I picked up this Zenith 29JC20 last week at the Richmond Antique Radio and TV museum estate sale. My hope is to restore the set and use it daily. Here are some pictures of it before I get started. It's PVA has started turning green. I may attempt the cataract removal process if it affects the picture much. The cabinet is a little rough but not too bad. The service tag (PSI?? weight??) lists a bunch of service in the late 60's. The Picture tube is a 21FJP22A rebuild dated late 1973. Looks like its got the same tie-strap around the cloverleaf that I read about on other 29JC20s. Looks like some recent replacements of a few capacitors with orange-drops and only two small electrolytics. First I will check the picture tube with my slightly flakey CR70. Then I plan to shot-gun the old caps, the electrolytics, replace all the off value resistors, check the coils, and replace the bad tubes before I power it up. I am curious how this narrow band chroma set with RE phosphors looks compared to my 21CT55 with its 21AXP22A (my avatar/signature).

My very first concern with that set would be the integrity of the plastic/(nylon?) coil form of the H efficiency coil, which tends to crystalize over time and fall apart. If that happens, the requisite 'dip' in cathode current of the H output tube is lost, allowing the current to soar 'waay over spec.

Very nice.. These Zeniths seem to be popping up lately.. I wonder how the CRT is..

I'm going to be getting one in a few weeks, so this should be an interesting thread.

The service tag (PSI?? weight??) lists a bunch of service in the late 60's. ----

The Picture tube is a 21FJP22A rebuild dated late 1973. ----

I am curious how this narrow band chroma set with RE phosphors looks compared to my 21CT55 with its 21AXP22A (my avatar/signature).

I'm guessing that the tag *actually* belongs on a fire extinguisher. :scratch2:

Picture will be brighter for sure, but will you enjoy the colors as much as your wonderful 21CT55? Be interesting to see side-by-side photos when you are finished restoring the Zenith.

jr

Zenith sets do tend to have rather sharp monochrome detail, focus, and contrast...It can be so good that one can still think the picture looks good with moderate tint and gray scale miss-adjustment....Granted later roundys and rectangular Zeniths are what I'm familiar with. The only RCA based set that could hold a candle to it is my CTC-4, but the 4 don't get good color at the same fine tune point as monochrome, and the sound is best at a third spot so it could be an alignment fluke.

My very first concern with that set would be the integrity of the plastic/(nylon?) coil form of the H efficiency coil, which tends to crystalize over time and fall apart. If that happens, the requisite 'dip' in cathode current of the H output tube is lost, allowing the current to soar 'waay over spec.
At the moment mine is still intact. Is there some way to visibly see that it is crystalized? On other sets where the ferrite cores have been tight, I have let them soak in a little WD40 which seemed to ease their movement. Any suggestions for this coil?

I used a hair dryer to loosen them, then some gentle prodding with the twiddle stick is usually all it takes.

Very nice.. These Zeniths seem to be popping up lately.. I wonder how the CRT is..

:banana: Apparently the CRT emissions are good! :thmbsp: I coaxed my CR70 into working. My CR70 was tripping its power switch/breaker when I had this CRT plugged in and all set up. I found that turning the filament range setting all the way down, switching it on, and then bringing up the filament adjust to the 6.3V kept the switch from cutting out. Guess I should re-cap the CR70? Anyway it showed good emissions on all three guns, even with 5V on the filaments.

I'm guessing that the tag *actually* belongs on a fire extinguisher. :scratch2:

Picture will be brighter for sure, but will you enjoy the colors as much as your wonderful 21CT55? Be interesting to see side-by-side photos when you are finished restoring the Zenith.

jr

I am guessing that the more narrow chroma bandwidth will just mean a lower color resolution than the wideband 21CT55. It interesting that the current crop of 4K displays are using this same high-res luminance + lower-res color to lower the bandwidth to allow HDMI 2 to drive 4K:
http://hdguru.com/hdmi-2-0-what-you-need-to-know/

I think its based on the human eye seeing B/W in higher resolution than color.

Dave

I used a hair dryer to loosen them, then some gentle prodding with the twiddle stick is usually all it takes.

I will definitely give that a try. Gentleness counts on these old sets.

Dave

At the moment mine is still intact. Is there some way to visibly see that it is crystalized? On other sets where the ferrite cores have been tight, I have let them soak in a little WD40 which seemed to ease their movement. Any suggestions for this coil?
From the photo, it looks like the coil form is phenolic. If so, you're in luck. The whitish, semi-clear plastic forms are the ones that crystalize.
If the three blue adjustment coils on the convergance board also have phenolic forms, you're doubly in luck.

...I think its based on the human eye seeing B/W in higher resolution than color.

Dave
That's exactly right. That's why earlier hi-resolution chroma was fudged to simply 'paint' color in the BW image.

From the photo, it looks like the coil form is phenolic. If so, you're in luck. The whitish, semi-clear plastic forms are the ones that crystalize.
If the three blue adjustment coils on the convergance board also have phenolic forms, you're doubly in luck.

Yes the convergence board coils also look the same. From a couple of tags on the set I think it was made in 1963. Maybe Zenith changed to phenolic coil forms by then.

Maybe Zenith changed to phenolic coil forms by then.

It is the other way around. The phenolic forms are the old type, and Zenith moved away from them to the notorious plastic forms that they had from the mid 60's to the late 70's.

I tested the coils today and I think they are all ok. There is some wax on the bottom of the HV cage but the flyback otherwise looks and tests good. I'm not sure how concerned to be about the amount of leaked wax. The flyback shows 16 rings on my Sencore LC75. The 3A3 plastic socket cup is broken but I think it might be fixable. The cloverleaf has split and looking back at the service tag it lists a 43-473 which is the part number for the cloverleaf. So this set has had two of them and I guess both broke. I wonder if separating the cloverleaf into the three sections at the place where the plastic springy area is and then using an actual metal spring between the section could work.

I spent most of the day checking the resistor values and replacing the ones I thought were too far off. The Zenith solder cups makes it easy to lift one end to check values. I replaced all the resistors that were beyond or close to their tolerance band allowance. That ended up being 40 resistors. I like to replace resistors with higher wattage replacements, like 1W where there were 1/2 W. Next are the old non-ceramic capacitors and then the electrolytics.

I spent most of the day checking the resistor values and replacing the ones I thought were too far off. The Zenith solder cups makes it easy to lift one end to check values. I replaced all the resistors that were beyond or close to their tolerance band allowance. That ended up being 40 resistors. I like to replace resistors with higher wattage replacements, like 1W where there were 1/2 W. Next are the old non-ceramic capacitors and then the electrolytics.

Out of curiosity, how many resistors were bad and by how much (worst case)?

I also have one of these sets, so I'll be watching.

I notice two holes punched in the tuner bezel... Does this have an optional UHF Tuner? If so, I've never seen them arranged side-by-side on a Zenith roundie... Usually it's diagonal.

Out of curiosity, how many resistors were bad and by how much (worst case)?

I also have one of these sets, so I'll be watching.

I notice two holes punched in the tuner bezel... Does this have an optional UHF Tuner? If so, I've never seen them arranged side-by-side on a Zenith roundie... Usually it's diagonal.

Worst case resistors were (Sams numbers) 470K ohm R184 was 950K ohm, 470 R82 was 1084, 22 R39 was 36.1, 22M R129, R130, R131 were 30.3M, 30.2M, and 32.5M. The rest were over, at, or just under their tolerance above their design value. I wanted all of the resistors to be within their tolerance, figuring they specified that tolerance for a good reason. I did find one bad factory solder joint on R158 that made it read open when checking between leads of the parts it connected to.

Yes this set has a UHF tuner which mounts to the right of the VHF tuner (when facing the front of the set).

Dave

Today I replaced the caps that were not mica, ceramic, or electrolytic. The Sams photos show bumble-bee (black beauties?) where my set had mainly Sprague orange-drops and brown-drops plus a couple of other tubular caps. I think the cleaner looking orange-drops were recent replacements as most of the orange-drops had a dirty film on them. Most of the orange and brown drops had leakage of around 1-15 uA at their rated voltage and some measured outside their uF tolerance, .0068 C46 was .0087, .15 C6 was .206, .056 C129 was .0647, and a couple caused my Sencore LC75 to not read properly even when out of circuit. I replaced them all with in tolerance valued capacitors, not wanting to trust 50 year old caps.

I started the first of the three multi-cap electrolytic can capacitors and found that the section labeling (square, triangle...) on my capacitor can does not match the Sams, but the chassis was wired as the Sams shows. So my capacitor values do not match those shown on the schematic or the parts list. I don't think this is a Sams mistake, for the following reason. The Sams schematic shows C3C as a 4 uF 150V cap with a blank label marking. The Sams shows that section wired as the cathode bypass cap of the V7 AGC tube with 35V across it. My set does have the V7 AGC tube wired to the blank labeled section, but in my can that section is a 40uF 25V cap. Which puts a 25V capacitor where Sams shows 35V. Here is what the Sams schematic and parts lists as the sections and what my can has:
Section Sams My set
A (square) 50uF 450V 20uF 450V
B (triangle) 40 uF 25V 4 uF 150V
C (blank) 4 uF 150V 40 uF 25V
D (1/2 round) 20 uF 450V 50 uF 450V


Ok, what am I missing here? Is it just a Sams error? But if so, then why does my set have a 40 uF 25V section connected to the V7 AGC cathode which Sams shows at 35V, unless that Sams measurement is wrong....

Also, Sams shows the 50 uF on the screen of the audio output tube, but the 20 uF on the power input to the vertical output transformer. Wouldn't it make more sense if the vertical output transformer power had the 50 uF and the audio output had the 20 uF? Should I just wire it as original?

Dave


Dave

I bought a Zenith Color TV Service Manual VOLUME ONE (1973) in hopes it might cover the 29JC20 and have a schematic I can compare the Sams to.

I was able to fix one of those broken plastic cups with some flex zap (a CA glue that has modifiers in it to make it less brittle.

Its still not as strong as an unbroken one but its ok, just have to be gentle with it.

That Fly looks fine.

I was able to fix one of those broken plastic cups with some flex zap (a CA glue that has modifiers in it to make it less brittle.

Its still not as strong as an unbroken one but its ok, just have to be gentle with it.

That Fly looks fine.

That's a relief about the flyback. I already put some Loctite plastic bonding epoxy on the broken HV cup. As long as I never pull the rectifier out I think it will hold...

Now there is a part that would be a prime candidate for 3D printed reproductions. It's small and the originals were plastic anyway.

Now there is a part that would be a prime candidate for 3D printed reproductions. It's small and the originals were plastic anyway.

Yeah a 3D printer would be very handy to make one of these. I wonder if the 3D printing materials would hold up to high voltage?

Well now. I am a field tech for a company that sells and services copiers and network printers. It just so happens that we are going to start selling 3D printers and they will be sending us one for the showroom, as well as sending someone to train us to service them. Don't know when, but this might be a doable project. I will post later when we get it later this year. We have to learn to print something, might as well be a vintage tv part.

I finished replacing all of the electrolytics. I removed all of the connections from the old electrolytics and mounted the new ones on the underside of the chassis. For now I have wired the caps as per the Sams schematic. The Zenith manual I ordered should be here in a day or two and I will compare the schematics.

I also checked the diodes and found a problem with the three section convergence diode. Two of the diodes read like a silicon diode. The third is shorted. Can I just use three 1n4007s for these? I think I read to use Schottky diodes but I don't know what current or PIV should be. A suggested part number would be great if anyone has had success with it.

Dave

Yeah a 3D printer would be very handy to make one of these. I wonder if the 3D printing materials would hold up to high voltage?

If you don't let it print hollow, it should...If not you can always thicken the walls in a cad program, and try again. Those convergence coil frames that like to crack are also prime candidates.

I've noticed all three of these I've seen pop recently, the clover leaf assy are broken..

I spent an evening checking the values and wiring for the parts I replaced. I'm glad I did, as I found one wrong value resistor, 1.5K instead of 15K, and two other resistors each with one lead to the wrong solder cup. All the caps values and wiring were ok.

I got the Zenith Color TV Service Manual by R. L. Goodman but it did not have a schematic for the 29JC20. I did have the 27KC20 which has most of the same circuitry for the electrolytic can I was concerned about. The 27KC20 schematic, as well as some information from the Oct 62 Radio Electronics page 71 showing the vertical supply cap as 20 uF, confirmed the Sams values for the four sections of the capacitor. My set was wired as the Sams schematic and parts list section markings, but my cap has the sections with different markings. Here are pictures of the Sams parts list markings of the sections and a picture of my can. You can also see that the 22-3632 can part number matches the parts list Zenith part number. I think my set was wired wrong from the factory. Its now wired as the Sams schematic shows.

Next I'm gonna check the tube socket resistance measurements to see if I messed anything else up.

I finished replacing all of the electrolytics. I removed all of the connections from the old electrolytics and mounted the new ones on the underside of the chassis. For now I have wired the caps as per the Sams schematic. The Zenith manual I ordered should be here in a day or two and I will compare the schematics.

I also checked the diodes and found a problem with the three section convergence diode. Two of the diodes read like a silicon diode. The third is shorted. Can I just use three 1n4007s for these? I think I read to use Schottky diodes but I don't know what current or PIV should be. A suggested part number would be great if anyone has had success with it.

Dave
Should be a 103-### on the part. Cross it to NTE. You can get
the specs that way.

73 Zeno

Should be a 103-### on the part. Cross it to NTE. You can get
the specs that way.

73 Zeno

Its a 212-25, the other diodes are 103-###. A google search for "NTE 212-25" did return a "212-25 NTE Equivalent NTE116 1A 600V rectifier,
NTE116 General Purpose Silicon Rectifier 1A 600prv"
I will try 1N4007s. Thanks.

Dave

One of the three convergence selenium diodes I thought was bad was just an incorrect in-circuit reading due to a coil. Once I isolated that diode it read ok. So for now I'm gonna leave it as is and come back to it later if I have convergence issues.

All the resistance readings checked ok, although I had to reverse polarity on the ohm meter once. I started cleaning the sticky goo off the wires to the CRT, yoke, tuner, and controls. Iso alcohol works well to take it off. After that, next is mounting the patched up HV rectifier socket and replace the bad tubes. Then I can try powering it up.

The HV socket really had a tight grip on the 3A3, so I bent the socket pins open a bit to loosen their grip in hopes pulling the tube will not break the socket plastic mounts. I had to grind some of the epoxy off of the outside patched up shattered HV socket mounts to get the socket to fit over them. I used new 6-32 machine screws short enough not to bottom out in the plastic. Here is a picture of the socket re-installed. I added some washer because the plastic around the mounting holes was cracking. The 3A3 and the 6BK4 are the original Zenith tubes with dates codes of 62-04. Even though they both tested ok I put in new tubes. I used a 6BK4C/6EL4A in place of the 6BK4.

I powered the set up on the bench without the HO tube and got good supply voltages and some noisy TV audio. I added a jumper to make it easy to check the cathode current on the HO and VO tubes. When I put the chassis back in the cabinet the chassis control shafts did not line up. The chassis control shafts were testing on the opening in the cabinet front and made turning them tough. I enlarged some holes so I could tilt the controls up enough to line up right.

I put the chassis back in the cabinet, reconnected everything and powered it up. Here are some pictures.

Yes we have a raster :thmbsp:. Good HV, good raster, good CRT, but I could not get much audio or video. Turning the fine tuning did very little. Seems like a tuner problem.

I unplugged the tuner output and drove the IF with the Sencore VA62 45.75 modulated video and tone. I performed the Sams setup procedure and found the HO cathode current was 210 mA. Sams shows the current should be 190 mA. The horizontal efficiency coil was already adjusted at the dip. I could reduce the current by increasing the HV adjust, but it was 28KV to get it under 200 mA. My line voltage was at 118V, but I have measured it at 125V in the past.

I powered the set through my variac and tried different line voltages and read the HO current. Here is what I got.

At 125V the HO current was 225 mA. At 115V it was 200 mA. At 110V it was 190 mA. The picture didn't change much. I decided to add some dropping resistors in series with the line input. I used four 8 ohm 20W resistors in parallel and mounted them to a terminal strip and the line fuse on the top of the chassis in an open spot. That dropped my 118V down to 111V which gave me 190 mA HO cathode current. The raster fills the screen and I have 25.5kV high voltage. I'll settle for that.

Dave

I would not be surprised if the original 6BK4 was good. I've seen them work when they had much more x-ray blackening. X-ray blackening is usually a function of run time so I'd guess you have a low hours set. :thmbsp:

When I first tested the set, the fine tuning did not have much effect. I removed the tuner side cover and saw that a plastic gear engages a fine tuning screw on each channel coil insert. The plastic gear had split down its length. A goggle search for 14 tooth 1/4" diameter with a 1/8" inside diameter 3/8" long gear shaft turned up everything but what I needed. I could epoxy it, but that would probably fill up the gear teeth which might cause more splits. If I could find the right inside diameter c-clip/cir-clip I might be able to put it around one end of the gear and fit it into the tuner, but there is not much room in there. I noticed that only about half the length of the gear had dark grease marks on it from engaging the tuner screws. So I'm going to experiment with using some heat shrink tubing to squeeze the gear at the end that does not seem to engage the tuner screws. Here are some pictures of the split gear, the gear with two layers of heat shrink on one end, and with it mounted back on its shaft. The shaft has teeth that engage the inside of the plastic gear. The shaft is driven by the fine tuning knob and the mechanism moves the gear to engage it into the tuner screw teeth. The gear now fits snuggly on its shaft and works surprisingly well, for now...

