Well, here we go with another set...... :)

When I got this Zenith, it was partially recapped, and working. After making it home to Buffalo from MD, I got about 45 seconds viewing time out of it, the vertical started to shrink, and I smelled (something). Shut it down immediately, and months later, here we are at today.

Did a full recap on the set and half a dozen new tubes, and powered it up for the first time just half an hour or so ago. Zero vertical sweep (just three bright lines of color very close together, you can see the horizontal shifting around with some kind of picture), but sound and reception was right on the money.

What was odd, is that there was a prominent ticking sound coming from somewhere in the chassis, about two ticks per second, steady beat. No arcing that I could see either topside or underneath (the set has an open bottom, there was a screen of some kind there which is long departed.

I'm inclined to think vertical output transformer at this stage, but wanted to see what others thought.

check the service switch

It's in the correct position, that was my first thought. I'd be further inclined to test the switch, were it not for the very noticeable "ticking" noise.

I've heard that ticking, but on later solid state sets. Not sure what to make of it. I'd shoot some cleaner in the service switch and work it a few times real fast, just to make sure that isn't the culprit. I recall others on here having trouble with vert transformers in Zeniths.

No telling what it might be, considering that hack that worked on it before you got it :)

Wasn't sure if you were the one working on the set, Bryan, or if it was someone before you. Curious though, what was the set doing which led you to replace specific capacitors, when you got it? How long did you have it running afterwards, and did you notice anything that it did?

Tried spraying the service switch, and powered the set back up. When I switched it over to the service side, the ticking (which I'll call arcing, because I realized that's what it sounded like) went away.

Switched the set back to the "service" position to get underneath to listen and isolate it further, and by the time I laid on the floor, I heard what sounded like the same static that you hear when the picture tube lights up on some sets, and I lost raster. Shut set off immediately. Smelled something burned :sigh:

Dammit.

I'll bet it's the yoke.
I'll just bet it's the yoke.
Vert. shorted to horizintal. Probably took a resistor with it.
Bill Cahill
I've seen that happen, even on some cheap BW tv's.

I'll bet it's the yoke.
I'll just bet it's the yoke.
Vert. shorted to horizintal. Probably took a resistor with it.
Bill Cahill
I've seen that happen, even on some cheap BW tv's.

I second the yoke.
The ticking is the vert stage running, easy to hear on newer sets.
Ofter if you pull the yoke you will see a rusty spot where it
burned. Use your free test inst., your nose. The nose knows.

73 Zeno:smoke:

I had a 12" b&w portable TV, bought new in 1975, that worked well for three years, then one day I turned it on and saw a curl of smoke coming up through the ventilation slots in the cabinet. (No raster, of course. :no:) I had no clue at the time as to what was burning, but seeing your post reminded me that it could have been the yoke, one winding shorting to the other, and possibly a resistor (as Bill Cahill suggested). Typical for a small, cheaply made, tube-powered offshore-brand portable.

Talk about BPC! To the best of my knowledge and belief, no one used that term in the 1970s, but it certainly would have applied to a lot of the small, cheap no-name offshore-made tube-type portables available at the time. The sets may have worked halfway decently when they were new, but they would develop problems after a very short time, after which many of them were junked. Today's no-name flat screens are like that too. :no:

I guess this just goes to show that there were cheap TVs on the market as recently as the 1970s, and quite possibly even earlier than that. I don't know exactly when these junky sets first appeared on the market, but my best guess is the late 1960s. I had a Sharp 12" portable in 1970 that worked well all of three years (!), then developed a tuner problem which I was able to work around, at first, by propping up the VHF tuner shaft with a screwdriver; however, the set developed more serious problems a year or so later, after which I junked it. Too bad, because that set had a great picture, even on a monopole VHF antenna in the near-fringe TV area in which I lived at the time. Further, since it was made by Sharp (this was years and decades before offshore companies started slapping well-known TV manufacturers' names on BPC sets), I expected it would last longer than it did.

