Zenith Roundie Craigslist Score!
 

I've been pretty lucky this summer. First, it was the necked Zenith Roundie with Power tuning I found on the Curb back in June. Today this followed me home:
http://imgur.com/BojudDZh.jpg
It's a Zenith Model 5226UD. It uses a 25MC33 Chassis. The 21FJP22 tests super strong on all guns and has no Cataract or Green Halo! After cleaning a dirty power switch and tuner, I brought it up slowly on a variac.
http://imgur.com/viZBmKeh.jpg
It mostly works. No matter what I do, I can't get the color to pop in. I checked the color killer and the service switch. Pulling the 6EW6 burst amp had no effect on the picture. Are there any common problem areas on this chassis that would cause this symptom? I'm guessing that a loss of Chroma must be the cause. Also, where in the heck are the vert size and linearity controls on this chassis? I can't find them anywhere!
Chassis Shot
http://imgur.com/uHyPdYNh.jpg

As a former owner of that model/chassis here are some tips: The vertical size/lin controls are in the pencil box one is in the hollow shaft of the beige knob left of the green, the other is a hole between knobs.....The fishing lines exiting the yoke are the centering adjustments (don't assume they are garbage and try to rip them out).....On mine most of the tubes in the color section were dead or weak and I could not get any color till I changed them...Test those tubes and replace as needed.

PS the chassis shelf is flimsy; be careful not to rip off the back side of that groove that helps hold the back on.

Oh look. It seems to have the same issue as mine. Stretched at the top and smashed at the bottom.

Must be a common issue on this set. Good to see how all the stuff on the rear of the picture tube is set, though.

From what I've read, this chassis has a vertical integrator like alot of the early 60's B&W Zeniths had. I'm betting that's the problem. First I want to get the color working.

Does anyone have a schematic for a 25MC33 chassis by chance?

Thanks for the tips. I was wondering what that fishing line stuff was, and I would have never guessed that the height/lin controls were hidden like that. Good thing I left those strands of 10lb test alone. I'll swap out the tubes in the color section tomorrow.
I can definitely see what you mean about the cabinet shelf. The chipboard is, well, starting to shed chips, mostly from the bottom. I was wondering if I could brush a coat of heavy duty polyurethane on the chassis shelf to control the problem?

I have yet to learn what the vertical integrators are, or how to replace them. I admit my lack of knowledge in this aspect. I'm hoping reading more and watching posts like this, esp this one, given this is the identical set as mine, will help.

And I have the photofacts for this set. I am not sure how to duplicate it though

The integrators are basically a few caps and resistors in a circuit all encased in one component. The ones I've come across in TV and Audio (Fisher loved them in their tube integrated amplifiers and receivers - Philco loved Them in their TV's) look like a giant, often lumpy square or rectangular ceramic caps with multiple leads coming out.

i saw this set on craigslist.looks like the crt was replaced.glad someone grabbed it.post more pics

Nice score, I those sets.

There is a 100MF electrolytic capacitor connected to the cathode (pin 4) or the 6he5 vertical output tube that is almost always bad and will cause the lack of height. It is usually located on the underside of the chassis at the front. Replace it then do the height and linearity adjustments. This will need to be right before you try to converge the set. Get the black and white picture right before you worry to much about the color. Weak tubes could be a problem for the color, but check the vertical output tube as well and be sure it is healthy.

How does one go about replacing them I wonder? I imagine I could locate them fairly easily, but how do they get replaced? I'm sure their a part thats not easily found.

Most Zenith vert integrators were installed between the synch sep and the input to the first vertical multivibrator tube, and filter horizontal noise out of the synch....If it synchs good leave it be. Some times they also used them in the feedback from the vert output/second multivibrator to the first vert multivibrator section.

Never found a bad Zenith integrator so they would be far from the first thing I'd suspect as the problem. Get the caps and resistors in speck before you worry about it. The sam's should show the way replace it with discreet parts.

