Image Map Image Map
Page 2 of 5 FirstFirst 12345 LastLast
Results 11 to 20 of 41

Thread: Apple IIc Monitor Tube displaying strange behavior

  1. #11
    Join Date
    Sep 2016
    Location
    Melbourne, Australia
    Posts
    629

    Default

    I'd replace the diodes before I started blaming the yolk. The diodes are damper diodes to prevent the deflection voltage across the coil going negative and ringing, which is what I suspect is happening.
    The voltages across those coils is not terribly high but the speed of the diode will be important on the horizontal yolk coil because it runs at over 15KHz. Looking at the diodes in question they look identical to the fast recovery diodes uses in the apple power supplies.

    Something like a HER305 should do the trick.

  2. #12

    Default

    Having reread the OP, I think my tube swap suggestion has already been carried out. In that case, it must be the yoke.

  3. #13
    Join Date
    Oct 2008
    Location
    Kamloops, BC, Canada
    Posts
    5,659
    Blog Entries
    43

    Default

    I would also opt for a yoke swap as on monochrome tubes they are WAY easier to adjust back than color tubes.
    = Excellent space heater

  4. #14
    Join Date
    Jan 2012
    Location
    Connecticut, USA
    Posts
    2,129

    Default

    Thanks for all the insight Guys. I will do a resistance check on the yokes as well as resistance checks. David_M I will try those Diodes as well thanks.

  5. #15

    Default

    Quote Originally Posted by Hugo Holden View Post
    If the yokes are the same part, one must have some shorted turns in the vertical coils. The H scan coils look OK probably. Sometimes you can see a turn of wire on the yoke near the surface with other are crossing it at nearly 90 deg,with gaps, if you see a configuration like this you can try to move the wire a little , sometimes the shorts can be near the surface and you can get lucky. The CRT itself is probably fine.
    If the problem is in the vertical coils, they're also easy enough to be rewound even by hand, they are the external ones. I'd try rotating the yoke 90 degrees to see if the symptoms rotates also by 90 degrees on the screen.
    Vertical coils are sometimes connected in parallel, maybe some connection is missing, or as Hugo said, it's a short somewhere.

    Frank

  6. #16

    Default

    Quote Originally Posted by iz8dwf View Post
    If the problem is in the vertical coils, they're also easy enough to be rewound even by hand, they are the external ones. I'd try rotating the yoke 90 degrees to see if the symptoms rotates also by 90 degrees on the screen.
    Vertical coils are sometimes connected in parallel, maybe some connection is missing, or as Hugo said, it's a short somewhere.

    Frank
    That is a good thought, I have the schematic but I'm not at home. Most of the time in smaller monitors it is the H coils that get wired in parallel to keep the resistance low and they don't require as much total inductance either, but if it was a design where the V coils got wired in parallel, then it is possible that one could be open circuit and it is not a short.

  7. #17

    Default

    Rotating the yoke won't help... Swapping coils (horizonal to vertical) is probably not a good idea.

  8. #18

    Default

    Quote Originally Posted by KC9UDX View Post
    Rotating the yoke won't help... Swapping coils (horizonal to vertical) is probably not a good idea.
    Yes I agree, generally the H coils have a much lower inductance and resistance than the V coils, so it's not a good idea to swap them.
    If the OP has an inductance meter it's another good way to compare the V coils on the two yokes, aside from checking their DC resistance.

  9. #19
    Join Date
    Jan 2013
    Location
    Marietta, GA
    Posts
    3,210

    Default

    I think the idea was just to turn the yoke to see if the same pattern persists, but rotated. Although I am sure it would.

    No H/V plug swapping.

  10. #20
    Join Date
    Jan 2012
    Location
    Connecticut, USA
    Posts
    2,129

    Default

    Hugo if you have the schematic when you are home, please let me know. Here are some photos of the CRT. What is that strange outer coil? An inductor? 20190719_230433.jpg20190719_230439.jpg20190719_230414.jpg

Bookmarks

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •