Seeking advice on a found Chromacolor I

[drh4683]

This is a great TV. It's a 14DC15 chassis, introduced in 1973 and last offered in 1975. The '75 models I've seen were all produced sometime in 1974 however, I've yet to find a 14DC15 built in '75. That being said, this would be the last of the "mostly tube" hybrid chassis, while the legendary 4 tube hybrid would remain as Zenith's very last tube chassis in production until mid 1975. The model# of your set is either D3721 (1973), E3721 (1974) or F3721 (1975), all being identical in every way except for the model number prefix which designated the model year. The marketing name for this set was called the "Hals" and it was Zenith's lower end "economy" model TV. A step up would be a 14DC16 chassis which would have had AFC or in some cases, Space Command 100 remote control. I have this exact same set in my collection that I've had for years. I used to find so many of these back in the early to mid 90's and they are almost impossible to find now. You are fortunate to have found this for it's a great example of a quality tube type zenith TV in a small package.

It looks like it has much potential here. Looks like you need to adjust the color killer control so the colored snow *just* disappears. The color killer is on the back of the chassis. It's also a hot chassis. A cost cutting move which also resulted in the added benefit of weight reduction by removing the power transformer. As a result, the chassis can either be hot or neutral depending on which way you plug the set into the mains voltage. If you work on the set with the back removed and plugged in, be sure that the chassis is on the neutral leg of the 120v mains, otherwise you could be in for a surprise if you touch something and you are grounded.

You can buy an HLLY 50 mw TV transmitter on ebay, just input a composite video source from the output of a DVD to DTV converter and transmit on essentially any TV channel between 2-83. A great accessory so you can enjoy the old TV's without the mess of wires and cables hooked up to the set.

[Diode]

All,
After a long delay, I finally got around to ordering an RF modulator and a 75-to-300 ohm balun. I fired it up with a video source, and the sound and picture are pretty good! I haven't messed with too many of the settings yet, but for the moment it seems to have a bit of a greenish tint, even after I adjusted the front tint adjustment. Also, for some reason, the picture does not seem to be as sharp as other televisions I compared it with (including other CRTs-- see below).

I can probably fiddle with the rear color balance adjusts to get rid of the green, but the sharpness adjustment did not seem to affect the fuzziness in the picture. Would the "focus" adjustment help with this? If I understand Maxhifi's comment, changing out the tubes in the tuner may be required, or was the "fuzziness" he was referring to was more with regards to static and snow? I have played around quite a bit with the adjustments for oscilloscope CRTs, so I get the general theory here, but a television picture is quite a bit more complex than an O-scope trace, so I'm not entirely sure.





I apologize for the abysmal lighting in this room as well as my poor photography. For anyone curious, the television in back is an 18" Hitachi, circa 1980's-- not even old by your standards, but even so, I am happy to report that after about 30 years it remains in near-daily use. More to the point, you can see that the picture on both of these sets is quite a bit sharper than the Zenith (compare the news logos in the bottom right corners).

Also, to follow up on drh4683's comment, I found some faded numbers labeling it as "F3721L", so I would assume that it is a '75 model.

Thanks for all the info you guys have given me on this. It is amazing how knowledgeable you folks are about this! On an unrelated note, do any of you know where/if I might be able to find schematics for this? I have a basic knowledge about the general principles behind CRT's, NTSC scanning and all that, but it would be interesting to learn more precisely what makes something like this tick, preferably without having to tear apart and reverse-engineer a perfectly working set like this one. With tube circuits especially, it is fascinating to see how much designers are able to do with such a small number of active components.

[DaveWM]

if you turn the color control fully CCW so you have a B&W pic, is the green still there? if you get a good B&W and the issue is not enough tint range (but it is working just not enough range) then you likely need a a slight tweak of the burst detector transformer. I just went thru this on a CTC-12 (had some issues with color in general, replaced the burst amp tube and suddenly the tint was too green. I could have tried another tube but instead I opted t tweak the that transformer.

So you could try some tube swaps 1st (burst amp, or other tube that is in the color circuit that controls the 3.58 mhz osc) or tweak the correct coil. The tweaking should not be done unless you know which coil to tweak which would require a schematic to make sence of it. Never just start tweaking with out knowledge of the circuit and are sure what should be done.

[Electronic M]

If the black and white image is tinted it means that you need to balance the drive and G2 adjustments for proper monochrome.

