#1
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Split image on Zenith porthole
I have repaired the vertical issues I had with this 24H21 chassis after a complete recap, resistors, etc. John was very generous here and sold me a vertical output transformer that cured my vertical problems, but I have a split image on the screen. If I advance the AGC delay control far enough, I can get it to display a single image but it's virtually invisible (picture quality is next to nil). So, with the AGC delay control in a position that gives the best quality picture and the horizontal hold and linearity controls all adjusted properly, I have the image you see below.
Where should I start looking to correct this condition? Thanks. |
#2
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It appears to be out of Phase, I had a similar problem once but it was caused by a reversed winding on a replacement flyback, in your case maybe it's an issue with the 6AL5 Phase Detector circuit.
That's just a guess, hopefully someone who actually knows something can offer more. |
#3
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My version has the 6H6 alternate for the 6AL5 phase detector. I'll start looking at that circuit, although I have not been able to find any voltages on Sam's, Rider's, or even the original Zenith info for this application.
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#4
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I don't know specifically what is being said to be "out of phase", but I can pretty certainly say that it is a horizontal circuit condition of some sort. Probably the oscillator. Is it locked exactly that way and remains that way? I have had sets where the frequency was so far off that you got a split image, but it was nowhere near as clear an image as that.
The AGC looks too high, but you say that if you bring it down you get a correct, but poor image. Perhaps the AGC needs to be brought down and the video circuits need to be looked into. Just a second thought. As someone else said, perhaps someone with more experience with that type set, or sets in general will pop in with the magic solution. I love it when one of the guys who actually did this for a living lends a hand. B.T.W. I have a repair book, actually tons of them, but one has screen conditions and all of the possibilities for each given condition. If I can locate it I will look it up.
__________________
"Face piles of trials with smiles, for it riles them to believe that you perceive the web they weave, and keep on thinking free" |
#5
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Since its shown no action on the "other" list I will pick
it up here. Good advice given. If you run up the AGC to get a nice sharp pix you can clip off the sync pulse. Usually if to high you also get an audio buzz. If you turn down the AGC & it gives a washed out pix BUT it syncs in go to the video stages. One way to judge things is with NO signal. You should get a nice strong snow with no streaking & a nice waterfall in the audio. If it is a phase problem & not just the 6H6 look at the feedback from the flyback to the phase stage. It looks like the set has a good strong jug & will give a real pissah pix when done. 73 Zeno |
Audiokarma |
#6
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Quote:
to start via the phase stage. Hoz osc being off will give a diagonal line. If way off gives lots of lines or a multiple pix with lines. Here we have a horz osc running normal, it just isnt getting the sync from the source. The pix will float around just like a vert roll. Phase problems were rare in my time ( early 60's sets on) & usually the double diode that replaced the tube or a feedback issue. 73 Zeno |
#7
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The horiz phase detector compares the signal from the synch separator with a feed back pulse from the flyback and if they are not in phase with each other it sends a correction signal to the H oscillator to adjust it's frequency slightly to compensate for that and keep horizontal synch.
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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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