Dave

I made an attempt modify the broken cloverleaf to get the convergence coils closer to the right positions. I cut the cloverleaf coil support section apart and put springs between them. The put it back together, but its really too floppy and needs more work. I wanted to make an initial attempt at getting some kind of picture. I quickly set purity and convergence. The tuner now sort of works. Here are pictures of the cloverleaf and the first pictures using channel 3 RF. When the set is first turned on I get some color but it quickly fades away after a few minutes. There is also quite a bit of ringing in the video when there a large image contrast changes. I will take a look at it on my scope. Probably will need to do an IF alignment, or maybe its just a wiring mistake I made.

Dave

I've fixed mucho many of those FT gears that 'd split. Just clean the shaft and gear thoroughly of all grease. Then apply epoxy sparingly to only the splined area of the shaft using something like a toothpick, and slide the gear back on. Never had one fail.

Re. the cloverleaf, back in the day there was an aftermarket item for that, consisting of a bungee sized to fit snugly around the outside perimeter. What you're doing is just as good, probably better.

I've fixed mucho many of those FT gears that 'd split. Just clean the shaft and gear thoroughly of all grease. Then apply epoxy sparingly to only the splined area of the shaft using something like a toothpick, and slide the gear back on. Never had one fail.

Re. the cloverleaf, back in the day there was an aftermarket item for that, consisting of a bungee sized to fit snugly around the outside perimeter. What you're doing is just as good, probably better.

Thanks for the tuner gear tip!

Dave

Looks like a decent pic already, I think you'll find the ghosting is an IF/tuner issue. Probably alignment time.

I wonder if a Velcro strap wrapped around that cloverleaf would hold it in place?

Looks like a decent pic already, I think you'll find the ghosting is an IF/tuner issue. Probably alignment time.

Yep, looks like most of it is in the IF stages. Here is a picture of driving the tuner input to the first IF with 45.75 MHz modulated with video. And another driving composite video into both the sync video takeoff and into just after the video detector. There does seem to be a little undershoot in the video stages, or maybe just from the unterminated VA62 video signal cable I used. My cheap camera white balance changed colors between the two pictures, it looked the same to my eye.
Dave

I wonder if a Velcro strap wrapped around that cloverleaf would hold it in place?

That would help firm up the angles between the pole pieces. I also see that the green is titled back some. Maybe I need a ring of plastic to hold then in the same plane.

Dave

Before even thinking of messing with alignment, try subbing the last IF tube. It can cause ringing that can be mistaken for misalignment.

On that stripped gear, your shrink tubing collar is a good idea in addition to epoxy. "Belt and suspenders" redundancy.:nerd:

Before even thinking of messing with alignment, try subbing the last IF tube. It can cause ringing that can be mistaken for misalignment.

On that stripped gear, your shrink tubing collar is a good idea in addition to epoxy. "Belt and suspenders" redundancy.:nerd:

I tried changing each and all of the three IF tubes with some change to the ringing. Three new tubes in place of the originals does have a bit less ringing. I will try an alignment this weekend.

I'm gonna add the epoxy to the gear too.

Dave

maybe some delay line ringing?

I tried changing each and all of the three IF tubes with some change to the ringing. Three new tubes in place of the originals does have a bit less ringing. I will try an alignment this weekend.

I'm gonna add the epoxy to the gear too.

Dave

I found that all of the Zenith color roundie convergence coils are interchangeable. The latter ones might not aesthetically correct but at least they are better made and more rugged.

The epoxy trick would not fix the broken fine tuning gear on my Zenith. The reason was that the plastic appeared to have shrunk and epoxying it would have left a considerable gap between teeth at the break. What I did was to cut an O from the end of a BIC pen, the inner diameter of which was roughly equal or slightly smaller than the gear when compressed to close the gap. With the fine tuning shaft removed, I heated it with a large soldering iron until it would just begin to melt the gear and then with gear compressed around the shaft, I slipped on the BIC ring to hold the gear compressed.

Fix ensured the gear melted into the splines and there would be no gap between the teeth where the break was. It was bit fiddley to fabricate and install, but the result worked like a charm.

maybe some delay line ringing?

I just tried adjusting the delay line termination potentiometer. It did not affect this ringing.

Post #44 shows pictures of test pattern video driven into the first IF showing ringing and then composite video driven into just after the video detector that does not show nearly as much ringing. Sure seems like it's in the IF stages.

Dave

oh my yes, I missed that. I wonder if all the little ferrite beads are in place etc. on the filament leads? My later zenith (24MC32) has several IIRC on the IF filaments. Mine also has a 22k resistor across the secondary of the IF before the 3rd IF tube. Wonder if maybe that has drifted high? I assume its there to damp out oscillation.

oh my yes, I missed that. I wonder if all the little ferrite beads are in place etc. on the filament leads? My later zenith (24MC32) has several IIRC on the IF filaments. Mine also has a 22k resistor across the secondary of the IF before the 3rd IF tube. Wonder if maybe that has drifted high? I assume its there to damp out oscillation.

My first two IF stages filaments have a ferrite bead, as well as a couple more beads in the filaments some color circuit tubes. I did check and replace out of tolerance resistors in the IF stages, being careful to match lead dress as close to original as possible.

Before I started to do an IF alignment, I took some pictures of some video test pattern waveforms taken at the input to the first video amp. All the tuner and IF tubes have been tested and swapped with not much difference in the ringing. I used my Sencore VA62 to generate a channel 3 RF signal displaying the single vertical and horizontal line cross. The first video amp input scope picture shows the ringing. I then set the VA62 to generate its 10 section multi-burst which is a set of white and black vertical lines of increasing frequency from 0 to 4.5 MHz. The second picture shows the poor frequency response.