The yoke is a good guess. If the rate of the buzz/ tick is adjustable with the vertical hold control the vert trans and ckt is likely good at least on the primary side. Back in the day zenith roundie yokes did not fare well in south florida (at least) usualy a horizontal winding issue. Good luck!

And if you had a test jig, you could quickly eliminate the yoke as a problem.

Changing a yoke is easy enough, I don't mind. I'm not looking forward to doing a degauss, purity, and convergence setup on the set, but it beats the heck out of where it is now....

zenith purity and convergence should be easy.they tend to set up almost perfect.watch out for the coils though.when they become unwound,it could be a nightmare.good luck and post pics

Oh, I've had that happen before. Nightmare is being kind :eek:

The yoke is a good guess. If the rate of the buzz/ tick is adjustable with the vertical hold control the vert trans and ckt is likely good at least on the primary side. Back in the day zenith roundie yokes did not fare well in south florida (at least) usualy a horizontal winding issue. Good luck!
I wonder if that is the yoke with the nylon fish line strings for the horizontal and vertical centering.
I used an RCA yoke for the last replacement. The centering was close enough. :thmbsp:

When Kennedy and Cohen came to town, now defunct, they used an inexpensive B/W set as a leader. It was branded "Kenco", made by Sampo. of Taiwan. They sold them for $38.00, a lot of them!
I got several of them as freebees, as the customer thought, that it was so cheap, it wasn't worth repairing. I don't remember what went wrong with them, but was a simple cheap repair. They worked well and IIRC, I sold them for $35.00. :D

They also sold a Kenco branded Sylvania-built hybrid 19" color table model for $177.00. Unheard of at the time. :thmbsp:

Tim, that TV had probably been sitting since the 70s, I got it from the estate of a deceased repairman-his nephew told me the man never owned a color tv (?) I sorta think he never did anything with it. I think the main thing wrong with it when I got it was a bad power switch. I seem to recall that I eventually replaced the filter caps because I noticed them running warm. I don't recall any vertical issues on that one.

I wonder if that is the yoke with the nylon fish line strings for the horizontal and vertical centering.
I used an RCA yoke for the last replacement. The centering was close enough. :thmbsp:

I have this Zenith TV now and I'm trying to get it to work. I got a nos yoke for it but I don't know what the nylon strings are suppose to do. I also can't find the vertical height adjustment pot on the chassis.

The nylon strings are centering controls.

I have this Zenith TV now and I'm trying to get it to work. I got a nos yoke for it but I don't know what the nylon strings are suppose to do. I also can't find the vertical height adjustment pot on the chassis.

IIRC, the vertical height is on the front auxiliary control panel. It should be identified on the label. You have to remove the knob to adjust it.

It could likely be the vertical output transformer. My set went through two of them. The convergence winding goes bad and it can take out the two resistors that provide B+ to the vertical stages. It is not a difficult part to replace but may be a little hard to find. If you already have a new yoke, I hope that fixes it. These sets really perform well when correctly set up.

I'll take another look. Thanks for the help.

It's in the correct position, that was my first thought. I'd be further inclined to test the switch, were it not for the very noticeable "ticking" noise.

I do have a changer in a mid 60's rca home entertainment center, I'll look and see what model it it.

Well, this set is now back in my possession from a trade deal :)

So here's where I'm at.....

Now that it's got a new yoke (installed by Preston), it's got a picture, but it's rolled up at the bottom. Picture shows it with the vertical size absolutely maxed, and it still won't go to the bottom of the screen.

Now, before I go any further, he gave me the old yoke back in the box, along with this paperwork which was included in it. I'm thinking that this yoke has to be modified somehow to work in this set, but I'm not wholly sure anything was, or how to do it if it does need to be done.

