1951 Zenith 16" Porthole

[John Marinello]

Well, you could do what the old-timers used to do... pull the anode & see how
much of an arc you can pull... About an inch, you should be fine.

[Radiotronman]

I ordered the remaining caps I needed to finish the recap, so I can move forward and address any low hv issues.

[Radiotronman]

A friend gave me another 16gp4 to put in this set and now I have a nice bright raster. I have sync issues to fix, but most importantly the left side of the screen is dim. Anyone know what is causing this. The ion trap in its current position is its brightest place. I can get a picture in the left side, but obviously night as bright as the right. Any thoughts?

[Radiotronman]

Is the set with video.

[EdKozk2]

Originally Posted by Radiotronman

A friend gave me another 16gp4 to put in this set and now I have a nice bright raster. I have sync issues to fix, but most importantly the left side of the screen is dim. Anyone know what is causing this. The ion trap in its current position is its brightest place. I can get a picture in the left side, but obviously night as bright as the right. Any thoughts?

I may be wrong, but one time I got an image like yours and it was because I had the ion trap and focus coil/ magnet in the wrong place with respect to each other. It could also be AC getting into the DC at the CRT. Reminds me of old time video scrambling. Did you finish the recap?
Ed

[Radiotronman]

Yes, I finished the recap. Not sure what to make of it or to do. This set us so close to being done.

[bandersen]

Ion trap magnet could be weak or flipped around backwards.

[Electronic M]

Part of me wonders if the door knob cap might be open.

[Radiotronman]

I've tried multiple ion traps and flipped them around and no change. Could it be a bad door knob cap? I've never seen a bad one.

[Electronic M]

I've heard of them shorting, but can't recall an open one. To me it looks like either the gun drive or the HV is varying across each horizontal line (which could be caused by an open door knob)...That or it is an electron optics problem, but you've checked the trap, and there does not seem to be a focus coil IIRC, so varying voltages seem more plausible.

[John Marinello]

Originally Posted by Radiotronman

A friend gave me another 16gp4 to put in this set and now I have a nice bright raster. I have sync issues to fix, but most importantly the left side of the screen is dim. Anyone know what is causing this. The ion trap in its current position is its brightest place. I can get a picture in the left side, but obviously night as bright as the right. Any thoughts?

Try adjusting the centering control... it's that tab thingy between the focus coil
and the yoke.

[Radiotronman]

I tried that control too and it didn't correct the issue. Good thought but I already tried it...thanks.

[Electronic M]

If the set is focused properly currently and moving the coil does nothing, I'd like to know if adjusting the focus control away from proper focus changes how much of the picture is dark.

[Radiotronman]

Adjusting the set out of focus made the picture less sharp, as expected it would. But didn't do anything to help brighten the left side of the screen.

[Eric H]

I had this same problem with a Predicta Holiday, I don't recall what it was but it wasn't a mechanical issue, something getting into the video and blanking it on the left side I think

Try rotating the yoke and see if the problem follows it, if it does that would suggest it's in the video.