1967 Zenith 24NC31Z roundie color tv
 

Hi Everyone,

I'm new here to Videokarma. I have a 1967(1966) Zenith roundie tv. It has raster, but no actual picture or sound. It seems as if it is not getting any signal from the tuner. Where should I start looking to resolve this problem? Any assistance would be appreciated.


Thanks,
Frank :scratch2:

Could be nearly anything, how are your electronics skills?

Pics please!

if its got no snow at all and no noise at all just a snow free blank raster, then I would check the osc tube in the tuner. But as mentioned it could be a lot of things, but for starters the tuner and the IF tubes would be a good place to start. Some times just wiggling tubes will bring it back to life as oxidation on the tube pins can interupt the circuits.

it really should be checked over for things like HOT current as leaky caps can cause damage to parts that are hard to replace. that being said, zeniths do hold up well and typically require minimum cap replacement.

pls post a pic, always nice to see the set in question.

Wiggle the normal/service switch possibly?

good point esp if the serv switch has a 3 position (normal,grey scale,purity_

Forgive me for raising the most obvious - If it is hooked to an antenna, not cable, VCR, or satellite dish, you will need an analog-to-digital converter box (do you find that some channels have brighter, thicker "snow"and lounder noise on some channels than others?

Next suspects would be the tubes in the tuner and in the IF strip (the little thin tunes in a line on the part of the chassis closest to the tuner).

A whole bunch of other things figure, countless caps, insufficient B+ due to a power supply problem (which could blow your whole project up!), even a video amp tube (can also knock out the sound).

I'm in the same boat as you (just acquired a Zenith roundie myself).

I, too am curious. What is the signal applied to the antenna terminals?

Zeniths do seem to need IF tubes quite often, probably because they've lasted so long as to wear them out. Could also be as simple as a dirty tuner. I've seen some that were totally blanked out by that.

I've checked the tubes in the tuner, and they check OK. I have found some other bad tubes, and am waiting for them to come in. I will be posting pictures of the set soon. This is the set I have, The Barstow, as pictured in the sales brochure.

which tubes tested bad?

As far as the signal, it is hooked up to digital cable, via a converter box, and also to a dvd player, via an rf convertor. I have a 1964 Magnavox stereo theatre(b&w) also hooked upto the same signal sources, and it plays great, so it's not an issue with the signal.

I've also replaced the IF tubes (all three).

your video dvd should have a composite video out. I would try and connect that up at the output of the video detector diode (thru a .05 cap to be safe). This will clear the problem up thru the output of the video detector.

Hi Dave,
Would that be the green lead comming out of the tuner? My knowledge is sort of basic.:headscrat

test point D on the set, its on a term strip, if you are lucky you will see a paper tag on it, or it may be stamped into the top of the chassis IIRC. its not a wire on the tuner, its after all the IF stages, then there is a diode (which could also cause the issue but I doubt it).

I assume not only are the tubes good in the tuner but they are lighting up and getting B+ as well?

the cap will block any DC from the set, there should not be any, but it just in case you inadvertantly touch a B+ it will save your DVD. Aways a good idea to check the TP with a multimeter to check for DC before connecting anything up.

opps hold up, wrong zenith, I will have to check to see if that D is still the right test point

well not sure I did not have that schematic I have a 25NC38 and a 24MC32. You need to get a schematic for that, one of the video detector output test points will be indicated. that is the composite signal. done expect it to be a great pic, the PP is prob not going to be the same, but you will at least see something.

the other way to check would be just to scope it if you have a scope.

I finally got a chance to check over the set. What I hadn't noticed before is that the first 6EH7 tube in the IF wasn't lighting. I rechecked the tube and it tested ok. I straightened the pins on the tube so that it would fit the socket better, and it lit. Sound and picture are now back, even better now with the new tubes.

tube wigglling is always the FIRST thing to do on a very old tube set. Glad you got it going. some contact cleaner and a brass bristle brush on the tube pins is aways a good starting point on a restoration of an old tube TV set.

I have also restored old radios and TVs to operating condition by simply wiggling tubes in their sockets, cleaning said sockets with contact cleaner, and straightening pins. Sometimes the most obvious and simple things (such as your set's 6EH7 failing to light) can stop a TV right in its tracks. When I lived in a Cleveland suburb some years ago, I would pick up old radios and televisions on trash day; many of these sets had literally nothing wrong with them except one or more loose or dead tubes. I once had a Zenith table radio which I picked up at a thrift store; the set wouldn't work, but within five minutes I found out why. A fusible resistor under the chassis was open. I replaced it; the radio immediately began singing again.

Hold on to that Zenith 24NC31Z TV if you can, as they don't make them like that anymore. Those older Zenith color sets were built to last and to work well, which is more than I can say for a lot of the offshore flat-panel sets these days (although my Insignia 19" FP, bought new in August this year, has a better picture, IMHO, than either of my CRT sets, both 19" as well). When you bought a Zenith you could expect it to last 15-20 years easily; today's FPs (yes, even the ones with the Zenith lightning bolt on the display panel frame) are made, or so it seems, to last two years or until the end of the warranty period, whichever comes first. The original Zenith Radio Corporation's emphasis was on quality, not just in the television chassis itself but also the cabinetry -- those old sets had solid wood cabinets, although compared to other sets Zenith cabinets were rather plain-looking.

The pictures on these older sets, however, were excellent by late-1960s NTSC standards; typical Zenith. Hook up an ATSC->NTSC converter box and an antenna to your set and get ready to enjoy TV as never before -- the converter box will allow you access to more channels (carried on subchannels of your area's network affiliates) and will even convert your set to remote control, except for power switching. The TV on-off button on a DTV converter box remote will not work if the television is not already set up for remote power switching, although all other basic functions offered by the box (volume +/-, channel +/-, mute, et al.) will work perfectly.