Take a gander, I've scanned the paperwork in. Suggestions are appreciated :)

When Kennedy and Cohen came to town, now defunct, they used an inexpensive B/W set as a leader. It was branded "Kenco", made by Sampo. of Taiwan. They sold them for $38.00, a lot of them!
I got several of them as freebees, as the customer thought, that it was so cheap, it wasn't worth repairing. I don't remember what went wrong with them, but was a simple cheap repair. They worked well and IIRC, I sold them for $35.00. :D

They also sold a Kenco branded Sylvania-built hybrid 19" color table model for $177.00. Unheard of at the time. :thmbsp:

I recall Kennedy and Cohen being in the Delaware Valley (media speak for Philly-Jersey-Delaware). I also remember the cheapest set was a 1975 Sanyo 12" BW for $59.66 when all the others were $80+

Take a gander, I've scanned the paperwork in. Suggestions are appreciated :)
Tim, from what I can see in the instructions, you need to look at the original yoke (if you have it) and/or the schematic for the Zenith set, and remove (or add?) parts to make the new yoke match what the old one has. The schematic of the new one is in the one page you posted. Other may have a better way to describe this. I have not worked on any Zenith color sets, though.

I doubt its the yoke, I would take a look at the PP drive signal, and/or voltages in the vert circuit. This is another place the TV analyst comes into play, a good source for a Known vert drive.

Yep, just got a text from Preston. He made the appropriate changes to the yoke before installing. Now, to get a Sams....

if you don't have the scope or tv analyst, the 1st place to go is a sub of the vert out tube and if used a vertical osc, IIRC Zeniths used two tubes for vert sweep (unlike the multivibrator dual triodes used in RCA).

I would test by subbing tubes.

after that you would want to check the voltage from the height pot. Assuming it uses boost voltage in the osc circuit, there is often a high meg resistor in series with a height pot. check to see if the pot and or resistor has drifted high.

The other likely suspect would be any eletrolytic that is a cathode bypass of the vert out. If that cap opens it kills the gain and output of the tube.

If you have a scope the 1st thing to look at would be the PP at the grid of the vert out, this would quickly narrow down to either the drive signal (vert osc tube) or the output (vert out tube). from there you can focus more closely on where to look.

Tim,
I checked my Zenith service manual and it confirms DaveWM on a resistor that feeds 870 volt boost to the V height pot.

Also noted that the .1 mf/600 V cap from boost to one leg of the horiz eff coil will cause the HV to be intermittent.
It notes this should be replaced with a 1000 volt cap.

BITD, I worked on maybe one or two of these sets, compared to RCA, Zenith roundies were not seen much.
Good luck

For the problem pictured, I would go for the vertical integrator. Looks like a three legged brown ceramic disc but it has three wires coming out of it.

The plate load resistor of the V.osc is a very common failure. It drifts high due to constant hammering by high level pulse.
Common problem not just in Zeniths but all designs using B Boost to feed V.osc.
B&W as well as color sets.

may have been mentioned but look for any caps in the boost filter supply to the vert osc plate load cap. think its a .1 leakage here could drop the supply voltage. IIRC there are two one right off the boost the other is upstream a bit, closer to the vert circuit. Again voltage measurement would prob point this out. I use a vtvm for checking.

The plate load resistor of the V.osc is a very common failure. It drifts high due to constant hammering by high level pulse.
Common problem not just in Zeniths but all designs using B Boost to feed V.osc.
B&W as well as color sets.

And drift high it did. Supposed to be 473K, tested at 567K. Picture is much improved, but still has foldover on the bottom. After about 5 minutes of folling around with the adjustments, the picture went somewhat out of focus, and I stopped there.

One interesting thing to note....every time the screen changed scenes drastically (dark to light), I'd lose vertical lock.

After letting it cool down for about 15 minutes, the focus came back. Here's where we're at.....

Have you checked to make sure that the vertical output transformer is working properly? I had a foldover issue with my Zenith 24NC31Z.

I did the resistor check and solder job upside down with the chassis still in the set :)

Think from here I'm going to pull the chassis and start checking all the resistors in the vertical section and ohm out the VOT. I had some time to spare last night, but I didn't want to go yanking the chassis until I get my 730TV2 buttoned up.

