Tech: K7000 vertical foldover problem

Archived from groups: (More info?)

Help! I'm out of ideas. Have a 25" WG K7131 (never done one of these
before) that has a fresh cap kit on it. Prior to the cap kit, had a
black spot in the corner of the tube and picture was the 5" x 8" on the
screen. Did the cap kit and everything works fine except for the
vertical size/foldover problem I am having. Here is what I have done:

Cap kit
Changed C51 tantalum cap
Changed IC4 voltage regulator
checked for cold solder joints and resoldered any suspicious ones
checked diode by c48 (don't remember the number)
adjusted vr9 and vertical size & vertical position with only partial results
Checked Q7 and Q9.

No matter how much I adjust VR9/vertical size, I cannot get the extra
lines in the screen to go away. Interestingly enough, the large
resistor on the side of the chassis is a 180 ohm vs. the normal 220 ohm
resistor. Voltages at both ends of the resistor are as follows:
Back side of resistor(blue wire) 165v
Front side (red wire) 135v

These seem high but I changed the VReg. (IC4) with a new one from Bob
and get the same results. I would have thought the shutdown circuit
would have activated by now.

I'm thinking the large picture is due to the higher voltage. Besides a
possibly bad VReg, wWat have I missed? I'll try a used one from another
chassis and see what kind of results I get. In the meantime, I'd sure
appreciate any ideas.

Photos of the problem are here:

Pat D.
9 answers Last reply
More about tech k7000 vertical foldover problem
  1. Archived from groups: (More info?)

    Looks like your brightness is too high.

  2. Archived from groups: (More info?)

    yikes, I didn't see the separated pixels/lines, brightness is not the
    problem here....
  3. Archived from groups: (More info?)

    You've got the screen control on the flyback turned up too high.
  4. Archived from groups: (More info?)

    Try adjusting the 50/60hz pot. Ive seen this work.
  5. Archived from groups: (More info?)

    Yep, I sure do. It is the only way I could get the lines to display so
    that you could see the problem. I have adjusted the 50/60hz pot with
    only marginal results. This Defender is only a test bed so that I can
    troubleshoot the chassis. This is a spare tube I keep around to test
    monitor chassis.

    The actual monitor is installed in a TMNT and he definitely has foldover
    problems as the display is upside down in the top 3 inches of the screen.

    I have another picture of the main Defender screen with the "radar
    display" inverted into the main screen. I guess I should have posted
    that one.

    I did try one more voltage regulator with no improvement. How do I get
    the voltages down to where they are supposed to be if the problem isn't
    the voltage regulator? I honestly think the overvoltage is "blooming"
    the picture.


    Ken Layton wrote:
    > You've got the screen control on the flyback turned up too high.
  6. Archived from groups: (More info?)

    Yep, it helps but doesn't completely eliminate the problem.

    Still about 2-3 inches of foldover.


    Arcade_Spirit (Chad Entringer) wrote:
    > Try adjusting the 50/60hz pot. Ive seen this work.
  7. Archived from groups: (More info?)

    Replace the vertical output IC.
  8. Archived from groups: (More info?)

    Yep, that was my next thought. Unfortunately, I don't have one of those
    and will have to see if the local electronics shop has it.

    It is definitely different from the 2 other iterations of Vertical ICs I
    have dealt with before.

    Pat D.

    Ken Layton wrote:
    > Replace the vertical output IC.
  9. Archived from groups: (More info?)

    Yep, that was it. Part N5521 IIRC. Had to make a run to the parts
    house for it.

    Thanks for all the suggestions and help everyone.

    Pat D.

    Ken Layton wrote:
    > Replace the vertical output IC.
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