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#31
08-28-2008, 04:11 PM
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RCA, in the early 80's, was using, in production, a kind of magnetic tape that was formed in a ring around the CRT neck. In the factory, they would adjust various magnetic fields thru this tape ring, to do convergence. Once the factory worker felt that this convergence was good, on this particular CRT, the production machine making the convergence fields would "record" these magnetic fields into this magnetic tape, like a tape recorder does to imprint the desired magnetic fields onto tape.
Field repairs would require that the TV repairman throw away this piece of tape, and install a thing that had several adjustable magnetic rings, and adjust them to get convergence. repairs like replacing the yoke, or the CRT. Don't know if RCA was using the above magnetic tape scheme in 1978.
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#32
08-28-2008, 04:40 PM
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I've never had the need to remove the tape on these CRT's. By the late '80's, RCA CRT's featured bonded yokes which means the whole CRT, yoke, and convergence magnet is changed as a unit. Sure beats having to set the purity and convergence. The downside is that if the yoke fails; you have to change the CRT unless you can figure out how to un-bond the original yoke. Fortunately, I've never seen a bad yoke on the bonded RCA tubes.
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#34
08-29-2008, 09:09 AM
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#35
09-01-2008, 12:28 AM
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Okay, I've discovered some things about the complex convergence setup on this TV:
The 3 color gun positioning controls also affect purity. Assuming that all 3 must be adjusted for best purity, I have done that. There are two sets of ring magnets on the back of the CRT: The set closest to the back seems to control the screen centering. The other set seems to help control the blue convergence.
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#36
09-01-2008, 12:05 PM
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the rings are for purity.it must be set first.use a red only screen for this adjustment.the 3 controls on the crt neck are for center convergance only.the smaller controls are for top.bottom,left side,right side.etc.steps are as follows-
1.-red screen -purity 2.gray scale-service line,adjust rgb to a white line,even luminance. 3.center convergance-red and green,blue vertical and horizontal(dial on purity assembly) 4.top -small controls-marked-red,green,blue 5. bottom-same 6.left side-same 7.right side-same once purity is set and center is aligned,it should be close enough for viewing.no reason why a delta gun cant be near perfect with some tweaking.dont drive yourself insane trying get it perfect-not going to happen.it can be very close and deliver a fine picture. use an alignment tool(diddle stick) for the sides.i have an xl100 from 1974 and it came out very well. good luck!
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#38
09-01-2008, 05:52 PM
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if this is a delta gun-then,yes,the rings are for purity. 2 rings nearest the yoke will be for best red purity.adjustment will move the picture off center.the other set will be your blue lateral (horizontal).use red screen(turn blue and green controls off) and move the first rings for best purity. if red screen is not attained,then you have to degauss or reposition yoke. adjust screen to white line in service position.then use the 3 controls on the neck of crt to converge center. this should give you good purity and center. adjust smaller controls as needed and they are marked as to what they control.i worked as a young man in a repair shop and my main job was to repair tuners and set up convergence.i have worked on that colortrak series before.i owned more than a few of those great sets.use procedure as i posted before.sometimes those old pots get screwy with age and those will really throw your alignment off.the procedure to set up a delta gun didn t changed much in the 25-35 years in production.crt number is a delta gun 25 inch full viewing.should be a great performer for you.
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#39
09-01-2008, 11:03 PM
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Well, Misfortune has struck again.
Most of the controls on the TV are plastic knobs that I can turn by hand. However, a few adjustments are coils that I've been using a small allen wrench to turn (turn it, remove wrench, reinsert wrench and turn somemore, remove it, and repeat.) Anyway, I BROKE one of the coil slugs and it's stuck in there! I'm going to try removing it with a screw that has some glue on the end. My hope is that the glue bonds and I can just twist it out. if not, then I'll have to replace the entire coil, but where do I find a 30 year old coil?!
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#41
09-01-2008, 11:28 PM
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what roundie do you have? i have lots of rca coils.you are welcome if you need something.
mrx37-a broken slug is no big deal.set everything else and maybe you are good enough without the hassle.you can desolder coil and take it out fro the bottom side,resolder into circuit and reinstall another slug. i have broken millions of those things.not a big deal. it cant be that far off unless you broke the coil.good luck
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#42
09-01-2008, 11:41 PM
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Where it's at right now makes the red and green impossible to converge on one side of the screen. I'm going to try removing the slug and replacing it, assuming I have a similar sized slug.
Failing that, I'll need to find a 30 year old coil... EDIT: My glue trick worked! Got the old slug out, and am hunting around for a new one!
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#43
09-02-2008, 12:47 AM
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Okay, here's my substitute for the broken slug, tell me if it's a great or a stupid idea:
I found a steel bolt that is of the same diameter and threading as the slug. I put it in and it seems to work fine. I also found a diddle stick that actually fits the other coils too!
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#44
09-02-2008, 01:19 AM
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 It may be a bit lossy, but if the set appears to converge fine, then I'd leave it, unless you have a huge piece of it sticking out, flapping around enough that you think it might bust the coil off the board. Most any ferrite core with the right threads will probably work. Old IF transformer coils and such stolen from something in your "junk box" (we all accumulate a fair amount of scrap electronics we keep around just for reasons like this).
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#45
09-02-2008, 09:24 AM
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24nc31
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