View Full Version : I might be getting a 1968 Zenith color!


TUD1
01-23-2017, 07:09 PM
My friend that lives near me in Birmingham went down to Louisiana yesterday and picked up a 1965 Zenith roundie, but he said he had to get rid of one of his other sets. He's got one set that I always liked, and I might be getting it when he gets the roundie going. It's a beautiful 1968 Zenith all tube set in a very small upright cabinet. It will be my first Zenith all tube color set. I'm definitely looking forward to adding this one to the collection.

Electronic M
01-23-2017, 07:14 PM
Tuning knob looks to be a random spare... I've got one with that face mask and tuner arrangement from ~1969. If yours is the same chassis as mine then there will be a chassis mounted chroma demod IC and ~2-5 passive transistors mounted to the chassis.

TUD1
01-23-2017, 07:22 PM
What chassis no?

TUD1
01-23-2017, 07:42 PM
I've done a little research, and I think I've narrowed it down to either a 20Y1C36 or 16Z8C50 chassis.

zeno
01-23-2017, 08:09 PM
Probably the 20Y1C36
Tuner knob should be chrome T-shaped. Common step-up
layout for 3 yrs. Only transistors on main chassis would
have been for AFT IIRC. This was our first colored set. The
old man got it to watch the '67 Red Sox in the world series.
They can run forever. Ours had the bridge rects go under
warranty then I changed a few tubes over the years to perk
things up. CRT never went bad or had a cataract. Lost track
of it in the mid 80's, he wanted a cable ready set.

73 Zeno:smoke:
LFOD !

TUD1
01-23-2017, 08:33 PM
Probably the 20Y1C36
Tuner knob should be chrome T-shaped. Common step-up
layout for 3 yrs. Only transistors on main chassis would
have been for AFT IIRC. This was our first colored set. The
old man got it to watch the '67 Red Sox in the world series.
They can run forever. Ours had the bridge rects go under
warranty then I changed a few tubes over the years to perk
things up. CRT never went bad or had a cataract. Lost track
of it in the mid 80's, he wanted a cable ready set.

73 Zeno:smoke:
LFOD !

Thanks for clearing that up, Zeno. I'll call tonight and see what it is. Update: Just talked to my friends. Confirmed that it is a 20Y1C36, and it also has the correct tuning knob now.

TUD1
01-23-2017, 11:57 PM
I'm really confusing myself right now. I don't remember if he told me it was 20Y1C36 or 20Y1C38. I found an old thread on VK with a set that's almost identical to mine, but it has the 20Y1C38 chassis.

BigDavesTV
01-25-2017, 12:44 PM
I had a concentric-tuned Zenith like that, in a slightly different cabinet, and mine was a 20Y1C38 chassis. These are really nice sets working and adjusted properly!

DaveWM
01-25-2017, 01:21 PM
Single transistor in the video amp section. Good solid TV. Prob work fine as is. def not one that will need to be recapped.

One thing to keep in mind when working on Zenith, there are a LOT of parts under the chassis that can be moved around (and shorted on the leads) if you are not careful on handling it. The service saver bottom removed with the chassis still installed is the way to go. May have some voltage regulation issues, IIRC on mine that was a problem. Think it had something to do with the varistor used in the regulation circuit, its not a shunt like RCA.

DavGoodlin
01-25-2017, 04:30 PM
I have an identical model on a swivel base, chassis 16Z8C50. I love that style! Like Dave says, these are among Zeniths that used 6HS5-6HV5-6JD5 HV pulse regulators and the varistor causes issues. Doug Harland, a hero VK member to all owners of 67-72 Zenith sets, found a good replacement. If I find that thread Ill link it.

Due to Zeniths superior engineering and circuit design, individual electrolytic caps in lower working voltage ranges can cause odd symptoms, if open. Best to check all with an ESR tester when you have it on its side and bottom cover off. My experience is that the black electrolytics (25v and 50v) with red or yellow ends are usually NOT a problem but gray axial lead caps that look Japanese sometimes go open.

TUD1
01-25-2017, 04:47 PM
I was told that the picture on this TV kind of "breathes". HV regulation problem? I have not seen this TV in person since May, and I have never seen it work.

Electronic M
01-25-2017, 05:14 PM
Could be HV regulation, pincushion, PS lytics, or even rapid swings in 120V wall voltage (I get that here occasionally).

TUD1
01-25-2017, 08:57 PM
I suppose I'll have to dig out my high voltage meter, wherever it may be.

