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#1
05-23-2009, 10:42 PM
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dying flyback?
My motorola 21t16 has been good to me so far. Well, today I noticed that the picture was not centered. There is a black bar on the right part of the screen. This set does not have a centering adjustment. I did try the horiz. slug because that will pull the picture either left or right across the screen before it goes out of sync. That did not work.I took it out of the cabinet and put it on its side to check voltages and then lost sound and picture unless I turn the contrast all the way up. If I put the contrast were it was the pic goes black and stays there until I turn up the brightness all the way.I have subbed in all vert. and horiz. tubes and it makes no difference. Is this the flyback dying? The CRT tests good. Thanks, Doug
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#2
05-24-2009, 01:32 AM
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Assuming that the sound and contrast problems were related to the horizontal , not a weak solder joint that was distubed when the chassis was moved .
I would suspect it to be more in the low voltage power supply . Check for a weak rectifier , is it tube or diode ? Are you running selemiums ? Also this could be caused by a weak power resistor . Is the contrast and sound are a seperate issue , I would start in the horizontal circuit , and also check to see that the yoke hasn't slid back a bit . Best of luck with it .
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#3
05-24-2009, 08:05 AM
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I did some checking, the contrast, and sound are tapped of of the video IF after the detector diode. It checked at 5,865ohms resistance one way and 3,880 ohms the other. Well, if I am right that means that it went bad. That still leaves the picture being non-centered.I will put in a new diode later today if I can find one and make sure that a cap that is across the horiz. freq. slug is good. Then I will recheck voltages and see what happens.
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#6
05-24-2009, 08:24 PM
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Yes, that was out of the circuit. I put in a new one but it did not help. I think I might be on to it though, This set has no power transformer, the way it was set up when I got it was incorrect but worked. It should have two seperate power lines. One is to a parallel / series string for tube heaters. the other, dual diodes for a voltage doubler configuration.But in my set the power goes from the off/on switch to a thermal variable resistor then branches to the tubes and the diodes.This seemed to drop the voltage down inorder to compensate for todays higher line voltages. well there is a bad 5w. 120ohm. resistor in the tube line. It reads 3.4 ohms out of the set. I think(hope) that this is pulling down my power from the other line. Some voltage readings were low and they were very close when I first finished this project. I may not be able to get another resistor until tues. so I will keep you posted, Thanks, Doug
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#8
05-30-2009, 06:50 PM
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I put the contrast control in and put the detector diode in the right way and the set is running. Well, I still have the original problem, The picture will not cover the right side of the screen. I did play with the magnet on the crt neck and I can fill the screen but I have to put the brightness all the way up. This problem kind of crept in, it was not instant. The crt still checks good.The voltages in the set are very very close to the diagram. Can the problem be the cap in the Yoke?
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#9
05-30-2009, 06:53 PM
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Before this happened the brightness was about half way up. I also have subbed in different tubes one at a time.I was sure that I would find bad voltages somewhere and since I am not a tech I am really puzzled.
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#10
05-30-2009, 07:07 PM
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It sounds like you don't have enough Horizontal sweep, did you try subbing the damper tube and the Horiz output?
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#11
05-31-2009, 05:02 AM
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Well its good to hear you got the other problems worked out , also another possibility is a resistor is climbing in the horizontal oscillator or output circuit .
How is the brightness , I would imagine that if the flyback was going to die , you would be losing some of the high voltage , and this would cause a decrease in brightness . High voltage and horiziontal probems can be tricky at times because they are both tied into each other . If the voltages on the low voltage supply check out OK them I would start in the horiz osc , check the pots to make sure they are working correctly , and any larger resisitors ine the horiziontal output circuit . If the tubes you had substituted were equivalent to the originals I would not see this as a problem . Best of luck with it .
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#13
05-31-2009, 11:36 AM
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I checked the flyback as far as resistance is concerned, it is fine. The brightness was great and this set had a fine picture until the image on the screen started drifting to the left. I rechecked per your thoughts(tube TV) and found one out of tolerance resistor in the horiz circuit. I missed it the first time, it is hard to see. I will replace it when I find one and see what happens, thanks, Doug
Last edited by radio nut; 05-31-2009 at 11:40 AM. Reason: had to give Tube Tv credit
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#14
05-31-2009, 02:55 PM
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I went to check the pots and I am confused now. The brightness pot per sams should be 5meg. Mine checks end to end 571k. If I put the ohmmeter from pin 1 to 2 and vary the conrtol it starts at 158ohms -goes to 2.486 meg and then back to 550k as I am turning it the same direction. I am used to pots breaking inside and just having no resistance. This I have yet to see. I take it that this pot is bad ?
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#15
05-31-2009, 04:37 PM
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It sounds kind of strange , but if the brightness control works it shouldn't be the cause .
The brightness control is usually in the video output area , some change the grid bias, I forget if it's G1 or G2 in the crt , it should not effect your horizontal .
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