#61
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I put my glued together ferrite core back in its coil and put the set back together. Then I tried using the Sams IF alignment procedure. It did help some. The Sams procedure tells you to use a demodulator probe at points after the detector. This did not work for me. I used a normal scope probe and got reasonable waveforms. The Sams also shows three IF sweep curves but the alignment text only refers to two of them. After the Sams alignment procedure I did get rid of the ringing in the video but also lost color. I could not match the curves response in the 42-43 MHz range. I used the VA62 multi-burst and tweaked the IF adjustments to get more color signal frequencies through (3 to 4 MHz) and got the color back. But when looking at a channel 3 RF signal I got a noisy picture.
I looked through the R.L. Goodman Zenith Color TV service manual and found a more detailed IF alignment than the Sams. It showed similar sweep curves but its procedure referred to all of them. So my next attempt will be to use this alignment procedure. The procedure is general to cover several Zenith sets, including the 27KC20 (which has very similar design and is the successor to my 29JC20), so some test point designations require translation to use on my set. I am no whiz at aligning sets, but I am determined. Dave |
#62
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Dave |
#63
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I used the R.L. Goodman Zenith Color TV Service Manual IF alignment procedure. It took three iterations but the result matched the sweep diagram pretty well. Here are pictures of the Goodman response curve, the result I got, and the Multiburst response. The alignment got rid of some of the ringing seen on the CRT, but what was left was a dimmer wide repeating pattern. Here is a picture of the video waveform before and after the delay line. I found that the delay line termination potentiometer was open. I opened it and cleaned off the oxidation. I then worked fine, so I put it back in.
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#64
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Here is a picture of the single vertical and horizontal convergence pattern that had so much ringing when I first powered up the set. The color would initially work and then fade away when I first powered on the set after the recap. I found that the second chroma output was fading. It is gain controlled using a bias from the color killer modulated by Zeniths Automatic Color Control. For now I cheated and just put a resistor in parallel with part of the bias filtering to increase the gain to keep the color working. It still kills the color on black and white video and seems to work fine otherwise. Here are some pictures of video through the tuner. I may make one more pass through the IF alignment and then do the audio alignment. The audio has a little distortion in it at the moment.
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#65
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That looks really good !
I'm wondering about the blue dipping on both ends at the edge of the screen..... Could the zip tie around the convergence magnet assembly be changing it's orientation from a perfect perpendicular to cause the dipping....? Imagine if the magnet was forced towards the back of the yoke, and not straight up and down, then if it is trying to make the line straight, but orientation is wrong, pushing the line lower on the ends.... If the magnet's orientation was forced away from the yoke would the line go up at the ends if it's all working correct....? Or am I all wet, and it's most likely a aging part, or the best it's gunna get.... .
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Yes you can call me "Squirrel boy" Last edited by Username1; 02-14-2015 at 09:13 PM. |
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A word of caution: one of those , if you back the slug out too far, will roast one of the pots. So go easy. Last edited by old_coot88; 02-14-2015 at 09:33 PM. |
#67
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Hi !
Not what I was getting at..... On the first page of this thread a picture is posted of the 3 convergence coils held on the neck of the picture tube with the help of a zip tie. I was just wondering if this method changes the orientation of the coil, with respect to the electron gun, and it is either tilted towards the yoke a little, or away from it and results in the downturning of the blue line in the cross pattern on the screen in a posted picture on this page of this thread.... Left most picture post #64. .
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Yes you can call me "Squirrel boy" |
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Dave |
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Sorry there Z I guess I missed a few pages in the middle of your story.....
In #39 you have the assembly removed. A possible fix could be laying it down like you did, put it in as close a position as possible, and tracing out the outside perimeter of it, and making a plastic holder for it - a big circle - with cutouts for the "cloverleaf" and silicon glue the plastic circle to the CL - maybe put shims along the way to get position just right..... Might be more rigid than springs.... and not interfere magnetically..... 1/4" or thicker sheet plastic..... Maybe even polypropylene, or polyethylene.... A little softer, and immune to a lot of stuff..... Give it less brittle start.... .
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Yes you can call me "Squirrel boy" |
Audiokarma |
#71
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#72
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I got better results with another alignment. Here is a picture of the sweep with the marker at 42.75 Mhz and 45.0 Mhz. And a picture of the multiburst showing 0-4.5 Mhz making it through the tuner to the first video amp. This alignment also reduced the ringing of the single vertical line, as shown in the magnified scope image in the fourth picture. The last is what this alignment looks like on the CRT. I think this alignment is a keeper.
Dave Last edited by Zenith6S321; 01-21-2017 at 05:33 PM. |
#73
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I went through the audio alignment which fixed the distortion in the sound and increased the volume a lot.
Neither of the yoke centering adjusting strings would move. I took the yoke off the CRT and was then able to move the strings a little. Working them back and forth a bit seemed to free them up. I put the yoke back on and fired up the set to try to use the centering strings. The strings moved the centering rings but for some reason the image on the CRT does not move. I wonder what I am doing wrong. The image does fill the CRT and the centering is not off by a lot. It still would be nice to get it centered though. Dave |
#74
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Your 29JC is looking good. I have the manual scanned for it I could send you a link to if you don't have it. Just PM Me.
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#75
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I'd be interested in a copy too.
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Tom C. Zenith: The quality stays in EVEN after the name falls off! What I want. --> http://www.videokarma.org/showpost.p...62&postcount=4 |
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