Zenith 14DC16 Colour question/problem
 

Hi All, new forum member here.

I have a Zenith 14DC16 portable hybrid TV set with single button space commander remote control. Have had it since 1994, when I picked it up for free. I have used it fairly sparingly over that time, and the only repair it has required, has been a replacement of both tubes in the VHF tuner.

I have the sams package for the set, and basic knowledge about how TVs work. Audio/radio have been hobbies of mine for years, but I have only done minor repair work on TVs.

In general the set is in excellent working order - the picture is sharp and free of noise, and the picture geometry is more than decent for such an old TV. The picture is bright, and when the image is a solid colour, it is consistent over the entire screen area.

Question is as follows... when watching certain shows, especially The Simpsons, it's extremely hard to get the tint to stay the same over the course of a show. In one scene, they look yellow, then the next a bit green, and in another a bit orange. In all cases I can adjust it to the right colour using the tint control, but then later on it will be different. Not all programs seem to show this effect, but when it is happening it is really annoying, and detracts from the otherwise perfect operation of the set.

I am targeting the 3EJ7 burst amplifier, and the 9MN8 G-Y, R-Y, B-Y amplifier as possible culprits. If either of these tubes are weak, or operating in some non-linear region, I can see how this would upset the colour. I have no tubes to use as substitutes, so thought I'd see if I could get a second opinion before I start ordring parts. There appears to be no electrolytic capacitors in the colour circuitry, and I am really at a loss as to what else it could be.

Any input from someone experienced with TVs of this era would be greatly appreciated.

Does that set have the quad detector diode tube in the color circuit? Also GH8s and KT8s cause issues like this. The bright solid colors in the simpsons really test the old color sets. Their yellowish color seems to be one of the hardest colors and results in red bleed on most of the old sets I see.

Thank you for the quick reply!

So it might be something I just need to live with.

Colour section is hybrid, as follows

3EJ7 pentode Burst amp --> transistor amplifier ---> IC Demodulator ---> 9MN8 tripple triode voltage amp --> RGB grids of picture tube.

And add a number of probably germanium diodes to above

Just guessing wildly, but:

Could it be the burst gating pulse is too wide and the color sync is picking up the left edge of the video? If you record and play back some Simpsons, you could try seeing if the variation occurs according to the color at the left edge of the picture.
If this set has a horizontal hold control, try turning it slightly to see if there is a hue variation.

If you want to try a 3EJ7 I can send you one.

Chroma alignment is something I want to work on. I have a great magazine article going through the alignment of a brand new Zenith and how much better it can be made.

I have 2 identical rca ctc35 chassis and one displays the simpsons perfect and the other has the red bleed. Thats using the same crt, yoke, convergence etc...so I know its the chassis. I tried switching the tubes between the two chassis and that didnt fix it. Its an alignment or cap issue somewhere.

old_tv_nut:

Thank you for the suggestion!
I am using the TV with a digital cable box - it's strange, the horizontal hold control has almost no effect on anything. When I first got the TV, and was receiving over the air signals, the horizontal hold control was fairly touchy. So far The Simpsons hasn't been on, so I haven't had an opportunity to see what it does with colour. Next time it comes on, I am going to give that idea a try.

ctc17:

Your website is very interesting! I clicked on the link hoping to see what a ctc35 looks like and ended up spending 45 minutes looking at photos of tvs and other stuff. Drove through Death Valley for the first time myself this summer. Anyhow, would appreciate the 3EJ7. Last night I dug through hundreds of tubes, without any success finding one! I think it's at least worth a shot. Another thing about this TV, is my TV-7 tube tester is incapable of testing *any* of the tubes in the set! That's usually my first step in repairing anything with tubes in it.

Does your tube tester show a 6ej7? Use the settings for that and reduce the filament voltage to 3.