TUD1
01-28-2017, 02:36 PM
TV is now in my possession. Checked every tube, replaced about 7 or 8 of them. Lots of grid emmission and shorts. Cleaned the tuner and did greyscale, purity, and convergence. Convergence was god awful - I don't even know how he was watching it like that. CRT is pretty dim, might Clean and Balance it with the B&K 470.

TUD1
01-28-2017, 02:37 PM
Convergence.

TUD1
01-28-2017, 05:38 PM
The CRT in this thing is trash. It tested decent, but the picture quality is very poor. Hardly any contrast and very dim. I put my brightener on it, and my dad is watching it now. It has a little more brightness with the brightener on it. I think it's an RCA Colorama tube. I know it has a green halo, but so does my other Colorama.

old_tv_nut
01-29-2017, 10:59 PM
If the CRT tested well but the picture is dim, I would hesitate putting a brightener on it until you do some further testing to see if there's something wrong with the chassis. No sense burning out a good CRT if the problem is really somewhere else.

Have you checked the DC voltages on the CRT? Do you have a scope and a schematic with waveforms to check the video output amplitude?

DavGoodlin
01-30-2017, 11:00 AM
Also make sure your video output tube stage is not the issue. I forget if that was the 12GN7.

TUD1
01-30-2017, 11:12 AM
Checked the 12HL7, it was fine. I'm going to try adjusting the AGC as soon as I find a screwdriver long enough. Ran a brightener on the CRT for about 30 minutes, and it's wide awake now. It's way brighter, but the picture is still very washed out and lacking contrast. Here is a picture of it next to my CTC-25, which has a perfect picture.

Electronic M
01-30-2017, 11:28 AM
I'd turn the color off, and adjust fine tuning and AGC for best picture...If color don't work at that fine tuning setting then that is a separate issue that should be addressed. If you can't get good monochrome picture contrast I'd recommend checking DC voltages along the video chain. On Zenith sets you can often un-solder the video det diode or unplug the tuner and directly inject composite video at the detector output...If you see a noticable improvement in contrast with vid injection then your IF or tuner most likely have issues (check tubes, and change tubular film/paper caps first)...Though AGC could also affect RF/IF gain, and should be looked at.

Normal AGC control action should have a range of no-signal at bottom, low to high contrast, overload with sync loss and or negative picture. Adjust up till you hit overload then back down just a tiny bit below/after the point where sync returns.

dieseljeep
01-30-2017, 11:56 AM
Checked the 12HL7, it was fine. I'm going to try adjusting the AGC as soon as I find a screwdriver long enough. Ran a brightener on the CRT for about 30 minutes, and it's wide awake now. It's way brighter, but the picture is still very washed out and lacking contrast. Here is a picture of it next to my CTC-25, which has a perfect picture.

Make one out of a wire coat hanger, like we used to do.
Cut the hanger apart, hammer the end flat and if no file or grinder is handy, form the end on the concrete steps or sidewalk. Bend a loop on the other end for a handle. :D

TUD1
01-30-2017, 12:38 PM
I hadn't thought of that. Thanks! I've got wire coat hangers everywhere. I checked every single tube when I got it. It still needs a 6U10.

BigDavesTV
01-30-2017, 12:47 PM
Looks quite nice, good job, U.D.1! CRT looks a little tired, but not too bad.

DavGoodlin
01-30-2017, 04:16 PM
The Zenith looks a bit brighter but I agree your issue may be in the video output stage, which affects the contrast. If you start by replacing paper coupling caps and any electrolytics through the 1st and second video stages, it can only improve. Need a schematic?

Years ago I worked on enough Zenith consoles from this era to know they can have a moderate issue and still look close to normal. Ill check my notes in the "TAB" color TV service manual for Zenith.

After all, Zenith used to advertise extra components were used that other manufacturers (think GE here) did not include. The downside of all those parts is that when one would fail, it was not any thing resembling a common symptom. Open electrolytics could present in some very strange ways.

TUD1
01-30-2017, 05:53 PM
Adjusted AGC using a homemade screwdriver that I made blacksmith style. Contrast is still pretty poor, and focus isn't so great either. Also looks kind of fuzzy and unclear next to the CTC-25.

TUD1
01-30-2017, 07:58 PM
I think I found the source of all the fuzziness. A shorted 6GJ7 in the VHF tuner. And I'm sure the shorted 6U10 horizontal oscillator can't be helping much either. This thing was FULL of dead tubes!

Replaced 6GJ7 and 6U10. No improvement, but I did find the source of the fuzziness. This TV is incredibly picky with its input source. I have it on a splitter with the CTC-25, and it does not like it one bit. If I plug in the source directly into the VHF tuner, it's fine, but with the splitter, it has lots of squiggly interference. The RCA does not. Nuvistors anyone?

