I've been blessed!

[bgadow]

John, you put that RCA in excellent hands! I'm really glad you didn't let it get destroyed like so many others. Great stories, too!

[Tomcomm]

I hope the blue-lateral control's placement in your photo was rotated for illustration purposes only? If not, something is terribly wrong! Is that the one that came with the 21AXP22? I looked thru my junk but I couldn't find one like I have on my 21FBP22. It is directly over the blue gun's lateral pole pieces as illustrated and has a rotation adjustable magnet that provides precise control without any interaction with the red and green screen locations. I hope the photos are useful.....Tom

[old_tv_nut]

Tom, you seem to have a different type of magnet assembly. The one in my picture is supposed to be placed as shown with one end over the internal blue pole piece. When I first got the set, I thought maybe it was accidentally shifted, but no. It is shown this way in both the RCA and SAMS manuals for the CTC-5, and is working properly in this position. I don't think there would be any difference based on changing to a 21FBP22, but there would be a difference if I had the same type of lateral magnet that you do. Steve Dichter sent me a couple of scans from different publications also showing the type I have mounted the same way mine is.

It appears that the end of the cylindrical magnet in mine is broken off, or at least an adjustment knob is broken off. It's still functional, but loose, and that is apparently why it was taped in position.

Edit - thanks for the photos with dimensions - I will compare to what I did.

[Tomcomm]

My wife dragged it home from a garage sale in 1996 for $35. I fixed the remote and got a picture with no ant. Since I had no interest in TVs at the time it just sat disconnected in my office collecting dust. I finally fired it up on a test DVE disc thru a modulator a couple of days ago and got a bright, fine detailed picture with accurate color and near perfect focus! Well that got me interested in learning more about it.

Its a 25in Zenith System 3 made in Springfield, Missouri in April 1986. The CRT is A63AAX02X with a backward cap R sticker which makes it Japanese, right? The screen is stripped like my Sony Trinatron and probably has inline guns. When I took the back off, the CRT has NO convergence assembly like the Sony, just three purity rings stacked together! The yoke has only the usual 4 wires, so no dynamic convergence in here.? The ultor is a single conductor, so no electrodynamic convergence like the Sony Trinatron. I thought the Trnitron was hard to understand but this Zenith thing is spooky!

The plug in assemblies are noted as follows:
Video output 9-467-01
Main module 9-518
SM pwr supply 9-520-02
Tuner 175-2277-01

So what do the Zenith Gurus make of this. Its got 10yrs of main TV use, then retired for 13yrs and still produces a picture as good as any of my analog TVs with the obvious exception of the Sony PVM1334 super-fine pitch pro monitor.

[old_tv_nut]

This is typical of a self-converging yoke/tube design. The basic convergence is done by the yoke design. Touch-up is by tilting the yoke and adjusting permanent magnets. The in-line guns and striped screen mean the purity is not affected by vertical perturbations, so this degree of freedom is available to apply to convergence.

[Tomcomm]

Wayne, thanks for your reply to my misdirected thread message.......Tom

[old_tv_nut]

I borrowed the tool you really need for those brass-screw coils - GC8276, which is a hollow yellow plastic tube with a protruding screwdriver blade on one end (which you don't need) and a recessed screwdriver blade inside the other end (which does the trick). Anyway, I think I have conclusively determined that the core of the H blue amplitude coil is missing, so the chassis will have to come out again. Drat!

[old_tv_nut]

A little update - finally got around to measuring high voltage: 19.8 to 20 kv. Since this is within 2.5% of the value on the schematic (19.5 kv), I think it's OK.

[old_tv_nut]

Not much progress - instead of pulling the chassis to inspect the blue convergence coil, I did some playing with video sweeps, and while in the process. the set developed a horizontal instability that I can't diagnose so far. At first I thought the AGC or tuner might be involved, but I can turn AGC down to a low-contrast picture and the problem remains the same.

Anyway, the horizontal phase became jittery, and occasionally drifts out of sync entirely. I've tried tapping on things and wiggling tubes and wires, and tuning off channel and back, but haven't found anything that causes it. Also tested tubes (although I don't have subsititutes for most), and all in the sync/AGC/horizontal check OK.

Not sensitive to line voltage either. It did seem to clear up by itself for about 30 seconds after warmup when the set had been off for 10 minutes, so I may have to chase some thermal problem.

These old sets do have "personality!"

Any suggestions gratefully received...

[John Folsom]

I would consider replacing all the silver mica caps in the horizontal sync/phase/oscillator circuitry if you have not done so. Try removing each input to the phase detector and see if the oscillator becomes stable again (even if it is not being synchronized). Another possibility is a carbon resistor that has begun to behave badly. I have seen resistors give some funny symptoms.

[old_tv_nut]

When I get the chassis out, I will make some resistance checks.

Assuming the problem is caps, though, do you recommend replacing silver micas with silver micas, or with ceramics?

[John Folsom]

Silver micas for silver micas. I am not smart enough to figure out which ones could accept a ceramic cap. And silver micas are still readily available, and not expensive.

[roundscreen]

Originally Posted by old_tv_nut

Not much progress - instead of pulling the chassis to inspect the blue convergence coil, I did some playing with video sweeps, and while in the process. the set developed a horizontal instability that I can't diagnose so far. At first I thought the AGC or tuner might be involved, but I can turn AGC down to a low-contrast picture and the problem remains the same.

Anyway, the horizontal phase became jittery, and occasionally drifts out of sync entirely. I've tried tapping on things and wiggling tubes and wires, and tuning off channel and back, but haven't found anything that causes it. Also tested tubes (although I don't have subsititutes for most), and all in the sync/AGC/horizontal check OK.

Not sensitive to line voltage either. It did seem to clear up by itself for about 30 seconds after warmup when the set had been off for 10 minutes, so I may have to chase some thermal problem.

These old sets do have "personality!"

Any suggestions gratefully received...

One other thing you should check is the grounds on the board. I have seen grounds cause all sorts of problems and the best way to cure them is hard wire the grounds to the metal chassis. Heat from the tubes and such will cause the boards to warp. Man,You have done a lot of work on that set and it looks nice.
Ed

[wa2ise]

Originally Posted by old_tv_nut

Assuming the problem is caps, though, do you recommend replacing silver micas with silver micas, or with ceramics?

Don't use ceramics, they drift too much with temperature. Else you'll be forever twiddling with the horiz hold knob.

[old_tv_nut]

Thanks - I wasn't sure if NP0 ceramics might be preferred. I'll just stick with micas.