I mentioned in another post to a different thread that the remote on-off switches on a very long cord can be used for TV power switching, although I don't think these switches are available anymore except, perhaps, in thrift stores or at flea markets. The trend these days is to wireless remote control, so your best bet is probably to find a wireless remote unit as used for lights. However, be sure the controller (the unit that plugs into the AC outlet and that your TV plugs into) can handle the power draw of your set. Many if not most of these wireless remote systems are intended for use with lights only; they cannot handle a 300-watt-plus load -- the relay in the controller will be damaged or destroyed instantly if it is used with an old TV, or anything for that matter, that draws more than 100 watts.

It is interesting to learn that the throw-it-away mentality is not just from the 1990s or the 21st century. In Chicago in the 1970s, we would often find furniture or other items but I did not yet know electronics enough to drag home any TVs hoping I could fix one.

I often see these cords for sale at Christmas time, intended to let you turn your tree lights off and on without crawling under or behind the tree.

After seeing one of those "Christmas" remotes at a friends house (he was using it to control a table lamp) I had to find one. Originally I wired it into a ceiling fixture which didn't have its wall switch in a very good location. That little remote is very handy. Wait 'til the end of the year, you can probably pick one up cheap. I wonder what other functions you could rig them up to do?

I just thought of a good use for one, if they can handle the power: Plug a power strip into it, and then plug all of your regular TV devices into it (TV, cable/satellite box, Blu-ray player, stereo system). Then, when those devices are not being used, you have a "hard" power switch to eliminate all of the standby power used by them. The same concept can be used for computer equipment (CPU, monitor, speakers, maybe printer except some printers use extra ink each time they are hard-powered on).

I think if you have several televisions plugged into a power strip and flip the switch, smoke and sparks will come out of that little switch. My guess is that they are good up to no more than 100 watts. A decent color set (vacuum tube type) will draw about 300-325 watts. Now have several on at the same time and stand back!

Some of the wired Power "remotes" can handle a TON of juice. I've had one set up to handle the front half of the masssive Christmas light display (I had to seperate it into halfs as the load was too much for the GFI outlet), and it could handle all the the current that the GFI could stand quite well.

I know first hand how much juice Color sets can draw....I have a wall of color sets (shown below) and between the four sets, my stereo, the lighting, and what ever was on in the other rooms on that line I was able to trip the breaker.
http://i1095.photobucket.com/albums/...y/DSCN0429.jpg

The roundie has the nicest picture. :p

The bottom or the top one?

The color bars on the bottom one look much better. :rolleyes:

:lmao: Seriously?

If you read my post you probably know why that sets "picture" looks different.
I coulden't run them all at once (without going to the effort of stealing power from the air conditioner outlet) and the bottom one despite haveing what I think is the best grayscale among them has lousy colorimetry, and the color bars tend to bleed into eachothers edges, not to mention other small issues that I will someday take on.

The upper roundy has(especially back when I took that picture) great colorimetry, but has some small issues that detract from that. I usually run the top two, and (when the rectangualr one is not having focus issues) watch that one for fine detail/ledigible text, and watch the roundy for that glorious lolipop color.

Would anyone have any spare control knobs ( the ones behind the flip down door under the CRT) for the set in the thread title? I'm missing ALL of them.

Thanks,
Frank

I have the control box complete with knobs for a Zenith roundy, but I don't know the model. It can be seen in the right midle of the photo. If the knobs look right to you let me know.
http://i1095.photobucket.com/albums/...y/DSCN1136.jpg

Hi Tom,
The two red knobs might work, but the tan ones seem like they may be too short.

Thanks,
Frank

I'll try to dig them out and get better pictures for you this weekend.

Thanks Tom.

Hi All,

I finally have pictures of this beast working. The cabinet is not the best, and it does not have it's original legs, but it does give a great picture.

looks nice!

Hi all,
This set has now developed a new problem; the contrast seems to flicker from dark to light, and every once in a while, the picture will break up. I know it's not the signal source. Also, when it is first turned on, it also seems to take a while to lock on to horizontal. Any ideas where to look first?

Thanks,
Frank

could be AGC acting up. does the contrast adj work ok? try wiggling the AGC tubes, move the agc adj pot back and forth a bit.

If it was just a horz issue I would guess the AFC diodes, but if is seems like the pic fade is with the sync lock, the AGC is suspect.

If you have a variable dc source you could try clamping the AGC and see if that settles it down, check the 4uf cap in the AGC circuit.

Does anyone have the bulb number for the channel light? The number lights up in the panel above the knob. I know Doug had it in an earlier post.

If the set used what I call a light-through channel selector knob (the kind with little filmstrips around the inside of the knob bearing the channel numbers and UHF, through which the pilot light shone and projected the number onto a small screen in the center of the knob) Zenith sets used in the '60s, I'd guess the correct replacement would be #47, as used in flashlights, but that's only a guess; later sets such as yours, with a channel indicator that lit up translucent numbers on a disk in a panel above the selector knob, may well use a different type of bulb, even in a different base. Use of the incorrect type of bulb may result in premature failures, if the bulb happens to be rated, say, for four volts and the pilot-light supply winding on the power transformer supplies six volts or more. Doug would almost certainly know more about that than I since he has had more experience with Zenith televisions than I ever did, and probably ever will.

The Zenith sets used the bayonet base bulbs. They are the same type you find in the dial lights of most 1940s table radios