There are no integrators on this chassis. I just checked the schematic. So don't loose sleep over them. Do a google search for the chassis and the schematic is online at antiqueradios.com.

I'm going to keep close tabs on this post. His is suffering the same vertical issue mine is.

Mine gets excellent color, thanks to Electronic M getting that part of the set working.

But both this one, and mine, have the identical issue with the vertical.

BINGO!
Today I replaced all the ElMenco, Bumblebee, and other suspect paper caps under the chassis. I also replaced the 100uf electrolytic that feeds pin 4 of the vertical output tube that Bill R mentioned. Bill had it right. A new 100uf cap solved all the vertical issues. I now have full vertical height and good linearity. I still don't have color, despite also replacing all the tubes in the color section with NOS replacements. Where should I look next? The bad 100uf Electrolytic was a cardboard cased Sprague "Atom". Is it just my experience or are Sprague "Atoms" always bad?

Commonly yes. With how old most of them are. The capacitor you replaced was the 100uF 50V in the front of the chassis, C6 on the sams schematic.. It was bad in both of my sets, in one the vertical would collapse under bright images, and the other it would flex and bow.

Replacing it is a must on these.

Mine still has the vertical issue, stretched at the top and compressed at the bottom. I'm working on doing away with C4 entirely, but the caps I ordered got lost in the mail, so I'm suffering a bit of pointless run around.

The color issues might be in your tuner section. There is a very simple way to feed these sets A/V input to see if that produces color at all. I could post a picture from the schematic if interested, or how it was done on my chassis.

I replaced both integrators in my 25MC33. They caused the trouble you have. They are hidden near the vertical output transformer. My service manual is not here but I can look at it this weekend and get the values. They look like three leaded brown ceramic disc capacitors with yellow writing on them.
Check the plate resistor on the burst tube. The tubes can short and draw too much current and burn the resistor.
If you can get a service manual, there are two test points that you have to ground to turn on (defeat the color killer) the color circuit and the other defeats the color afc so the oscillator can free run. If you don't get floating color bars after grounding the test points I would replace the color crystal first. You may need to go thru a couple if the first one doesn't help.
Don't turn any coils unless absolutely necessary. They can get fragile with age.

Yeah I'm worried those are shot in mine, and I'm not sure how to build a new one to replace them. That's why I am watching his posts like a hawk. His set suffers the same issues as mine. He's indirectly printing me a road map what to tackle next.

Watch out for the horizontal efficiency coil near the damper tube. The plastic coil form can break at any time and the turns unravel. My initial fix is to thread some small ty-raps through the chassis to hold it steady in the short term. I might address this in a future post if I find something a bit more professional.

Yes, with the number of newly-acquired Zenith roundies being discussed on here recently, I was hoping someone would address this issue in depth.
The horiz. efficiency (sometimes called 'horiz linearity') coil is a super-critical component that if it fails, renders the whole set unusable.
The failure mode is the coil form itself, which crystalizes with age and breaks, releasing the windings from their sharply-tuned resonance point. With the resonant point lost, the cathode current in the H output soars 'waay out of spec, which will quickly destroy the tube and possibly damage the flyback.

There's an early version of this coil which is OK. The coil form is brown phenolic and does not disintegrate with age. Later versions ARE a problem. The coil form is easily identifiable as an off-white, semi-translucent plastic (nylon?) material. This is the stuff that disintegrates. Anybody with a newly-acquired Zenith roundie should take a look and see which version is used.

Normally the coil is tuned to a sharp 'dip' point, using a milliameter in series with the cathode of the H out tube.

If the set has the 'bad' version of the efficiency coil, there are also three coils on the convergence board using the same material, and are prone to the disintegration problem, but don't render the set unusable.

