got this yesterday off a CL list.

brought up slow with HOT pulled, no excessive current caps stayed cool, so tried it with the HOT in. Raster, hook up a converter, picture.

Issues

with the AFC switch on the color does not sync up, rather bars roll thru the pic, AFC off and its fine.

Red is weak, not sure how to adj purity on this, I could not see the rings like on the RCA. It has what looks like trim pots built into the convergence assy.

CRT has a brightner on it. I checked it (with out the brightner on a sencor CR-70, green and blue were just in the green zone, red is about the middle of the red zone.

Focus is not good, it is at the extreme end of the adj and its still not very sharp.

odd thing, it seems to have a uhf tuner (has ant feed in wires and a small coax going to the vhf tuner, but I can't for the life of me find a display for uhf, it has a single tuner knob, and no place showing uhf numbers.

anyone have a service manual they can share (scan) with me?

Before I dig into it I figure I should start checking voltages, esp on the focus.

the HV looks good its at about 24kV

I will get some pics as soon as I find the camera...

oh one last thing, anyone have exp with the sencore CR-70 restore/rejuv functions? I was just wondering if I should give it a shot on the red gun.

Does it have the concentric tuner? After channel 13, a white window should appear and then you adjust the outter knob thats used for fine tuning VHF as the UHF tuner. A smaller diameter drum is inside the VHF indicator drum that has the UHF channel numbers on it. They can be hard to turn though, Ive seen these tuners with stripped teeth on the UHF dial drum when someone forces the tuner when its stuck.
No color sync with AFC on? How is color sync if you offtune the set with AFC off? AFC module may be out of alignment, which is an easy to correct. however, First thing is to check all those tubes and be sure you use a tester that can test for grid emission. So many people use testers that don't test grid emission and a bad tube slips by every time causing problems. The 6JU8 color AFC is a common suspect for color sync issues though.
Poor CRT may=poor focus, however its common to find a zenith with focus that won't come in sharp enough. A brightener on a CRT is basically a death sentance to the tube (kind of like "instant on"). Open up the HV cage and replace the 212-85 selenium focus rectifier. Replaceing that will bring the focus back and the control won't be at the end of its range. Its soldered in, its brown in color about 2.5" long on the right side of the flyback board. The correct replacement is an NTE-118, you might have to shop around the internet to find one as I dont think NTE makes them anymore. Moyer of course would be the best bet to find one.

replaced the 6EM8's 6KT8, 6EU8, 6EC6 ( I think that was it) basicly if all the tubes that seemed to have color assoc with them, prob not needed but the color sync is fine now with AFC on.

I will check out that focus rectifer.

Yea I was bummed out when I saw the brightner :(

I will have to be on the prowl for a replacment or maybe a hawkeye rebuild.

its got some cataract as well, not real bad but there.

I found the purity tabs don't know how I missed them before.

The weak red is hard to adj out, if I turn the blue and green down and red up I can get a decent picture at one seting of the color, but if I adj the color from the front of the set, then the mix is all wrong again.

what you said about the tuner make sence, there is a un marked segment between 2 and 13 I will have to go back and check that out. Not that I plan to use the UHF, mostly I plan to drive channel 3 with a rf modulator.

your were right about that tuner, a closer look and I could see the uhf thru the window (kinda foggy, so I missed it at 1st).

The tuner is real flakey, feels loosey goosey and needs to be jiggled to get a good pic.

The UHF is hopelessly frozen, so at some point in the resto I will need to pull it out and see what the problem is. I assume just lack of lube and possible corrosion.

I am on the hunt for a CRT "may" have a lead on a local donor set, real ugly looking monstrosity that I would not mind using the CRT from. but have to get a closer look to see if the CRT is correct and test well 1st.

000

found a tube for it at VDC, I was concerned about hitting it with the rejuve, but with a replacement I will give it a go.

I figured if someone had hung a brightner on it some time ago, then the rejuve had been tried and did not work.

vdc make a great tube.i have a 21 round that really puts out the picture.smack that zenith on the soft stting.they will respond well.if you are going to change it anyway?i have NEW 23V SYLVANIA CRT,if only you were closer.good luck and that is the same chassis i picked up yesterday.

yep will do, think I will hit it, just for grins, having a replacement on the way makes me feel beter about it.

next up will be a HOT/Damp/Rectifier to see if that helps the focus (thx charlie!) and a new Se boost rectifier (saw one around here somewhere, just have to find it).

I was feeling a little down about the crt, but the prospect of a new one makes me feel a whole lot better about the project.

oh and the chassis looks to be easy to work on, I spied a few caps that will be checked brown plastic (pretty sure they are paper in plastic cases), a ceramic tube wax ended .1 1000vdc a couple like that, and some small electros, 100uf think its a bypass cap for a osc, and a couple other cardboard wrapped electros that in my exp tend to be open. All easy to get at.

Can't really see the fly since its covered by the mounting board. I will need to check the cathode current, after ai locate a sams. will try my local buddy for that, if not will need to get a service man. I assume I could just check the HOT cathode current and if its around 200ma good to go?

got the boost voltage rectifier, but no sams today. I think I recall someone saying they may have that one. If possible please scan me a copy.

I am going to replace that boost rec and try again for better focus.