If you want to test later TV tubes, get either a Sencore "mighty mite" or one of the many B&K tube testers in the 600 or 700 series. These will test the later TV tubes, as well as older octal, loktal, and miniature radio and amplifier tubes. Also, these testers have a "grid emission" test; which, is very important for testing TV tubes. These testers were made right up to the end of tube TV production and between one of these and your TV-7, you should be able to test most any tube used in consumer electronics.

ctc17:

Why didn't I think of that! Yes, the tester does list 6EJ7. Minimum good reading is 39 -- my tube reads 10!

radiotvnut:

Passed up on one of those B&K testers about 15 years ago and regretted it... this Zenith is my only tube TV, so haven't really had a reason to seek one out, but will keep my eyes open.

Ill try and dig one out in the morning. Dont get to excited, good chance it wont make any difference.

ctc17:
It's worth a shot... Not expecting miracles. I thought the TV was worn out before I replaced the 2HA5 in the tuner. Now am adressing the less significant issues.

well bad news...I just pulled out the 4 I have and all of them test bad. 20-40%, I know its not the tester because I tried a new 6EJ and it checks 75%.

Grab one off ebay, they are only a few dollars, you can get 5 new ones for $10 so its not a rare tube at all.

hey thanks for trying!
I think i will pick up a full set of tubes for the set on ebay, minus the horizontal output tube. It looks like most of them are pretty cheap and easy to find.

For what it's worth, I'm practically up to my ears in NOS TV tubes, if you (or anyone) is ever looking for something. Just send a PM with what you need and I'll see what I can put together.

Thank you for the offer! I wish I had read that yesterday, I just placed an order for a full set of tubes for my TV, minus the horizontal output ($$$)

I have another question about this TV. What is the "peak pix" control supposed to be adjusting? On my TV, when you turn it down, the TV gets blurry, and the picture is best at the opposite extreme.

Its just that video peaking. Its like sharping pictures on the computer. I always leave them all the way up.

Does it use a xLF6 for the output tube?

it has the option of 20LF6 OR 26LX6

Currently the set has a 26LX6, with red printing on it, marked Zenith Service, with a 1978 date code. It appears as though the horizontal output, damper, and vertical output were changed when the set was around 5 years old. The set has no symptoms of a bad horizontal output, so I will hold off until either it needs it or I hav e reason to believe it will improve performance

Update on this set:

Have been brushing myself up on TV theory, and discovered some peculiarities about this TV. For one thing, it has RGB screen controls, but not drive controls. It seems to me that this is a design compromise, which makes it difficult to compensate for uneven aging of the CRT cathodes. Specifically, when the screen controls are set for proper white balance, the tint control has to be adjusted fairly far off centre towards red, in order to get accurate skin tones. Is this really a compromised design, or is there another way to go about setup?

Remembered I had another tube tester packed away. It is an EICO model 667, and once I found a comprehensive setting chart online, I was able to test all of the tubes in the TV.

Weak tubes include the final video amplifier, and also the 10Z10, as well as the colour burst oscillator. The only tube which tests in the "red" zone of the tube tester is the aforementioned colour burst oscillator. Luckily the horizontal output tests well into the green zone, at 120%

Out of curiosity I tested the old tuner tubes, 2HA5 and 4GJ7, and both tested in the "yellow" zone of the tube tester. In the set however, they completely ruin performance, the picture becomes overwhelmed with noise and snow. It makes me wonder what effect new tubes will have in other positions which are currently reading weak good, or marginal.

The set is displaying a few symptoms which seem to indicate a weak CRT, according to what I have read. Will reserve judgment until all small tubes are good, but symptoms are as follows:

1. Green appears a bit weaker than other colours, grass is always a bit browner than on other TVs. Nothing awful, but all the same apparent

2. When contrast control is anything above mid level, text on the screen has a bit of a shadow, “blooming” type appearance. It is still legible, but there is a definite loss of sharpness. This effect is worst with text on a dark background, such as movie credits or TV guide, and does not seem to affect normal video.

