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    Thread: Resetting convergence/purity rings.

    1. #1
      spacies's Avatar
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      Resetting convergence/purity rings.

      I have a tube in the shed and the locking ring is undone and the purity rings are lose. There was no bead of silicone to hold them together and only a couple of pens marks. The markings do not go from top to bottom which is odd.

      Should I ditch it or have a crack?
      BTW the tube is about a year old so I would rather get it going again.

      I have interwebbed this topic and found a couple of good sites but would like opinions 1st.


    2. #2
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      Have a crack. Nothing to lose and a nice picture to gain.

      You'll need a test pattern to get it half-decent. I use 'H's or dots.

      Just watch the HV lead for your own safety.

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      Thanks,

      So I set the colours first then the convergence right? I might give Joey a call. Heh, I rang @ 1pm here while I was eating lunch and his son and he was still asleep. Dam time zones. Bahahahahaaaaaa

    4. #4
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      Quote Originally Posted by spacies View Post
      So I set the colours first then the convergence right?
      It's a dark art.

      COLOR PURITY ADJUSTMENTS

      Screen color purity is normally the first CRT setup adjustment to be made, but it doesn't normally drift very much over time and therefore doesn't require routine adjustment. Purity is said to be good if, when each color is turned on and the other two turned off, the entire screen is all one color. Bad purity will show up as wrong colors on what should be a pure color field, or color blotches on what should be a white screen (all three guns turned on). If you can already get a good white screen, don't fool with the purity adjustments. But, if you must...

      There are internal controls for each CRT "gun" to set the brightness level for that color. To adjust green screen purity (the center gun and the most common one to view during purity setup adjustments), turn down the red and blue guns with their respective controls and/or turn up the green. If you can, somehow mark the position of the controls beforehand so you can put them back when you're finished. Each TV or monitor has it's own terminology for these controls. Some call them "low light", others "screen" or "G2" or "cut off", and still others "bias". These controls need to be reset to their proper points when purity adjustments are completed or the resulting offset "white balance" will show as "tinting" of one color over the entire screen when the brightness is changed.

      An alternate way to do the setup without having to adjust any CRT level controls is with a generator or via a program in the computer feeding the monitor. For example, a simple BASIC program can be written to set forground and background color to GREEN only. Patterns of lines or dots can be likewise generated in a program.

      To adjust purity, set up a green screen as indicated above. Loosen the yoke clamp and pull the yoke back towards the convergence assembly as far as it will go. If there is any glue or tape holding it, it may be necessary to gently twist the yoke to break it loose from the tube. A wide vertical bar of solid green should appear in the center of the screen. If it's off center, the purity rings should be rotated and/or separated to center the green bar. Then slide the yoke forward just enough to get an overall green screen without contamination by red or blue. Use a bar or crosshatch pattern to make sure the yoke is straight (rotational misalignment will cause the picture to be tilted), and then gently tighten the yoke clamp.

      It's a good idea to check the red screen purity, then blue. Slight adjustments of the rings or yoke position may be required to optimize the purity of each of the three color fields. Some compromise may be necessary, but it's usually not important to get it perfect. It has to be pretty far off to show up on a white screen.

      If you turned any of the level controls to do the purity adjustments, reset them to their original spots. The screen should be a neutral grey. To check for proper "grey scale" or "CRT tracking", turn down the brightness control and see if the white screen goes to any color as it darkens. If it does, adjust the level controls a bit to get a neutral grey dark screen.

      CONVERGENCE

      For convergence adjustments, you need to use something to generate a pattern of horizontal and vertical lines on the screen called a "crosshatch". Some techs prefer a pattern of dots. If your source video is from a computer, a screenfull of zeros or + signs will work OK. As stated before, the purity rings are the first set on the convergence stack behind the yoke. Don't adjust those unless you have to. The second pair of rings is used to converge the RED and BLUE lines at the center of the screen.

      Separating the rings will move the beams horizontally (side to side), so for that adjustment, you must look at the vertical lines of the crosshatch to see the effect. Holding and moving both rings together moves the beams vertically. To see that effect, you need to watch the horizontal lines at the center of the screen.

      The third set of rings set the convergence of MAGENTA (RED+BLUE) AND GREEN. AS before, Looking at the center of the screen, separating the rings allows for horizontal beam movement (observe vertical lines) and rotating both rings together moves the beams vertically (observe horizontal lines). All slot-mask picture tubes use a variation of this setup procedure.

      If the center of the screen is properly converged but there is still misconvergence at the screen edges, you must tilt the -front- of the yoke up or down (without loosening the mounting clamp), or side to side for compensation while observing a crosshatch pattern on the screen. Note that up/down movement of the yoke will affect convergence at the screen left and right sides, and side to side movement of the yoke will affect screen edge convergence at the top and bottom of the screen. Smaller tubes don't normally require adjustment, but larger screen sizes can show quite a bit of misconvergence at the edges. When adjustment is optimised, small rubber or plastic wedges are used to hold the yoke in place. Sometimes these blocks fall out. If edge convergence is bad and center convergence is OK, look for loose or missing blocks. They are fitted with double-sided tape or glue to keep them in position between the yoke and the bell of the tube so the yoke can't move. Silicon rubber sealer works well as glue.
      Hope that helps a bit.

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      Jomac is offline
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      Quote Originally Posted by spacies View Post
      Thanks,

      So I set the colours first then the convergence right? I might give Joey a call. Heh, I rang @ 1pm here while I was eating lunch and his son and he was still asleep. Dam time zones. Bahahahahaaaaaa
      Oh yeah we did an all nighter putting pulling a quad motor apart and putting it back in , 4.15am started it up , shit they are loud that time of the morning

      Mate give the tube a go , you should be able to get it fairly close with the marking you have found , if it looks bad you can adjust some of rings and put them back if your not happy with the result.
      Sounds like the rings havent been off so it wont be to bad.

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      Hewitson is offline Arcade Scrap Yard
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      Quote Originally Posted by Jomac View Post
      Oh yeah we did an all nighter putting pulling a quad motor apart and putting it back in , 4.15am started it up , shit they are loud that time of the morning
      Glad I don't live next to you

    7. #7
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