Fixing Zenith CCII Avante 25JC49

[Alex KL-1]

A little though of this curious subject...
Maybe, depending on the model, it are outputting audible tones with ultrasonic hardware, when it emits 2 ultrasonic tones (2-tone mode, but I dunno about models using this scheme), and it intermodulate. 8kHz audible can for eg. significate a 30kHz and 38kHz making a IMD difference tone.

[drwatson32]

Quick question- are the plastic coils for the convergence supposed to run hot? I was trying to get some adjustments made, probably had the set running for an hour. Noticed the slightest amount of smoke coming from the area of the L601 convergence coil (for blue horizontal lines on the left side of screen). I shut the set off and found the surface to be 145F with an optical thermometer.

The coil below it, L603, was seized up, but it seems that the heat from operating has freed it up, so I guess that's nice.

I feel like I am at least making some headway, getting an idea for how the pots correspond with the grid on screen. Purity is out of whack now, so I have to circle back to that, but at least I'm a little less jumpy around this thing. Once every once in a while, I head an arc or two snap when powering the set on. I'm still trying to figure out where that could be. It's pretty quiet in operation. Actually, the CRT doesn't seem to whine like it used to when I put a grid or dot pattern on the display. Would a new tripler be why?

Also, how are these ECG triplers? Are the failure rates similar to original?

[drwatson32]

Back! 2 days after my last post, my second daughter was born. I'm starting to find the odd moment here and there to circle back to this. At least through a facebook tv repair group, the general consensus was that the convergence coils run hot.

What I'm trying to do now is to set up the color purity. This looks so easy on youtube videos of 1960's delta tvs, but holy cow, things are cramped on this vertical chassis! I'm only able to move the deflection yoke about half an inch forward or back, so I'm not getting a great view of what exactly is going on when I move one ring or the other. Any pointers here? (like does one ring move the spot up and down vs left and right) I can get the red region mostly into the middle of the screen, but it's not a nice round spot. When I push the deflection yoke in, I'll still be left with a little green or blue in a corner. SAMs photofact doesn't dive into this much. Thanks!

[Electronic M]

Purity rings behave the same as centering rings on a monochrome TV...If there's only one tab on each ring then when the rings overlap they cancel each other out and at maximum spread have maximum shift in one direction that you can rotate by moving both rings at once in the same direction.

If you can get a service degaussing coil or make one from a scrap BPC TV (as I have a sticky on somewhere here) it's a good idea to manually degauss before going through the purity process as sometimes the screen can get magnetized bad enough that the internal degausser isn't sufficient.

If yoke travel is limited and you can't get good red spot, adjust for best centered red you can slide yoke forward until the screen isn't underscanned and you find the spot with minimum impurity (it doesn't need to be maximum forward in operation), then if necessary tweak rings to eliminate or minimize impurity.
I've had at least couple of sets where yoke travel made the by-the-book purity adjustment process impossible (was able to get through it by feel and screen educated guess work)...If there's bad enough screen magnetization you'll never get it perfect or have a very long manual degauss ahead of you...Some sets only need a degaussing.

BTW you can undo some angle braces at the sides and hinge the chassis down and away from the CRT to get better access if necessary.

[drwatson32]

Very informative, thank you! I have things closer yet, but not still not great. Best result, with no underscan even, seems to be with the yoke mostly pulled back. Everything goes way out of whack when moved forward. I'll aim to get hold of a degauss coil before really beating myself up on this further.

Side note- the purity ring/blue lateral magnet setup on this set is so weird, rings are inconveniently behind the magnet, very hard to get hands on. I'm about 99% sure it's not on backwards either. The magnet adjuster faces forward.

[vol.2]

Originally Posted by drwatson32

Very informative, thank you! I have things closer yet, but not still not great. Best result, with no underscan even, seems to be with the yoke mostly pulled back. Everything goes way out of whack when moved forward. I'll aim to get hold of a degauss coil before really beating myself up on this further.

Side note- the purity ring/blue lateral magnet setup on this set is so weird, rings are inconveniently behind the magnet, very hard to get hands on. I'm about 99% sure it's not on backwards either. The magnet adjuster faces forward.

I don't know what that TV is supposed to look like inside, but it almost seems like that's on upside-down, not backwards. You'd be able to grab the rings if the magnets were facing down.

Hopefully someone (Zeno?) can comment on it.