I havent figured that brown grass thing out yet. It seems to be one of the more common chroma issues. When you use a true ntsc color generator the yellow and green are all screwed up. I have 3 identical zenith consoles and one of them does it along with several others so I know its not the chassis design.
Its on the list of issues to figure out but it could be several months. My first step was going to be to sweep the bandpass and see what it looks like. The tint being off center could be a weak osc tube, cap or alignment issue. Most of the sets we deal with seem to have the tint all the way to one end. If your having the same green issue I am you will never get it right.

The Z10s always seem weak. The only difference you will notice is louder sound and maybe less buzz if you replace that one.

Of the three chromacolor consoles, have you ruled out that it could be a problem with the CRT?

I am inclined to think in my case it is not, in my case, because the RGB screen controls are in the middle of their rotation in order to get good white balance. Nothing is pegged. I do not have a CRT tester though, so can't be sure.

Once my set of new tubes arrive, I am going to put some more effort into this. I think in the mean time I need to do more reading about how NTSC colour works.

Yes, its defiantly the chassis. I exchanged the chassis of two of them and the brown grass issue followed the chassis.

Tubes for the set showed up last week. New colour burst oscillator seems to have cured problem. Simpsons look great now, tint control is a bit more into the red than I would like to see, but colour is stable and minimal red bleed. CTC17 has a great video about how to dial this out, and at this time I don't have the equipment or experience to do a colour bandpass alignment, but I feel as though I understand the issue a lot better than when I started into this!

Right now am in the process of acquiring an RCA 8PT, and will cut my teeth aligning that before I try it with a colour set. Luckily the Zenith has solid state IF amplifiers, so I didn't throw those out of whack by changing the tubes!

Set has a new problem. Everything is fine with brightness at normal, but when you crank it all the way up, the picture gets larger, and less bright. Why would brightness affect vertical size? Don't remember it doing this before I changed the tubes.

In general though it's back in top shape, have been watching it every day again.

The problem you are describing is called blooming and is usually caused by a weak high voltage rectifier tube. That tube is often located inside the metal high voltage cage with the flyback transformer. I have seen these tubes get so weak that when the brightness is turned up the picture disappears completely and the screen goes dark. Zeniths are great sets built for long reliable service. Keep at it and when you get the bugs worked out it will be a superb performing set.

Thanks for the explanation! I actually just changed the zenith HV rectifier to a NOS GE, which may be what brought on the problem. I bought a set of tubes for the set, and changed all of them... thought it couldn't hurt after nearly 40 years, even though about half of them tested well into the green on my EICO 667. I'll put the old one back in tomorrow. I hope to keep the TV going until the picture tube becomes too weak to
be useful... at that point I'll have to search for a replacement tube, or a lower hour TV to get one from, which looks like quite a challenge in this day and age. I always assumed I could just have it rebuilt, when needed, so never paid much attention to securing a replacement.

To expand a bit on the blooming problem (no pun intended:D), as the HV drops, it is "attracting" and accelerating the electron beam less and less, allowing the deflection angle to increase to the yoke's full deflection ability. Raster size is actually a balance between the HV and the yoke's deflection power. Since color CRTs draw much higher beam current than B&Ws, they require a much "stiffer", regulated HV supply. Bill(oc)

I put the Zenith tube back... and problem solved. I wonder why the new tube was weak? This Zenith does not have a regulated HV supply, maybe it can get away with it on account of its small size?

Simpsons are on now... I can't believe how good the colour is with new tubes... set has a new lease on life.

This TV is going to drive me crazy, but not before I get it sorted out. I've noticed a new problem with it. On some stations, when there's a lot of white in the picture, it tends to flicker... it's especially noticible with white text, and at the top and bottom edges of the picture when there's a 16x9 program playing. I don't remember it always doing this.