Re. the plate load resistor of the vert. oscillator, Kamakiri wrote,
...And drift high it did. Supposed to be 473K, tested at 567K.
Tolerance-wise, that's really not a big drift. It will often increase by a factor of 10 or more, playing havoc with the height and lin.

If you havnt change the integrators. Transformers went but IIRC
you got a very small pix & a resistor burned. 'Lytic in cathode
of vert out also a high fail on any TV, B&W or color. After all
the tests start with caps in feedback loop.

73 Zeno:smoke:

The Vertical integrators here I remember having to replace on my grandmother's Zenith of this chassis. One of them twice. Vertical output transformer shorted out too. That and the caps in the vert section and it ran 9 years, the CRT kicked the bucket. It became my bedroom set. A donor CRT from another Zenith roundie saved it's life. Lasted me until 1990 when I moved. Didn't have room for it.

I was thinking about that too, as I've replaced integrators before. But only with integrators from parts from other sets.

This site shows how they map out, but not wattage of resistor or working voltages....

http://www.boxcarcabin.com/integrator.html

I was thinking about that too, as I've replaced integrators before. But only with integrators from parts from other sets.

This site shows how they map out, but not wattage of resistor or working voltages....

http://www.boxcarcabin.com/integrator.html
1/2 W resistors & 1 KV disc caps more than enuf.......
They caused so much trouble we automaticly changed them
on a "major" job even if no vert problem.

73 Zeno:smoke:

Well looky here!

As I hopscotch my way back through my projects, I pulled the chassis and started checking resistors. Replaced some half watters that were somewhat out of tolerance, then I hit this.

The third color band on the top resistor could be red, could be brown, could be black....but in any event it's obviously been overheated. Resistance on that one reads 4K, so either way it's wildly out of tolerance.

The other resistor appears to be a 22 ohm resistor reading 208 ohms, which is leaving me :headscrat , but in any event both have obviously been overheated and aren't what they should be. I bet these are what got toasted when the yoke failed.

I ordered 5 watt replacements from Mouser, which are en route. Hopefully this is on track to curing the wild linearity issue.

Well looky here!

As I hopscotch my way back through my projects, I pulled the chassis and started checking resistors. Replaced some half watters that were somewhat out of tolerance, then I hit this.

The third color band on the top resistor could be red, could be brown, could be black....but in any event it's obviously been overheated. Resistance on that one reads 4K, so either way it's wildly out of tolerance.

The other resistor appears to be a 22 ohm resistor reading 208 ohms, which is leaving me :headscrat , but in any event both have obviously been overheated and aren't what they should be. I bet these are what got toasted when the yoke failed.

I ordered 5 watt replacements from Mouser, which are en route. Hopefully this is on track to curing the wild linearity issue.

Those are the B+ resistors for the vertical stages. They get burned up when the vertical section develops an overload. They definitely need to be replaced.

On my "M" and "N" Zeniths, the vertical output transformer burned them up. My 25MC33 started with insufficient height and loss of sweep momentarily on bright scenes. It then went to what looked like severe interference and vertical instability and non linearity. That's when the resistors started to overheat. The NC33 just shorted and failed with no warning.

The way those resistors are wired makes it look like you could replace them with a single 1100 ohm 4 or 5W resistor.

My thinking exactly. I just figured that a pair of 2.2K resistors were a lot more commonplace which is why they used them.

I highly recommend you get am ohm reading from the red lead of the vert out to ground WITH the convergence plugged in. should be around 8-10k

Could you adjust the vertical linearity control so the picture just fills the mask? It looks like the linearity was adjusted to compensate for the lack of height.

Can you display a test pattern or crosshatch instead of program video?

That's exactly it. I used the linearity control to get proper height....couldn't do it any other way.

The resistors will be in next week..... so I'll pick it up then and see where we are at. Keep the test ideas coming..... I think I may have nothing to do tomorrow :)

Well, we're sure looking good!!!

The resistor replacement yielded a linear picture. Obviously the convergence is a mile off and the focus isn't what I'd call great. Can't seem to get any color out of the picture either. But hey, progress is progress!