Here is a picture of the SAMs IF frequency response. Figure 1 is the third IF and figure 2 is the first and second response. The next picture shows the third IF response is pretty close to what SAMs shows (you have flip the plot horizontally to match my scope). The next picture is what I got for the first and second IF response. Its way off. The response at the 45.75 MHz marker shown should be much lower amplitude. Following SAMs alignment I tried to adjust A6, the 41.25 MHz trap and found it very hard to turn because its core was coming apart. I pulled the chassis, removed the coil, and removed the core. One end had two small pieces broken off. I tried a shorter ferrite core to see if the coil form was too tight. It was very tight. I ended up finding that a 1/4"-28 tap matches this ferrite core. So I tapped the coil form as shown in the next picture. The last picture shows the shavings removed from the coil form. The small ferrite core now threads nicely though the core. I am trying to glue the two small ferrite pieces back onto the broken core. If they hold, I will invert the core so that the broken pieces will be at the end that is not usually used for adjusting. Anyone know of a place to buy 1/4" threaded ferrite cores?

Dave

Here is a picture of the SAMs IF frequency response. Figure 1 is the third IF and figure 2 is the first and second response. The next picture shows the third IF response is pretty close to what SAMs shows (you have flip the plot horizontally to match my scope). The next picture is what I got for the first and second IF response. Its way off. The response at the 45.75 MHz marker shown should be much lower amplitude. Following SAMs alignment I tried to adjust A6, the 41.25 MHz trap and found it very hard to turn because its core was coming apart. I pulled the chassis, removed the coil, and removed the core. One end had two small pieces broken off. I tried a shorter ferrite core to see if the coil form was too tight. It was very tight. I ended up finding that a 1/4"-28 tap matches this ferrite core. So I tapped the coil form as shown in the next picture. The last picture shows the shavings removed from the coil form. The small ferrite core now threads nicely though the core. I am trying to glue the two small ferrite pieces back onto the broken core. If they hold, I will invert the core so that the broken pieces will be at the end that is not usually used for adjusting. Anyone know of a place to buy 1/4" threaded ferrite cores?

Dave

I've got a bunch (~ half of a cigar box full) of ferrite cores - how long?

I always pulled the cores from sets I junked - and at my dad's shop, I was the TV stripper/parts puller/gofer. I probably have junked over 300 sets in 30+ years. First we saved everything, then just certain chassis, then just modules, and finally, only good chassis/CRTs. My user name comes from my attitude - if you find it, keep it. Someone, somewhere will likely need it.

Cheers,

I've got a bunch (~ half of a cigar box full) of ferrite cores - how long?

I always pulled the cores from sets I junked - and at my dad's shop, I was the TV stripper/parts puller/gofer. I probably have junked over 300 sets in 30+ years. First we saved everything, then just certain chassis, then just modules, and finally, only good chassis/CRTs. My user name comes from my attitude - if you find it, keep it. Someone, somewhere will likely need it.

Cheers,

Nice. All I could find online were ferrite interference filter beads. I need two 1/4" by 5/8" long cores. If you have them, let me know the cost and shipping charges. Thanks.

Dave

I powered the set through my variac and tried different line voltages and read the HO current. Here is what I got.

At 125V the HO current was 225 mA. At 115V it was 200 mA. At 110V it was 190 mA. The picture didn't change much. I decided to add some dropping resistors in series with the line input. I used four 8 ohm 20W resistors in parallel and mounted them to a terminal strip and the line fuse on the top of the chassis in an open spot. That dropped my 118V down to 111V which gave me 190 mA HO cathode current. The raster fills the screen and I have 25.5kV high voltage. I'll settle for that.

Dave

I am just curious as to how this aspect panned out for you. I am working on a similar vintage Zenith and your findings are almost identical to what I was finding in my set except I can't get 190mA. More like 200 or maybe 210 at 110V. My flyback seems hotter than I would like it to be after about 30 minutes of operation. I am waiting on a replacement socket for my HV rectifier which was burned up and the 1W resistor was open (blasted in two).

I had long been searching for the source of a very light HV hissing that was intermittent. It couldn't be seen down inside the insulating cup of course. I think that we should be able to achieve correct cathode current at full line potential. Like you, I used a variable source to control this, but I don't think it would be necessary to use that or alter the line voltage in a healthy set. Also, I found that just having the raster fill the screen is not guite all my set needs. The higher line voltages (above 110V) around 115V or up give a much crisper or clearly defined picture once video comes into play.

Nice. All I could find online were ferrite interference filter beads. I need two 1/4" by 5/8" long cores. If you have them, let me know the cost and shipping charges. Thanks.

Dave

PM sent.

I am just curious as to how this aspect panned out for you. I am working on a similar vintage Zenith and your findings are almost identical to what I was finding in my set except I can't get 190mA. More like 200 or maybe 210 at 110V. My flyback seems hotter than I would like it to be after about 30 minutes of operation. I am waiting on a replacement socket for my HV rectifier which was burned up and the 1W resistor was open (blasted in two).

I had long been searching for the source of a very light HV hissing that was intermittent. It couldn't be seen down inside the insulating cup of course. I think that we should be able to achieve correct cathode current at full line potential. Like you, I used a variable source to control this, but I don't think it would be necessary to use that or alter the line voltage in a healthy set. Also, I found that just having the raster fill the screen is not guite all my set needs. The higher line voltages (above 110V) around 115V or up give a much crisper or clearly defined picture once video comes into play.

I have been attempting to align my IF so my set has been on for up to a couple hours at a time. I still have my Simpson 260 in series with the HO cathode and have been keeping an eye on it. So far it is holding at about 190-195 mA. I turned it off after it had been on for over an hour and felt the flyback. It was certainly warm but not burn you fingers hot. I will use an IR thermometer on it next time I have it on for a while and report the result. If it would help, I can also take some voltage readings. You may want to replace all of the capacitors in the HO section and verify that all of the resistors are within their tolerance. A leaky HO grid cap could elevate your current.

Dave

PM sent.

Thanks very much for your kind help!