Put the original 6MV8 Zenith sync separator back, and worked the AGC control back and forth a bunch of times to clean the tracks a bit. TV seems back to normal, or at least a lot better. Have learned a lesson here about not changing tubes all at once!

I have a 1972 Zenith 19CC19 (there's a picture in my VK photo album). I'm assuming that your set is a 1973 model judging by the chassis number.

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Was waiting for a tow truck to show up at my house, with family member's car on the hook. Ford's 4.6L plastic intake manifold had decided to crack, and leak coolant everywhere. Shop wanted $1600 to fix, so I said bring it here and I'll do it, etc. Boring sitting around the house, so we decided to watch some TV.

"what's wrong with your TV's colour?"
"nothing, it's working fine, isn't it?"
"the colour is all wrong... look that is supposed to be purple, and it's blue"
"is it? looks fine to me.. uh oh"

Looks like I did the best I could, and got used to it.

OK found a station showing colour bars. Sat my Trinitron beside the Zenith, and no possible position of the RGB and tint controls makes them look the same on both sets. The (1979) Trinitron looks like a photo of a set of colour bars, but the Zenith will get either yellow or purple right, but not both at the same time! When purple looks good, yellow looks green, and when yellow looks good, purple looks red. Back to the bench it goes!

1) is the monochrome tracking OK when you turn color all the way down?
2) could you post a pic of the Z and S side by side with color bars?

1. I think it's good, but will check again tonight.

2. Will take some photos when home from work tonight. Should have done that yesterday!

Finally found the charger for my digital camera.
Seems like today I was able to get the two to match a lot closer, but look how far off centre the Zenith's tint control has to be!

Apologies for my extreme lack of skill in taking photos of TV sets displaying a picture.

Looks good! Do the color afc alignment procedure in the sams and it will get all the controls centered out. No special gear is needed except that color bar generator. Its usually on the same page as grey scale setup

A coupla comments:
1) The zenith looks like it has a little red purity problem (turning greenish) right down the center - I would try degaussing first. If that doesn't help, is the yoke glued on, or movable? Looks like it needs a nudge forward or back.
2) the Zenith has the typical color-correcting demod angles - makes the green bar a bit dim, the yellow a bit orange, and the magenta a bit redder - all designed so that a standard NTSC source will make the best flesh tones with the phosphors in that tube.

CTC17

I'm still trying to get my hands on a test pattern/color bar generator - if I can't get one locally I'll go the eBay or classified ad route. That said, the TV sure looks way better now than it has in ages! I want to pick up a decent VTVM too. The Sams procedure looks quite straight forward.

old_tv_nut

1) The Yoke can be moved, and Sams has instructions for how to do this too.. I think it may be an artifact of the way I took the picture though, as in person red looks fairly even. I'm also afraid of messing up the convergence and not being able to get it back :)

2) Interesting... I've always liked the softer toned picture of this TV's chromacolor tube, but the dim green sometimes makes nature scenes look a bit less vibrant than they do on the Sony.

You don't need all that. Use the ntsc generator you show in the picture and just do the part where you adjust for the slowest moving bars and the adjutment to center out the tint control. Don't bother with all the voltage adjustments. Chances are if you get some old color bar generator it will have a drifted burst crystal and youwill align the set to that. Use your camera

The sams procedure says to hook up a color bar generator, and adjust a specific coil to maximize the amplitude of the 6th color bar, and then has a waveform where all the different color bars are labeled. The other adjustments are voltage based, and there's only three coils to adjust with all else being fixed. I am assuming the test is based on the old type of color bar pattern where the bars have space between them, and don't really know how to apply this with the signal I'm getting from my cable box. Actually tomorrow I will scan the instruction page from sams and post it here, so you can see what I mean. Perhaps buying or burning a test pattern DVD would be a better option?

Looking at the picture carefully again tonight, I think old_tv_nut has a point about purity.

If you try and do all that you are going to regret it. Scan the schematic and instructions and I will help you thRough it.