Though the chassis has been recapped, the convergence board is still running the original caps....so that's next on the list before I try to adjust anything.

That's some picture you got there......

.

Nice Job Tim, looks like a great start of a purity-convergence set-up. Just make sure you de-gauss the whole cabinet.

Funny how that set looks "identical" to the one I got a few months back, just has a different chassis, 24MC32.

I plan to send you the vertical output transformer once I bake, re-test and re-varnish it.

Nice Job Tim, looks like a great start of a purity-convergence set-up. Just make sure you de-gauss the whole cabinet.


Would this set benefit (if it's not already there) an auto-degausser circuit? You could grab the coil of wire and its thermistor from most any BPC set and install it in a similar pattern in this set. Would being a delta gun vs in-line gun make any difference?

Got new caps on the convergence board, but the convergence is still off, and I have no color.

I can adjust the red, blue, and green guns and get bright red, blue, and green screens, but no real color on shows. Color killer control does nothing, and the controls on the convergence board itself really don't do anything either.

Advice?

Here's a pic of where I'm at now, obviously I need to tone down the blue drive a bit. And my very skilled 11 year old trainee doing the convergence board caps. That kid is good :)

It is possible the seleniums on the convergence board are bad usually after caps are changed and resistors checked those are next on my list of suspects.

You want to replace them with shottkey diodes. Silicon diodes like the 1n4007 likely will not switch fast enough at horizontal frequency.

EDIT: have you checked the color circuit tubes? On my zenith roundy the color did not work because the tubes were simply dead out of cathode emission.

Ha! Great idea! So often we forget about tubes.....they were tested and good a while ago but it couldn't hurt to check them again.

It is possible the seleniums on the convergence board are bad usually after caps are changed and resistors checked those are next on my list of suspects.

You want to replace them with shottkey diodes. Silicon diodes like the 1n4007 likely will not switch fast enough at horizontal frequency.

EDIT: have you checked the color circuit tubes? On my zenith roundy the color did not work because the tubes were simply dead out of cathode emission.

Tubes are good, and there are no seleniums on the convergence board. What's next I can check?

Tubes are good, and there are no seleniums on the convergence board. What's next I can check?

Does that mean you or someone else recently replaced the convergence diodes? The convergence diodes in all TVs into the 70's were selenium types, though after a while they packaged them to look nothing like the seleniums found in 40's and 50's power supplies that we are used to seeing. The newer packaging did not make them more reliable, and I have had sets as new as 1972 develop convergence problems from diode failure.

As for the color check to see it the 3.58Mhz reference oscillator is running. If so try adjusting the color killer and fine tuning* to see if you can get some color. Also many Zenith roundys had a switch on the color level control to turn off the color if that switch is bad it would explain no color reaching the screen. If all that is good and still no color then grab a scope and start following the color signal from the place the color splits off of the video to the CRT.
*I usually tune the same program on another set and tweak it so that saturated colors show a slight checker board on the monochrome limited set.

When one runs out of possible low hanging fruit trouble shooting, the next logical thing to do is usually signal tracing.

I was wrong! You're right, I was looking for a big sucker! There it is, a little tiny one :)

Five connections on this little sucker too....two of which go to ground. I assume three diodes are needed, and do these little seleniums, when replaced with diodes, require a change in the resistor values? Happen to have a link to which diodes I should use?

I'm fairly sure you don't need resistors in this application.

I don't know what I used last time, but I replaced a part that the sam's says was equivalent to ECG 116, the data sheet of which can be found at the below link.
http://www.datasheetarchive.com/dlmain/Datasheets-X2/DSA879000-31.pdf
A few shottkey diodes that meet or exceed those specks should do the trick.

May sound dumb but is the conv board plugged in ?
It looks so far off that it may not be. Try the center
convergence first & ignore the sides. Then do the sides.
Conv board troubles are almost always broken coils, diode
packs or cooked pots. Only other thing I ever saw was a
few open coils on the clover & cold joints on PCB
built ones.

