to replace some tubes due to weak emission, and replace the choke, as
    it was open when someone in the past tried to power it up with bad 'lytics.
    i also found open and replaced the only ballast resistor, and i replaced the
    focus resistor as it went from 1 megohm to like 5 megohms. I have the sams
    to the set, and absolutly no diodes whatsoever. i believe the set was made
    in '51

    thanks for your input, and if someone would lead me in the right direction,
    id appriciate it.
     
  7. Bob M.

    Bob M. Guest

    I can't really give you anything detailed, just some theory.

    The AGC will control the overall amplitude of the video signal. Depending on
    the polarity of the video detector, the sync pulse level will either be a
    positive voltage or a negative one, and the peak white level will be the
    opposite. For now, let's just assume that sync is negative and peak white is
    positive. The NTSC standard would allow for 140 IRE units from sync tip to
    white level, with sync at 0, black level at 40, and peak white 100 units
    higher at 140. The DC levels must be maintained so the sync separator can
    detect the difference between black and sync tips. As you noted, when the
    picture has more white in it, the DC level is probably shifting, so the sync
    sampling point shifts, and you lose sync lock.

    There could be a DC restoration circuit in there that will attempt to
    maintain the DC level for black. But if the AGC circuit isn't working
    properly, or isn't adjusted the way it should be, then the amplitude of the
    signal could be way off or even vary with picture content.

    It's also been a long time since I fixed a tube set (over 35 years) so I'm
    going on a lot of recall here. Hope this helps a bit.

    Bob M.
    ======
     
  8. David

    David Guest

    Are you sure there are no diodes in the horz. afc circuit? Many of these sets had a set of two selenium diodes molded into a plastic assembly with three leads on it. There were several configurations including common anode, common cathode, and series connected. These often failed resulting in very poor or no horizontal sync.
    Dave
     
  9. Mike

    Mike Guest

    I fixed it. stupid me, i had the caps backwards in the sync seperator. the
    sync seperator tube 6au6, the coupling cap was accidently grounded, instead
    of coupled into the sync amp tube. so, there was the problem.

    the sync both vertical and horizontal is locked on tight. no drifting, but
    there is a problem in the AGC. because when the scenes get brighter, the
    picture begins to tear and notch horizontally, like your watching
    macrovision, or a scrambled cable channel. but it only does it on bright
    scenes. it works perfect on normal to darker scenes.

    any ideas will help.







    Are you sure there are no diodes in the horz. afc circuit? Many of these
    sets had a set of two selenium diodes molded into a plastic assembly with
    three leads on it. There were several configurations including common anode,
    common cathode, and series connected. These often failed resulting in very
    poor or no horizontal sync.
    Dave
     
  10. john

    john Guest

    Never seen a TV yet that has NO diodes.

    kip


    Are you sure there are no diodes in the horz. afc circuit? Many of these
    sets had a set of two selenium diodes molded into a plastic assembly with
    three leads on it. There were several configurations including common anode,
    common cathode, and series connected. These often failed resulting in very
    poor or no horizontal sync.
    Dave


    no diodes whatsoever. i believe the set was made
     
  11. Mike

    Mike Guest

    nope, none. absolutely zero.

    i have the sams sitting right in front of me.
     
  12. john

    john Guest

    Well I can name you 2 diodes in there without even looking at the schematic.
    One begins with D and the other begins with S.

    kip
     
  13. Mike

    Mike Guest

    sorry, dude. there is NONE.

    the only thing diode-like are 2 rectifier tubes. 2 rectifiers each tube.

    one is in the sound circuit, the other is in the IF circuit.

    otherwise, NO DIODES.
     
  14. john

    john Guest

    Now you are getting close,what is a rectifier ?

    kip
     
  15. Jason D.

    Jason D. Guest

    When you finally understood, that is excellent.

    Rectifier, Hahaha... I wasn't from that era (born 1972) but I read
    about old stuff and have yet to work on tube based TV set. Mind you,
    I took apart several of them including one with 200+ colored pots with
    triple convergence coils for the CRT when I was young.

    Now about that one, rectifier yes I know what it is. Diode word &
    symbol wasn't there back then. Think about it, Hot filment emitter &
    cold plate all in a hard vacuum, what happens to those electrons flow?

    Now read about why diode was called solid-state rectifier (another old
    name.). A tiny slab of silicon doped with two types of dopants too
    full of electrons atoms and holes where atoms had lost several
    electons seperated by a "line" as junction. Again, find out why this
    works this way.

    Oh, the oddly shaped tube is still here and it's staring right in your
    face is it too!

    Cheers,

    Wizard
     
  16. john

    john Guest

    The first diode; a vacuum tube diode was developed by J. Ambrose Fleming in
    1902.



    Just for reference..



    kip
     
  17. Asimov

    Asimov Guest

    "Mike" bravely wrote to "All" (25 Oct 03 15:30:23)
    --- on the heady topic of "Re: restoring an emerson antique tv"

    The ACG action was "keyed" and required a properly timed pulse from the
    horizontal section. The coupling cap would often open up due to the
    higher voltages found there.

    Aside from that, if the AGC voltage is 0, could be the tuner AGC bypass
    feedthrough is shorted out. That used to happen from time to time and I
    don't know why. Just reroute the wire with a 1nF (or so) cap to ground.
    I replaced one once but it was a lot of trouble.


    Mi> From: "Mike" <>

    Mi> I fixed it. stupid me, i had the caps backwards in the sync seperator.
    Mi> the sync seperator tube 6au6, the coupling cap was accidently grounded,
    Mi> instead of coupled into the sync amp tube. so, there was the problem.

    Mi> the sync both vertical and horizontal is locked on tight. no drifting,
    Mi> but there is a problem in the AGC. because when the scenes get
    Mi> brighter, the picture begins to tear and notch horizontally, like your
    Mi> watching macrovision, or a scrambled cable channel. but it only does it
    Mi> on bright scenes. it works perfect on normal to darker scenes.

    Mi> any ideas will help.

    .... I worked hard to attach the electrodes to it.
     
  18. Peta

    Peta Guest

    These TV sets were renowned for using variable resistor pots that do have tracks
    in the pot that break. Check that the track is not broken and second has someone
    replaced the pot at some time with a value that is to high. Try a pot with a
    lower value. Do this in steps if it seems to help. Next check the resistors that
    will be in series with the pot, they may have gone high in value. Lastly don't
    look for the difficult solutions look simple it usually is. all the very best
    Peta***
     
  19. Mike

    Mike Guest

    would a weak horiz ocillator tube cause AGC problems?

    i put the 6sn7 on the tube tester, and out of a scale of 100% emission, its
    reading 30. hmmmm.



     
  20. Yes it would. AGC in lots and lots (most?) of tv sets is _keyed_ by a
    horizontal pulse. Often this comes off the flyback, but not always.
     
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