I think I may try it with the brightner off, and then rejuvneate the red gun with the Sencore CR 70.

got a good 6LF6 to use in place of the 6JS6C. The tube list said a 6LF6 or a
6LB6, but not listed a 6JS6C. I dont know my tubes that well, perhaps the
6JS6C was a valid sub. Anyway I will recheck the cathode current after I make the switch. The damper and regulator checked out ok.

Was the jumper lead next to the horizontal output changed to the "6LB6" position? The 6LB6 runs at a higher plate voltage.

Was the jumper lead next to the horizontal output changed to the "6LF6" position? The 6LF6 runs at a higher plate voltage. Also, 6JS6C is fine as the suffix letter means the tube has a revised design but still meets parameters of the original design, so its still the same tube.

not sure where the jumper is, I will go back and have a look.

Got the new boost rectifier in, MUCH better, focus is excellant and no longer at the end of the control.

Still weak in the red, will be trying the rejuv soon.

Going to double check the HV and the cathode current (this time with an analog meter, an old simpson).

Sucess!

I used the auto restore mode, the red gun came up and is much closer to the others. I did not understand the tracking control very well will have to re read that, but for now the CRT is looking pretty darn good (have convergence issues on the sides, but I dont want to tackle that with out a Sams or service manual).

Of course as with Klatu, no way of telling how long the restore will last.

Doug, the jumper is in the aft most postion (closest to the back of the chassis). there was some paper there, but it is torn and I cant tell which jumper setting is correct. I can see ther two arrows printed on the paper but the tear is such that it does not tell which arrow is correct.

The KV is about 27, there is a warning about not going over 25. think it could be set wrong?

I assume the cathode current is checked in the normal manner (on the HOT) for current, that is lift the connection and read with a .47 bypass cap in P with the meter leads. Can you tell me the spec current range?

hopefully this CRT will last and I will be able to just hang on to that 23VEP22 as a spare.

Going over the schematic, a few questions

there are some transistors I am just wanting to make sure I know what I may need, but the cross to the zenith part number comes up with various possible choices. Looks like a NTE 107 would do for all if I am reading that right. or is a rat shack equivalant unit available? its a NPN silicon, used in UHF tuner, video amp and the AFC buffer amp. the UHF tuner is jammed up, so I dont know if it is working, the AFC seems a little flaky but that may be the slide slide switch, and the video seems ok but I need to check what I think is a decoupling cap (C3 50uf) on the collector. getting some kind of interference in the video.

I assume you used the NTE cross reference thats on the web? The 121-587 which I believe is a video driver in that chassis is replaced with an NTE-123AP. In fact, I think the 123AP replaces many of the different types all together. Not sure what you would use from radio hack though.
Intermittent AFC is most always caused by the switch. Give it a spritz with some contact cleaner and troubles should be over.
All tubes are tested and good? Intermittent video problems/interference? Alot of times those IF tubes have intermittent contact in the sockets and can cause flashing and odd syptoms on the screen.
Cathode current should be under 200mA. Once you find the lowest setting, turn the core into the coil 3-4mA above that point.

I will try the cleaner on the switch. It's also kinda stiff, so I am guessing some corrosion in there.

I did use the transistor sub from NTE, using the sams listed GE-12 part number. I did not even think to look at the actual transistor, duh.

Stiff tuner is a problem in early production concentric tuners. The 1968 models used an all plastic VHF channel drum, which has a tapered plastic shaft as part of the mold in the center. The UHF drum is also plastic and fits into the VHF drum. The plastic basically deforms, either the UHF drum shrinks, or the VHF drum shaft expands causing the two to lock up. Lubrication will not cure it. You will need to take it apart and use emrey paper to sand the tapered shaft on the VHF tuner. You are only removing a few thousandths of an inch of plastic, just enough to make the drums able to turn freely again. You want no stress on the dial, it should spin free before you put it back together. You will also notice that you will need to add an additional washer to gain clearance between the VHF and UHF drum as the spring tension on the top of the UHF tuner caused enough stress in the center of the VHF drum which ends up deforming the VHF drum. This then caused the tuner to no longer contact the thrust washer in the center and the outside edge of the UHF drum would then come in contact with the VHF drum, causing additional drag (and wear).
Its certainly not the best tuner design around, Zenith could have done much better. I've taken many of them apart, so I am very critical of the design. However, By 1969, Zenith must have realized the design problem (considering an improvement was made only 1 year later, most likely caused by heat from the tubes causing deformation to the plastic components) as they incorporated a brass sleeve insert for inside the UHF drum. This solved the stuck tuner drum problem, but the spring tension on top still caused the VHF drum to felx enough to still contact the OD of the UHF drum. That alone still caused enough drag to make the tuner difficult to operate.
It might sound more complex than it really is, you will see it all when you take it apart.

You nailed it Doug, your trick worked wonders on the set we talked about last year. It works like a charm still :thmbsp: It's funny how that shaft seems to swell up and seize, or the drum? Either way it's weird, maybe the plastic starts to break down over time and warp. I've seen old plastic do funny things LOL.

roger all that Doug. I have kind of put it on the back burner for a bit, got to get the shop picked up, get ready for holidays etc...

I will prob send in the tuner for a rebuild after I get it all out and deal with the stuck UHF.

I still need to replace the caps and take a shot at the purity/convergence (the convergence is off). And of course I still plan to add that HOT cathode fuse.

Anyway back to the shop....