[drwatson32]

The job and kid situation has really been making hobby time near impossible to find! However, I've been motivated to really come back to this and make headway since I restored a mid-80's linear stereo VCR in the meantime. I got the color purity set pretty good a few months ago, and then started trying for convergence just recently. I feel like I have a handle on the process- going the rotation of steps in the SAMS, touching up the center as necessary. However, I'm just not getting there. This isn't a matter of trying for perfection, it's just that there doesn't seem to be enough adjustment to converge reds and greens anywhere close to decent at the top/bottom/sides.





Today, I decided to pull the convergence neck board out and start checking components. I desoldered all of the pots and checked them. They all seem pretty good. 2 of the 300 ohm ones only go up to 290ohm at either end, but nothing seemed to be a failed part. They all did influence things on-screen. (as did the 3 transformers) I mounted them back up and that's essentially there I'm at now.

I DID see that a maybe 1/2w 330ohm resistor looks to have gotten hot, making it a little hard to identify the colors, It's measuring 390ohm in circuit. Maybe that's a sign that I should consider replacing all the presumably carbon comp resistors on the board. The SAMS is missing the resistor list, guess that'd have been too easy, but I should be able to do my homework and ID them.

Is there anything else on the board, or otherwise, that I should be looking at that could be making it impossible to get moderately close to good convergence? Thanks for reading along!

[Electronic M]

If the convergence diodes are all in a milti-pin module they're probably selenium and could be bad. Also if the convergence yoke isn't lined up right on the neck that can cause issues.

[drwatson32]

Thanks! It looks like I've got 13 discrete diodes all over the convergence board. I'll have to lift an end of each to check them out, on the to-do list while I have the board removed.

[vol.2]

My first thought was also the yoke. I've had convergence issues that turned out to be purity issues and vice versa.

Assuming all your diodes are checking okay and nothing it obviously wrong, you probably want to start from square one and reseat the yoke etc with best purity and everything in the middle

[drwatson32]

That could be, the purity adjustment wasn't fun and maybe not 100% perfect, I'd call it 99%. Not only did the yoke not move enough to get to where I could see where the red spot (in it's entirety) was, but the lateral magnet/purity ring assembly is either a weird design that puts the rings behind the magnet, or it was installed backwards. I do wonder if it can be turned around so that the rings are easily accessed. Of course, that would put the clamp up near the convergence magnets. I used a permanent marker to indicate exactly where this was positioned, but I could imagine having to circle back to fixing purity when reassembled, anyway.

This is the side that has been facing out:


The rings are tucked behind. I haven't seen another CCII photo with this particular assembly. The grainy pic in the SAMS seems like it *might* be the same, though.

[drwatson32]

Good evening! I ended up checking all of the diodes and replaced all of the carbon comp resistors. Upon reassembly, I found that some of the adjustments for red and green magnets were no longer working. I removed all 3 magnets and found that the red and the green each had an open coil. The connections looked to be corroded. I was able to fix both sorry looking ends of the bad red coil. Sadly the green magnet is now FUBAR. (I actually managed to solder if but broke it when snipping off excess wire. bummer)

Does anyone happen to have any of these from a neck board kicking around? Numbers on the magnet are S-94731 273S7722

[vol.2]

Originally Posted by drwatson32

Sadly the green magnet is now FUBAR. (I actually managed to solder if but broke it when snipping off excess wire. bummer)

I have seen people just replace the ends of the wire with new wire. As long as you don't alter the number of turns a great deal, they should still work within adjustment range.

I do know what FUBAR means, but perhaps you can peel the onion back a little more than you thought you could, and try to solder a new wire onto the ends.

[drwatson32]

Originally Posted by vol.2

I have seen people just replace the ends of the wire with new wire. As long as you don't alter the number of turns a great deal, they should still work within adjustment range.

I do know what FUBAR means, but perhaps you can peel the onion back a little more than you thought you could, and try to solder a new wire onto the ends.

Aye, that's where we ended up once I carefully unraveled it a bit, trying in vain to find the new end. It became a mess, unfortunately.

I am looking forward to trying adjustments again once I find a donor- I've only had particularly good luck with moving blue around, and now that makes a bit more sense.

[Electronic M]

I've dismantled a few upright CCIIs as CRT donors for older sets. I probably have a compatible convergence assembly at home. Not sure I have time to dig one up tonight with 2 oil changes and some other chores that need doing.

Your set doesn't have Zoom correct? (I know zoom sets has a more complicated deflection yoke and possibly convergence too) I haven't parted out any zoom sets.