TUD1
01-31-2017, 12:44 AM
The VHF tuner is really starting to act up. Here are some pictures of what it's doing now. The only way I can describe it would be like watching TV through a burlap sack.

DavGoodlin
01-31-2017, 10:52 AM
You're getting real close here but a tube is not causing what we see. That tuner may need to have its channel 3 and 4 strips cleaned off with alcohol. Clean plugs on the IF cable from the tuner also.

Then flip your $ervice $aver $et on its side, try a new 4mf-450 volt cap from pin 8 of the 12HL7 to ground. Contrast and video sharpness in general can be affected by this screen bypass cap AND tack in another 50 mf cap from the center post of the CONTRAST control to chassis. This has to do something positive here. Next try the electrolytic capacitor around the 6BA11's AGC section (pins 2 thru 8).

old_tv_nut
01-31-2017, 11:03 AM
I think I found the source of all the fuzziness. A shorted 6GJ7 in the VHF tuner. And I'm sure the shorted 6U10 horizontal oscillator can't be helping much either. This thing was FULL of dead tubes!

Replaced 6GJ7 and 6U10. No improvement, but I did find the source of the fuzziness. This TV is incredibly picky with its input source. I have it on a splitter with the CTC-25, and it does not like it one bit. If I plug in the source directly into the VHF tuner, it's fine, but with the splitter, it has lots of squiggly interference. The RCA does not. Nuvistors anyone?

If the interference occurs when you have both sets turned on, turn off the RCA to make sure it's not radiating back into the Zenith. Probably not, but doesn't hurt to check. Also check for broken RF cables.

TUD1
01-31-2017, 11:07 AM
The Zenith has interference regardless of whether the RCA is on or not. When I went through the Zenith, I cleaned the tuner with tuner cleaner and a rag, cleaned the IF wire going to the chassis, and the tube sockets.

TUD1
02-01-2017, 09:40 AM
Found the problem! The wall wart from my AM transmitter was right behind the tuner, and it was causing interference. Unlugged it, perfect picture on both sets.

dieseljeep
02-01-2017, 10:20 AM
Found the problem! The wall wart from my AM transmitter was right behind the tuner, and it was causing interference. Unlugged it, perfect picture on both sets.
The Digital Stream DTV converters have the AC cord passed through a ferrite bead or sleeve to minimize the SMD noise.

JB5pro
02-01-2017, 10:27 AM
You know the tuner knob is wrong on yours.
The one i serviced had a warped channel drum keeping tuner from turning. I got one from zenith.
So, i always wondered if it was a bad design or more likely a well intended tech put wrong bulb that was too hot?

TUD1
02-05-2017, 09:50 PM
Just checked the HV on this TV, and I could not believe it when my meter read 36 KV. Adjusted the HV as low as it would go, and got it down to 29 KV. Probably one one those durned varistors.

DavGoodlin
02-06-2017, 09:59 AM
Just checked the HV on this TV, and I could not believe it when my meter read 36 KV. Adjusted the HV as low as it would go, and got it down to 29 KV. Probably one one those durned varistors.

You're lucky you have a CRT yet.
I had a 1967 Zenith lose HV regulation. The arcing broke the CRT neck off its 25GP22.

Electronic M
02-06-2017, 10:09 AM
I'd check the tube and all components in the HV reg circuit....I thought the varistor problem normally resulted in low HV, if it is going opposite of normal then you likely have other problems to address.

TUD1
02-06-2017, 11:15 AM
Maybe I'll check the HV tubes when I get home. It wouldn't surprise me if they're bad.

zeno
02-06-2017, 11:50 AM
Maybe I'll check the HV tubes when I get home. It wouldn't surprise me if they're bad.
Also be sure it has the right damper/ regulator pair.
Check the tube chart. Some list several pairs.

73 Zeno
LFOD !

dieseljeep
02-06-2017, 12:50 PM
Also be sure it has the right damper/ regulator pair.
Check the tube chart. Some list several pairs.

73 Zeno
LFOD !

The earlier chassis used a 6CJ3 and a 6HV5, heaters connected in series.
You had to use a GE or Zenith branded 6CJ3. There was a lot of Raytheon Japanese tubes designated 6CJ3/6DW4, that had a different heater current and wouldn't work in series with the 6HV5.
IIRC, the heater in the 6HV5 was receiving reduced heater voltage and wouldn't regulate properly. :thumbsdn:

JB5pro
02-13-2017, 07:31 PM
Utube... bewitched blow you a kiss in the wind.
Very cute perfornce by sarina, that devil woman.
Great bouce & hart song apparently written for the show.