As far as the no color goes make the set as good a B&W
you can first ! Then deal with the color.

Testing tubes dont always work. No tester will take a 6KT8
and make it oscillate at 3.58 mhz ! It can test good for
emission & shorts but not oscillate..........

keep up the good work.

73 Zeno:smoke:

Got frustrated with this set, and since I now have the CTC-5 and 12, I passed it on to a local friend of mine who is nothing short of a genius with these sets.

It was the wrong damn yoke. That's why it had no color. No wonder.

Got frustrated with this set, and since I now have the CTC-5 and 12, I passed it on to a local friend of mine who is nothing short of a genius with these sets.

It was the wrong damn yoke. That's why it had no color. No wonder.

How can the wrong yoke cause no color. An incorrect yoke would definitely affect convergence.

The color killer/burst gate gets a pulse off of the fly which tells it when to look for the color synch burst. If that pulse is mistimed or otherwise screwed up from a disturbance in the horizontal system those key color circuits will not work correctly.

So guess what's back? :D

And have a few issues. Again :sigh:

First off, the set was working great, and I decided to get it back. Got it home, plugged it in, full raster, but no picture. Saw a wisp of smoke from the tuner :(

Replaced the tuner. Everything worked, but the picture was HUGELY vertically stretched and no color. :wtf:

Turns out that the last owner who I got it back from who shall remain nameless yanked out the oscillator (6KT8) to stick in another set, and since the tube was buried I didn't know it was missing.

:mad:

So now, everything seems okay, but I have vertical foldover at the bottom and to be honest, I'm not sure where to even go with this. I no longer have a schematic for it.....hopefully someone's got the Sams that can point me in some direction.

All tubes are checked, and the set's practically brand new with all the stuff that I've done to it......

Probably no sams, but I should have the Zenith issued schematic. I'll check tonight and post pics if I have it.

Don't have a schematic to look at but I offer this just as a FYI. I had a RCA with a issue like this. ( fold-over and poor range) The Vert height control was fed with B+ on one end and B boost sourced on the other end. The control was open at one end. It appeared to "work" but, the control was open end to end. A replacement did the trick. Good luck

Found the schematic.

https://farm5.staticflickr.com/4681/38925477991_60f89250c6_h.jpg (https://flic.kr/p/22iHfsT)
https://farm5.staticflickr.com/4571/38925473301_5f7badad94_h.jpg (https://flic.kr/p/22iHe52)
https://farm5.staticflickr.com/4583/38038831975_81f3be207f_h.jpg (https://flic.kr/p/ZXmXuB)
https://farm5.staticflickr.com/4538/38925482001_831c8f0645_h.jpg (https://flic.kr/p/22iHgE2)

Can you get one more shot with the circuitry surrounding V22 and showing where it leads on both ends? That's the tube that was missing.

I assume there's no test voltages listed.......

Have you tried resistance measurements? The Photofact has them.
I can email you the Sams if needed.

If you look closely there are DC bias voltages on the important elements of most tubes right on the posted schematic.

https://farm5.staticflickr.com/4597/24099325327_b3f225794f_h.jpg (https://flic.kr/p/CHzkP6)

Have you tried resistance measurements? The Photofact has them.
I can email you the Sams if needed.

That would be great!! I'm more used to using the Sams publications :)

[email protected]

On the vertical issue; Nov 1962 PF reporter special color TV issue noted that thermistor was added starting with the 27KC20 chassis, to compensate for size variation during warm up.

Color: Id check all those peaking coils, and maybe Robert L. Goodman noted this chassis issue in the TAB color manual for Zenith.

On the way.
6 meg file.
Good luck.

After whining and bitching and bitching and whining that I didn't want to get into trying to diagnose it any further (what after all this crap over the years), I got the Sams from reeferman and traced the entire vertical circuit. Tested every component. Nothing.

Then I tested the vertical lin pot, and bingo.....seems that there's something broken off inside that with a gentle movement of the wire, makes the reading go from 1K to about 50 ohms. So that's next.....