Dave

I put my glued together ferrite core back in its coil and put the set back together. Then I tried using the Sams IF alignment procedure. It did help some. The Sams procedure tells you to use a demodulator probe at points after the detector. This did not work for me. I used a normal scope probe and got reasonable waveforms. The Sams also shows three IF sweep curves but the alignment text only refers to two of them. After the Sams alignment procedure I did get rid of the ringing in the video but also lost color. I could not match the curves response in the 42-43 MHz range. I used the VA62 multi-burst and tweaked the IF adjustments to get more color signal frequencies through (3 to 4 MHz) and got the color back. But when looking at a channel 3 RF signal I got a noisy picture.

I looked through the R.L. Goodman Zenith Color TV service manual and found a more detailed IF alignment than the Sams. It showed similar sweep curves but its procedure referred to all of them. So my next attempt will be to use this alignment procedure. The procedure is general to cover several Zenith sets, including the 27KC20 (which has very similar design and is the successor to my 29JC20), so some test point designations require translation to use on my set. I am no whiz at aligning sets, but I am determined.

Dave

I am just curious as to how this aspect panned out for you. I am working on a similar vintage Zenith and your findings are almost identical to what I was finding in my set except I can't get 190mA. More like 200 or maybe 210 at 110V. My flyback seems hotter than I would like it to be after about 30 minutes of operation. I am waiting on a replacement socket for my HV rectifier which was burned up and the 1W resistor was open (blasted in two).

I had long been searching for the source of a very light HV hissing that was intermittent. It couldn't be seen down inside the insulating cup of course. I think that we should be able to achieve correct cathode current at full line potential. Like you, I used a variable source to control this, but I don't think it would be necessary to use that or alter the line voltage in a healthy set. Also, I found that just having the raster fill the screen is not guite all my set needs. The higher line voltages (above 110V) around 115V or up give a much crisper or clearly defined picture once video comes into play.

You may also want to check the cathode current of the 6BK4. The Sams for my set says to adjust the HV to 24kV and make sure it is at least .9 mA. If I recall right, mine was about 1.9 mA with 24 kV. The schematic showed a 25-26 kV voltage and the 21FJP22A spec has a maximum rating of 27.5 kV. I adjusted my HV for 25.5 kV. I noticed that my HO cathode current went down with the higher HV setting. Maybe you can reduce your HO current by raising the HV, if your CRT and set will permit it.

Dave

I used the R.L. Goodman Zenith Color TV Service Manual IF alignment procedure. It took three iterations but the result matched the sweep diagram pretty well. Here are pictures of the Goodman response curve, the result I got, and the Multiburst response. The alignment got rid of some of the ringing seen on the CRT, but what was left was a dimmer wide repeating pattern. Here is a picture of the video waveform before and after the delay line. I found that the delay line termination potentiometer was open. I opened it and cleaned off the oxidation. I then worked fine, so I put it back in.

Here is a picture of the single vertical and horizontal convergence pattern that had so much ringing when I first powered up the set. The color would initially work and then fade away when I first powered on the set after the recap. I found that the second chroma output was fading. It is gain controlled using a bias from the color killer modulated by Zeniths Automatic Color Control. For now I cheated and just put a resistor in parallel with part of the bias filtering to increase the gain to keep the color working. It still kills the color on black and white video and seems to work fine otherwise. Here are some pictures of video through the tuner. I may make one more pass through the IF alignment and then do the audio alignment. The audio has a little distortion in it at the moment.

That looks really good !

I'm wondering about the blue dipping on both ends at the edge of the screen.....
Could the zip tie around the convergence magnet assembly be changing it's
orientation from a perfect perpendicular to cause the dipping....?

Imagine if the magnet was forced towards the back of the yoke, and not
straight up and down, then if it is trying to make the line straight, but
orientation is wrong, pushing the line lower on the ends.... If the magnet's
orientation was forced away from the yoke would the line go up at the ends
if it's all working correct....?

Or am I all wet, and it's most likely a aging part, or the best it's gunna get....


.

...
I'm wondering about the blue dipping on both ends at the edge of the screen.....
Could the zip tie around the convergence magnet assembly be changing it's
orientation from a perfect perpendicular to cause the dipping....?
.
The three coils on the convergence board are blue line adjustments. One of them (I forget which one) is for the horiz blue line.
A word of caution: one of those , if you back the slug out too far, will roast one of the pots. So go easy.

Hi !

Not what I was getting at..... On the first page of this thread a picture is posted of the
3 convergence coils held on the neck of the picture tube with the help of a zip tie.
I was just wondering if this method changes the orientation of the coil, with respect
to the electron gun, and it is either tilted towards the yoke a little, or away from it
and results in the downturning of the blue line in the cross pattern on the screen
in a posted picture on this page of this thread....
Left most picture post #64.

.

Hi !

Not what I was getting at..... On the first page of this thread a picture is posted of the
3 convergence coils held on the neck of the picture tube with the help of a zip tie.
I was just wondering if this method changes the orientation of the coil, with respect
to the electron gun, and it is either tilted towards the yoke a little, or away from it
and results in the downturning of the blue line in the cross pattern on the screen
in a posted picture on this page of this thread....
Left most picture post #64.

.
Take a look at post #39. I have removed the tie-strap and am experimenting with some springs to try to space the pole pieces closer to correct. The green plastic is cracked and is allowing that pole piece to tilt some. More work will be required to position them properly. I would try to find a Zenith replacement part but this set has already had this plastic piece replaced before and it has failed twice. Also, I have only done a very quick convergence on the set, as I have been moving the chassis between the work bench and the cabinet as I test and fix problems. So yeah, its nowhere near done yet. I just wanted to show the results of the alignment, the delay line terminator repair, and the color kludge. At least it now has a good start on a watchable picture.

Dave

The three coils on the convergence board are blue line adjustments. One of them (I forget which one) is for the horiz blue line.
A word of caution: one of those , if you back the slug out too far, will roast one of the pots. So go easy.

Thanks for the warning. I started my first convergence by trying to center the convergence adjustments. I need to replace a ferrite core in one of those coils, so the convergence you see now is just enough effort for testing and fixing the rest of the set.

