Split image on Zenith porthole

[TubularTVbob]

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.

[Eric H]

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.

[TubularTVbob]

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.

[Tubejunke]

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.

[zeno]

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

[zeno]

Originally Posted by Tubejunke

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.

The sync separator passes along a pulse to tell the horz osc when
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

[Electronic M]

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.