I was looking at the 25MC33 schematic and noticed that there is a color on/off switch on the color control. I don't remember if it is a push/pull switch, or if it turns on when you turn the color control up. Don't overlook the simple things. I have never had to replace one of the integrators, sets were much younger then. They are just a resistor in the signal line and a capacitor to ground. My Zenith tuners rarely gave any problems and they are among the easiest to clean. Clean the channel strips and be sure the fine tuning system is working. There is a small gear driven slug that is located on the end of the channel strip. I have seen cases where this gets so far out that the fine tuning control no longer moves inside the channel strip. If it gets screwed out to far, it will just spin and not move in. You can get it back in by removing the channel strip and gently pressing on it while turning it to get the screw threads started again. Buy the way Zenith used to advertise the tuner contacts on those channel strips as gold plated.

Gold Guard tuner....

I have a spare hold control with an intact form of the fragile plastic type. I plan to unwind it, take it to a 3D scan/print place to make copies (probably ~12) to sell, and rewind a destroyed convergence coil from another set onto the original form.....Just need life to give me a chance to get around-toit!

Ah, yes - the translucent "natural" colored coil forms that failed - not to be confused with the pigmented white and yellow ones. Miller made the replacements - for themselves and Zenith. Miller used white for themselves, and yellow for Zenith.

Admiral addressed the natural nylon problem in some of their tall chroma coils and transformers - they would break up at the base - we always assumed it was from getting too hot, but they said otherwise - the nylon simply dried out - constant heat and low humidity was the problem.

Funny how Zenith moved from phenolic and fiber coil forms to avoid the seizing problems that plague those materials, and created another more serious problem...

My cool forms are all white plastic. Am I in the clear?

The pigmented white, non-translucent stuff is Okay AFAIK, unless somebody else has experience indicating otherwise.

Here are the integrators from my notes. The number is printed on them. I made mine up from scratch and they work fine. If yours are different, let us know! Oh, both the resistors in the top one are 33K

The no color issue, is most likely caused by a bad Colorburst crystal some are mounted in a glass tube and sum are mounted in a metal can check the schematic it will show you where it's at. Also I suspect you may have bad or leaky caps in the chroma section yet, most times when you have no color or you can't even tune in color you can usually adjust the peaking coils in the chroma circuit slightly and you should notice rainbow bars start to appear keep going until the rainbow bars lock into true color. It's kind of a down and dirty way to do it but techs used to do it all the time why hook up all the equipment when you have a fiddle stick.... also the no color issue can be caused by a dirty VHF tuner

I replaced the colorburst crystal with one I salvaged from a working, but otherwise worthless touchtone phone. I'm storing this TV in an old office building I'm renting and we literally have piles of old phones lying around, left behind by the newspaper that used to occupy it. Nothing old enough to be valuable of course, 90's clones of ATT 1500 series desk phones made by CorTelco/StarTech in Thailand. After soldering in the crystal from the DTMF keypad, I now have rainbow bars. I'm guessing I'll hit the integrators next, and start looking for any other leaky caps in the chroma section. I also recently picked up a working NTSC vectorscope for next to nothing. Would it be useful for this?

Integrators are disc shaped & have 3 wires. Early ones
were dark brown, later ones tan. Part number stats with 87-
The rest of the number is a paint splotch on them. Color
will match the resistor color code. So if you got orange
paint its an 87-3 yellow 87-4 etc. Sometimes the factory
manual or Sams will show the break down of values. If
not there WAS a page out there that listed them all.
Do not confuse them with 3 legged caps that Zenith used.
They were blue or brown & had a 22- part number.

Odds are the crystal is the wrong freq. so DONT go tweaking.
Pull one out of a junker must be a 3.58###.

73 Zeno:smoke:

DTMF touchtone phones have always used the same 3.58XXX reference crystal as NTSC color TV's. I think Ma Bell did that for a reason, touch tone phones came of age at the same period color tv's did.
Shango's page has the integrator values listed.
http://boxcarcabin.com/integrator.html