Dave

Sorry there Z I guess I missed a few pages in the middle of your story.....
In #39 you have the assembly removed. A possible fix could be laying it down like
you did, put it in as close a position as possible, and tracing out the outside
perimeter of it, and making a plastic holder for it - a big circle - with cutouts
for the "cloverleaf" and silicon glue the plastic circle to the CL - maybe put shims
along the way to get position just right..... Might be more rigid than springs....
and not interfere magnetically..... 1/4" or thicker sheet plastic..... Maybe
even polypropylene, or polyethylene.... A little softer, and immune to a lot of
stuff..... Give it less brittle start....

.

Sorry there Z I guess I missed a few pages in the middle of your story.....
In #39 you have the assembly removed. A possible fix could be laying it down like
you did, put it in as close a position as possible, and tracing out the outside
perimeter of it, and making a plastic holder for it - a big circle - with cutouts
for the "cloverleaf" and silicon glue the plastic circle to the CL - maybe put shims
along the way to get position just right..... Might be more rigid than springs....
and not interfere magnetically..... 1/4" or thicker sheet plastic..... Maybe
even polypropylene, or polyethylene.... A little softer, and immune to a lot of
stuff..... Give it less brittle start....

.

I certainly need something to keep them in place better than just the springs.

I got better results with another alignment. Here is a picture of the sweep with the marker at 42.75 Mhz and 45.0 Mhz. And a picture of the multiburst showing 0-4.5 Mhz making it through the tuner to the first video amp. This alignment also reduced the ringing of the single vertical line, as shown in the magnified scope image in the fourth picture. The last is what this alignment looks like on the CRT. I think this alignment is a keeper.

Dave

I went through the audio alignment which fixed the distortion in the sound and increased the volume a lot.

Neither of the yoke centering adjusting strings would move. I took the yoke off the CRT and was then able to move the strings a little. Working them back and forth a bit seemed to free them up. I put the yoke back on and fired up the set to try to use the centering strings. The strings moved the centering rings but for some reason the image on the CRT does not move. I wonder what I am doing wrong. The image does fill the CRT and the centering is not off by a lot. It still would be nice to get it centered though.

Dave

Your 29JC is looking good. I have the manual scanned for it I could send you a link to if you don't have it. Just PM Me.

Your 29JC is looking good. I have the manual scanned for it I could send you a link to if you don't have it. Just PM Me.

I'd be interested in a copy too.

The Zenith are prone to line pairing, I've found you can improve the interlace by fine tuning the Vert hold. They say increasing the integrator resistance also helps.

The Zenith are prone to line pairing, I've found you can improve the interlace by fine tuning the Vert hold. They say increasing the integrator resistance also helps.

Could you point out which resistor(s) using the attached Sams diagram? I have not replaced the K1 and K2 networks. I do see that the odd and even horizontal scan lines seem to be offset horizontally from each other when I look at the color bar pattern. If you zoom in on the color bar patter in post #35 you can just see the offset. Thanks.

Dave

I found a note in Goodman about the cause of the centering strings to not adjust the centering. The glue fails and the magnetic rings no longer move. I am going to try to re-glue mine.

Your 29JC is looking good. I have the manual scanned for it I could send you a link to if you don't have it. Just PM Me.

Wow, cool! PM sent.

Dave

I took my centering rings out and re-glued them. Here are some pictures. There is a plastic ring at the end of the centering strings. The plastic rings are glued to the magnetic rings. The glue on mine had failed. I used some epoxy to glue them back on. There is a spacer between the magnetic rings and thick paper ring with tabs that holds them in place. The centering strings now work fine.

I went through the chroma alignment. Only one adjustment needed tweaking. The set came without chassis hold-down bolts so I bought some that seem to do the job ok. I bolted the chassis and tuner in. About half of the plastic knobs snapped in half when I originally tried to pull them off. I used some epoxy for plastics and with some fiddling got them back on. I had to substitute an old knob for the color level control as it was missing. The UHF numbered dial indicator knob is missing. I only plan on using channels 3 or 4 but I'll keep an eye out for one if I can find a picture of what it looks like. I went through purity and convergence again. I still need to come up with a way to hold convergence pole pieces in alignment over the guns. Next I'm going to make mounting plate for a fan to get cool air into the HV cage. I plan to remove the rivet the access cover pivots on, remove it, and screw the fan plate in its place.

The first two pictures are of the fan I added to exhaust hot air from the top of the HV cage. The 12VDC fan is powered from the 6.3V filaments through a voltage doubler rectifier. I put the fan where it would exhaust the hot air generated by the HV regulator tube. There is a slot in the plastic plate that the fan mounts to. The slot is where the air enters. I epoxied a smaller piece of plastic to direct the cool intake air to the flyback first. So the flyback gets the cool intake air, then it goes by the HV rectifier, then the regulator heats it, the hot air rises and the exhaust fan pulls it out the top. I watched a 2 hour movie on the set last night and then felt the flyback right afterwards. The flyback was barely warm. :yes:

The last two pictures are of a ring of plastic with Velcro to hold the convergence pole pieces in alignment over the guns and to keep them from flopping over. The springs keep the pole pieces against the CRT neck but also made them want to flop over. Not the greatest solution, but it works ok.

Dave

This is a 3/4" wide Velcro wrap that I use for holding battery packs in my planes. I forget exactly what it's called, but it comes several feet on a roll. Seems to be self stabilizing, and you can tension it up a little.

http://i452.photobucket.com/albums/qq245/Kuehn/Velcro%20Convergence%20Magnet%20Strap/VelcroConvergenceMagnetStrap001_zps7e07f33e.jpg?t= 1424559278

http://i452.photobucket.com/albums/qq245/Kuehn/Velcro%20Convergence%20Magnet%20Strap/VelcroConvergenceMagnetStrap004_zpsef352939.jpg?t= 1424559276

Hey- that velcro wrap looks wide enough to be pretty stable.... Good thinking ! !
Simple fix too ! Always best.