Google Sam's schematic. Their sits will allow you to search your sets model and or chassis number. Don't buy the print from sam's if a local library has them it will be much cheaper to photocopy. I also have some Zenith factory manuals coming in the mail so I may be able to give you a copy if your chassis is in the manuals I'm getting.

[DavGoodlin]

What a great find you have. I thought these were gone after 1973! I have a 1972 13" Zenith with a very similar Chassis #14CC15 and it looks about the same using a DTV converter box. I'm interested in what you find gets the color improved.

[Diode]

All,
Turning down the color does not leave any noticeable tint. the problem does seem to be that the tint does not have enough range (it is turned all the way CCW, and it is still a bit green). So what exactly is this burst detector transformer? what would it look like? If it is something that can be easily adjusted, I would hazard an attempt at it, although I agree that I wouldn't feel comfortable doing anything more involved without a schematic.

I looked at that Sam's website you mentioned, although I don't know how I feel about paying $22 for a manual for a TV that I got for free... I also don't have much in the way of spare tubes on hand (a single 12AU7), so that is also not an option for the immediate future. If drh4683 is correct in stating that it is a 14DC15 chassis, would anyone here have schematics which could be scanned? Where is the chassis model marked?

[DaveWM]

looks like you need to adjust the burst amplifier output coil. Looking to see if I can find something for you. if can post a pick of the chassis from the back would help to point it out.

looks like the coil to the right of the 3EJ7 tube. starting from the back it should be the second row of tubes (thinner tubes), the second tube from the left (looking from the rear of the set. To the right of that 3EJ7 should be a coil (from the top of the chassis it is just a hole with pins around it, from the bottom you should see the coil).

That is the burst amp output coil. You need the correct tool (don't improvise here) commonly referred to as a "diddle stick" or TV alignment tool, its a hex shaped plastic tool. You may still find them at rat shack, if not easy to find on ebay.

The idea is to put s piece of masking tape on it to make a flag, so you can see how much you turn. then adj one way and see if the tint shift is correct if not simply reverse. You should not need more than a 1/4 turn so if nothing happens put it back to the starting position. Either that is not the correct coil or something else is wrong. Just don't turn in more than 1/4 and keep track of where you started.

[DaveWM]

if you want to wait I will make a video showing what I am talking about, prob sometime tomorrow.

[DaveWM]

https://www.youtube.com/watch?v=OPO9...ature=youtu.be

uploading now, should be ready in about 30 min.

[Electronic M]

If you do adjust it whatever you do don't use a metal hex tool. If you do you'll crack the adjustable core(don't ask me how I know).

[Diode]

Originally Posted by DaveWM

https://www.youtube.com/watch?v=OPO9...ature=youtu.be

uploading now, should be ready in about 30 min.

Thanks, This is exactly what I was looking for. I should have no trouble finding it now. Fair point about the plastic hex tool, though. I was tempted to try it with a metal Allen key, but I'll definitely order the proper one before I do this.

I'm going to be gone for a few days for the holidays, so you may not hear back from me on this until after New Year's.

Wish me luck, and I wish you all happy holidays.
-Diode

[DaveWM]

good luck happy holidays

oh you may find that just putting in a new 3EJ7 could fix it too, tubes are not like solid state, they can very quite a bit and in some circuits this can have fairly drastic effects. I dealt with this just recently when working on the CTC-12 that had the tint issue. In my case the tint or hue was not being consistent on a fixed image (part would be red part would be purple, and it was not a purity issue).

I had a tube that had some shorts in it that when replaced not only cured the changing hue but also shifted the entire hue toward the green. I could have tried a few other new tubes to see if I could correct the tint shift but chose to just adj a coil and fix it that way.

[old_coot88]

Is a 3EJ7 used as burst amp?
Normally it's an IF tube. I was just curious as to how an IF tube would affect tint range.

[maxhifi]

In this chassis zenith a new burst amp tube solved a quite similar problem as well as tweaking the coil with color bars displayed. Be very very careful adjusting coils in the colour section though, you can easily throw it so far out of alignment you'll never get it back without proper test equipment.

The colour IC sitting on a tube socket is sure a weird sight in this hybrid chassis, I never really understood why Zenith stayed away from circuit boards for so long and advertised it as a feature

[Electronic M]

Older PCBs can be a nightmare to service. I have a '64 Silvertone color roundy That has needed PCB solder joint touch-ups on multiple occasions, and that I define to be relatively tolerable...Imagine what techs who had to deal with it daily started to think about PCBs.