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Thread Tools | Display Modes |
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#1
10-16-2005, 06:47 PM
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Admiral 20A1 problem/was1948 Admiral console cabinet from swap page
I've got a bakelite console that uses a 20A1 chaiss and I've had a problem with getting the picture to center on the screen. With the focus coil angled to the point of being right on the neck of the crt I still have a 1/4 black band down the side of the screen. I'm not sure what the problem is. I did find some bad resistors in the focus circuit and replacing them did help some but It's still not quite right. Any ideas?
Terry 
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#2
10-16-2005, 06:59 PM
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could there maybe be not enough horizontal deflection (weak H.O. tube, damper, low horiz. drive)?
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#3
10-16-2005, 07:25 PM
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>Well all of the caps have been replaced along with a handful of resistors and the >power transformer. Tubes have been tested and the 6BG6 has been swapped just to >doubble check it's operation. Horz sync locks nicely. I've looked at the voltages in the >horz osc and output and all are within 10% of the spec. All in all the set works great >expect for this one issue.
>Adjusting the ion trap doesn't seem to move the picture much however does brighten >it if not set properly. The focus coil T-7 does move the picture but it's skewed all the >way over to one side to try to center the picture. I'm afraid if I adjust it any more I'll >snap the neck on the crt. I don't think It's an issue of the picture not being wide >enough It just won't move over. >A little history. >When I got the set it had spent some time outside in the weather. Chaiss rusted >leaves,sticks,and acorns inside the cabinet. I got it home and started cleaning and >did notice that L-7 was adjusted all the was over to one side. Thought it was a bit >odd and repositions it to it's center position. After working on the set and achiving a >raster I had a 3" band down the right side of the screen. So I went back and >readjusted L-7 so it filled out most of screen. Also some serviceman had changed the >value of R-88 down to 6.8K I replaced it with a 10K but didn't change things much. In >saying all that this set has had the problem for some time. >I was thinking I've got a bad yoke,flyback or maybe crt. but It's got me stumped! The drive seems to be good in that it does change width some but nowhere near enough. The boost voltage is good at the cathode of the damper so I think the 6W4 is ok too. The width of the picture appears to be about right but the position isn't. Terry 7"estatdef View Public Profile Send a private message to 7"estatdef Send email to 7"estatdef Find all posts by 7"estatdef Add 7"estatdef to Your Buddy List
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#4
10-16-2005, 09:33 PM
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Just a SWAG (scientific wild ass guess) suggestion: Maybe there is a missing magnet? Maybe toying with a magnet near the deflection yoke might be enough to move it over. Also, some sets had a C shaped clip with a magnet and spring that would be placed on teh CRT neck (maybe that's the ion trap, been a while since I've fooled in sets this old).
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#5
10-17-2005, 11:10 AM
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If the picture is linear and has enough scan width, then it could be that the horizontal yoke windings have some residual magnetism. Try discharging an electrolytic cap across the horizontal yoke windings. If it moves the wrong way, reverse the electrolytic polarity and try again. Use about 40-60 ufd and a 200-300 volt supply.
Don
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#6
10-19-2005, 08:12 AM
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PROBLEM SOLVED!
It ended up being a bad crt. I poped another 10BP4 in and it work great. As I inspected the neck or the old tube it looks as though the gun is sligthly ouff center. Maybe a bad rebuild job or factory defect. TNX for all of the responds! Terry Onward to the next set!!!!
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