.

Well it seems simple, but I'm not sure how critical the magnet spacing around the neck circumference will be? My cloverleaf is only broken in the one location, so it's throwing the magnet spacing off a little. I guess I'll find out when it's time to do a convergence. In the mean time it's doing a decent job of holding everything in place.

Well it seems simple, but I'm not sure how critical the magnet spacing around the neck circumference will be? My cloverleaf is only broken in the one location, so it's throwing the magnet spacing off a little. I guess I'll find out when it's time to do a convergence. In the mean time it's doing a decent job of holding everything in place.

That does look like a better option than my fix. I was concerned about the spacing but now I'm not sure it makes that much difference as long as the two pole pieces of each convergence coil is over their respective gun pole pieces just inside the CRT.

Dave

I was concerned about the spacing but now I'm not sure it makes that much difference as long as the two pole pieces of each convergence coil is over their respective gun pole pieces just inside the CRT.

Dave

Dave, that's good to know. One could take this one step further and put a piece of adhesive Velcro on top of each magnet assembly(similar to what you have) and then wrapping the strap around the outside. That should help stabilize the spacing.

Here are some pictures of the results of the restoration. The convergence is certainly a compromise. The multiburst shows video response through 3 MHz with 3.58 filtered out and maybe just a little at 4 MHz. I added a 22 uH choke in the screen circuit of the video output pentode patterned after a later Zenith set with a peaking adjustment.

Dave

Looks very nice from here. :thmbsp: Is the Ovation software by chance a free download?

Actually its an old DVD titled "Avia Guide to Home Theater" 1998-1999 by Ovation Software Inc.

Here are three pictures of the Zenith 29JC20 playing the Wizard of Oz. For comparison, here are two pictures (not quite of the same DVD frames) taken on my 21CT55 from a couple years ago with my same cheap camera. The Zenith has the 21FJP22A while the RCA has the 21AXP22A. I guess I would have to do a better job of getting the black and white tracking and the color tracking make a real comparison.

Many thanks for all the restoration suggestions and especially to Findm-Keepm for the ferrite cores. Two are now in the Zenith replacing broken IF and convergence cores.

Dave

beautiful pictures. a great job you done on the zenith.

that set looks great!takes me back to the old days and watching the new
zenith color sets at lazarus in columbus.

I have been sensitive to narrow band R-Y, B-y chroma verses wide band I,Q chroma since I got my 21CT55 up and running. This was my observation of picture quality based on a side by side comparison with a CTC 4.


When I bought my 21CT55 for $50 in '64, I brought it into the house after I got it working and ran it along side my Dad's old CTC4 he left me. Both had 21FBP22s so it was a good comparison of narrow bw color R-Y B-Y vs. full bw color I Q. The extension of full color into fine detail on the CTC2B was startling! Color persisted in fireworks until extinction which I never saw before. The CTC4 fireworks turned into white long before extinction. The CTC2B carried full color way into the shadows, the CTC4 went gray to black. I kept the CTC4 in the house for the kids but brought the CTC2B back to the garage workshop for further study. Ease of working on the chassis and CRT "forced" me to destroy the cabinet and configure the remains into the vertical chassis configuration I am blessed with today. That’s alright with me. I respect the original CT restores but that’s not my thing.

Thanks for the kind words guys. Your assistance to overcome difficulties with these old sets really helps.

Dave

I can only hope that my efforts give the results that your skills brought with your Zenith!

Looks great, good job!

Your set looks great and the picture looks great to. Good Job!!

This is a 3/4" wide Velcro wrap that I use for holding battery packs in my planes. I forget exactly what it's called, but it comes several feet on a roll. Seems to be self stabilizing, and you can tension it up a little.

http://i452.photobucket.com/albums/qq245/Kuehn/Velcro%20Convergence%20Magnet%20Strap/VelcroConvergenceMagnetStrap001_zps7e07f33e.jpg?t= 1424559278

http://i452.photobucket.com/albums/qq245/Kuehn/Velcro%20Convergence%20Magnet%20Strap/VelcroConvergenceMagnetStrap004_zpsef352939.jpg?t= 1424559276

That Velcro strap is called One-Wrap. It has hooks on one side and loop on the other. It work great for reusable cable straps instead of zip ties. I've used it for all sorts of things and once it's stuck to itself it's fairly strong.

That came out sweet. I always thought roundies had
the best pix especially with the older movies & anything period
from NBC. Bonanza will look even better than the Wiz.


73 Zeno:smoke:

The more I watch this set, the more I like it. The picture does not have the detail I see in my 21CT55, but it does have the full range of colors and a nice range of saturations. Its a pleasure to watch.

Dave

Looks great ! ! Good Job !

.

I'm impressed with the picture quality no matter what - Wizard of Oz, shows well! A pleasure to view, thanks.

If it is not too much trouble I'd be interested to see pictures of the tuners from inside the cabinet particularly the UHF tuner.

If it is not too much trouble I'd be interested to see pictures of the tuners from inside the cabinet particularly the UHF tuner.

Here are the two pictures I took of them when I first started on the set. The first picture shows the VHF tuner from its right side (picture tube side when mounted in the set). The second picture shows the UHF tuner whose shaft is at the same level as the VHF tuner when mounted in the set. When I got the set the tuners were not mounted and it was missing its UHF tuning dial. I only use the VHF, which works quite well, so I'm happy. I can take more pictures of it mounted in the set if that's what you are looking for.

Dave

Nice tuner pkg. Even in the day we saw few U tuners
with a tube.
If you havnt swap out the 1st video amp tube even if it
tests good. It can make a huge difference in detail. They
tend to roll off at the higher freqs especially on Admirals.
They go from seeing no hair on a head to lots of hairs !

73 Zeno:smoke:

Thanks.
I have a UHF scale knob (not the knob you'd grab) from a later chassis. I don't know if it would fit your set, but I might be willing to let it go.

Cool, PM sent.