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Discussion Starter · #1 ·
I made a post a month or so ago about having lost the green focus on my NEC 6PG. I received some input from forum members, but my projector is still broken and I am looking for new ideas. Is it possible that the STK chip I replaced was bad to start with? Are than any new ideas as to what I might try to fix it. Here is a link to a convergence screen shot and picture of my F-Drive. Thanks for any help.
http://members.cox.net/wschellen/
 

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You tried the the middle POT locted at the back of the deflection board next the Blue Defocus switch
 

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Change the FR and FG connectors around and see if the problem moves. If it does not, check the astig magnets. If it does move to the red tube, you still have a problem on that board.


Let us know.


Marc
 

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Discussion Starter · #4 ·
Yes I tried the POT on the deflection board. No luck.


Marc,

I changed the FR and FG connectors as you suggested. The problem stayed with the green tube. I put the connectors back and tried the astig magnet adjustment rings. These rings definitely make a difference, but the range of adjustment is not enough to bring the green into focus. It is interesting to note that only the vertical green lines are fat and out of focus. This is visible in the photo I took. Thanks for the help and let me know if you have further suggestions. Thanks


Will
 

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Hmmm...... Looks like the F-drive is ok, then.

Are all the magnetics in the right place? The green should look like the red, as far as all the parts go. You may have a bad focus coil. Put up a dot pattern. Put the electronic focus to 0 in the focus menu. Store that. Now does the focus pot make any difference when you turn it? Check the astig magnets to make a round dot, btw. Try turning the focus coil around the tube to change focus. If the pot on the def. board does nothing, you MIGHT have a bad coil. Plug the red coil into the green and check that the electric focus works.

If it does, I think you are down to the coil.


Marc
 

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Discussion Starter · #6 ·
The parts all seem to be in place, the green looks like the red. When you say adjust the focus pot, are you refering to the little pot on the def. board or the adjustment knob in the white box mounted to the side of the case? As for the focus coil I am not familiar with that part, sorry I am just a hack who is not afraid to try. Point me in the right direction and I will give it a try. Thanks


Will
 

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Hi Will,

The deflection yoke which is located at the neck of the tube , it is a grey cylinder that contains the coils and has raster centerings rings connected to it). The whole assembly, which we sometimes twist to get the the horizatal line of the cross-hair of a tube level during a mechanical setup, also slides on the the tube.

First you need to loosen the screw that looks like a dip stick, it holds the deflection yoke in place, and slide the deflection yolk towards the the front of the tube( you can also side it back to see if it helps). Then tighten the screw, do not over tighten.


Hope this helps, because this also affects focus.

clopez
 

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Discussion Starter · #8 ·
Clopez,

Thank you for the input, but it is not clear to me what you are telling me to do. Is the focus coil the plastic ring that plugs into the F-Drive? Are you saying I should loosen it and then slide it forward toward the front of the tube? Thanks.


Will
 

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The focus pot on the deflection board is the 3 pots in the corner right next to the defocus switch. The pot in the middle of the 3 is the green focus. It's safe to turn it, see what it does. Obviously the other 2 are red and blue focus.


Marc
 

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Discussion Starter · #11 ·
Hey Guys,

I am back at it and here is the story. I loosened the focus coil and by sliding it all the way up the neck toward the front of the projector I can make my green lines look good again. Also I checked the green focus pot on the def board and it does make a slight change to the focus when I adjust it. So what does this mean? Is this a sign of some type of wear on the green tube? There is no way the focus coil could have moved that far on its own. Is it ok to run the projector with this coil pushed all the way forward? You guys have been great. Thanks alot.


Will
 

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Hi Will,

Do not turn the focus pots indescriminately to get the center dots focused. It affects your outer focus as well. so if your astig calibrations are incorrect you can end up with a focused center and an out of focus edge.



Anyway I am happy to see thing work out,


Back to my hibernation


clopez
 

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Discussion Starter · #13 ·
Clopez,

As I slide the focus coil forward to thin out the grid lines it also rotates the entire grid clockwise. It appears that I am going to have a hard time getting the lines both focused and square at the same time. Is there a trick to this? Do you know why I suddelny need to slide the coil forward to have it look good? Don't go into hibernation yet, I need you. Thanks


Will
 

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Will, before you get frustrated, remember that everything affects everything else. Look at your RED tube. Duplicate the position of the magnetics on the green. Also the angle at which the wires come out of the focus coil. Start there. I asked you to turn the green focus pot to see if your F-drive and coil are working properly. It is possible that your astig magnets are so far out of whack that you are trying the wrong approach. It's hard to help by typing, without getting a base reference. So please first exactly duplicate the red setup and positioning of the various coils. Mechanically this is usually correct, and then we can go from there. You probably will need to do astig at some point anyway. Astig greatly affects focus.


Marc
 

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Discussion Starter · #15 ·
Ok that makes sense and I will try it tonight. What I cant understand is how something mechanical would have gotten so far out to begin with. I had this projector mounted for about a year and all was fine until the day I turned it on and noticed the green was all smeared. Dont get me wrong I will be happy to have it fixed, I am just curious I guess. I will look at the red tube tonight and duplicate the astig and coil alignment. Thanks


Will
 

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Yes Clopez, I am going on the premise that the red is still in focus. I think the F-drive may still be bad. But I am looking for a starting point to troubleshoot with.


Marc
 

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Will, I also have a spare F-drive board, if it turns out yours is still bad.


Marc
 

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Marc,

I would agree that the F-drive board may still be bad, especially since Will made so much mod.


However, what is the correct distance, or factory setting, between the focus coil and the tube neck (or back of tube).


Thanks,

clopez
 

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Point taken. The deflection yoke should be snug up against the CRT. The focus coil should be approx 5/8 inch from the joke. Measure the GLASS gap between the 2 elements. The astig rings have approx 3/8th inch gap between them and the focus coil. Again, measure the GLASS gap. Minute adjustments can be made, but that's for serious tweaking and attention to detail.


Marc
 
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