Zenith 5311U / 24MC32 restoration
 

Yes, I finally got myself a roundie courtesy of drh4683! I figured I needed a new color TV to go in my new house :yes:

It's a Zenith model 5311U with a 24MC32 chassis he scored at an estate sale.

He said it does not work (no B+) but the original 21FBP22 tests strong.

It has a vinyl clad metal cabinet and looks to be in very good, all original condition.

Here's are some photos from the ebay listing and it arriving in my garage.

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I was wondering when we'd see you restore a color roundie. Very nice set Bob. :tresbon:

Oh oh. I see a possible new collecting addiction coming on. Good thing you have the bigger house. :D That's a very sharp looking set.

Callin Caps, Integrators, Elmenco Tubulars, oh my! I wonder which you will encounter......:D

Great set there Bob. Put that on a custom dolly and wheel it into your new kitchen. Nothing beats a Zenith color for cartoons over breakfast :D

Ahh, so you won that set. That era of zenith, assuming the tuner/IF are good, are real easy to fix and usually rather reliable.

The very first thing I would do is verify that the H efficiency coil is intact. The coil form tends to crystalize over time which lets the windings go loose, detuning the coil. If that happens, you can't tune it for the required 'dip' in H output tube cathode current.

The coil form material that's most often affected is whitish, semi-translucent plastic. If the coil form is brown phenolic, yellow, or solid opaque white, it's probably OK.

If the eff. coil is busted it renders the set dead in the water until replaced.

Thanks for the tip. I dug out this Zenith service manual I've been lugging around since the 80s and found the schematic. Crazy that I've had it for decades and finally have a use for it!

Not sure which is the efficiency coil. Where does it connect in the circuit?

https://flic.kr/p/Sd19Bu

I see, some hack left off the X-ray cage around the 6BK4! It also has the GVG tuner. I would've bet it had the Oak or the standard Coil. The base models usually did. It also seems to have a 21FB with a separate safety glass, which is great with me! :thmbsp:

Usually in the plate circuit of the damper tube, but I don't think your chassis has the adjustable coil. I have the same Goodman book and they don't show it on the schematic. If you look at the schematics prior to this chassis they have the coil labeled as such.

On Zeniths of this vintage that I've seen, the eff. coil is usually mounted in one of those holes in the rear chassis apron, on the far right end. It's 'snap-in' mounted from inside the apron, with the end of the form protruding out. The slug is adjustable from outside with a 'diddle stick' tool. If this set doesn't have one, I'll hafta add this to my "learn something new every day" list.

On some makes of color TVs the eff. coil is labeled "linearity coil"

Bob, Glad to see you got that set. I bid on it the first time it was auctioned. Seems the previous winning bidder didn't notice the words ' Local Pickup Only ".
I ended up buying a color roundie in Michigan that week. I used to watch BOZO at a friend's house on a 1964 Zenith Roundie.:thmbsp:

Very nice set. Will have an almost unbeatable pix in
a dark room with early content such as Bonanza. I
had one in my bedroom (12X10' !) in the early 70's and
would watch things that sucked just for the realistic color.
Fun to work on too ! You do have to watch the H. eff coil
or you will be buying expensive H outs.......

73 Zeno:smoke:
LFOD !

I have an identical set in appearance, with the exception of the U.H.F. tuner. Also, my chassis must be some other run as what I see around the HV area is configured differently. If I was home I could give my chassis number, but probably not important. My efficiency coil was the first problem I noticed when I got mine and a replacement was almost impossible to find. I finally did get one and was advised to open the cathode of the H.O. tube and insert an ammeter to monitor cathode current and set that coil to something like 200mV. in order to NOT burn up the flyback.
That was a few years back. I wound up having to run the set on a variac at a slightly reduced voltage in order to keep the cathode current where it should be. Probably just leaky caps in the H.O. circuitry. Other than that, the set played well enough and produced a decent enough color picture needing what looks like some dynamic convergence work, which I have never done myself. Frankly, and sadly the set has been put to the side due to the introduction of a woman in the home. LOL! Together we simply just had too much stuff & it was/is in the kitchen surrounded by stuff. No way to pull the chassis and change the caps. Now I actually have my room back, but thus far have no plan of restoration. I’ve regressed back to radio interests and vintage test equipment. Smaller and easier. I may wind up letting it go.
This set Banderson got looks like a very nice set, and although most of the posts here seem to be about RCA sets, these Zeniths are supposedly better built and more reliable. Good luck with the set and don’t burn that flyback!

The 24MC32 and mid-65's 24NC31 was a departure from the 25MC30 series and earlier roundy zeniths. It was more compact, having the HV cage on top of the chassis rather than beside it.

"learn something new every day" - Old coot, you also never stop seeing new (to you at least) Zenith sets on this forum.

I think you guys are referring to the coil on the plate of the damper tube ? It doesn't appear to be adjustable.
https://c1.staticflickr.com/1/623/32...4cd97f9c_z.jpg

I have a nifty SECO HC8 cathode current monitor I can use.
https://c1.staticflickr.com/4/3783/3...89e4ec71_z.jpg

This is the 25LC30 circuit everyone's been woopin' and hollerin' about ;)
Looks like you could add in your own horizontal efficiency coil.

http://i452.photobucket.com/albums/q...pses52ugfv.jpg

Thanks. Looks like I have the simplified design. I'll see about adding that in when I pull the chassis. Wouldn't be surprised if there's space for the extra components.

Get rid of the R35, while you're at it. It's a common failure item and not needed. 1500 ohm, 1 watt.

Isn't that suppose to act as a current limiter in the event something goes terribly wrong?

Zenith engineering recommended eliminating it. It was the subject of a thread, quite a while ago. :scratch2:

At first, I thought you found the very same model I have, only realizing that mine has a wood cabinet with its front legs consisting of extensions of the front face of the cabinet continuing to floor level.

I had been working on it, after gathering a new tube for every tube except the 21FJ (which tests good), but there had been a lot of nonstandard work under the chassis, and something went "pop" one night I was testing it out.

It's quite compact for a color roundie with legs. I think I can say with certainty that it is the only color roundie that has ever been transported in a Prius.

Robert Goodman also says to get it out of there.(Zenith Color TV Service Manual,Vol I,Tab Books) Same book Bandersen showed us earlier. Robert mentions a couple different situations, which at first impression leads one to believe he's talking about two different resistors, however there only seems to be that one 1.5K associated with the HV?

http://i452.photobucket.com/albums/q...psvrlzjd4n.jpg

Thanks for the info. It'll be interesting to see if that resistor has been removed or jumpered.

Yep, my resistor popped under that rectifier. The socket was also burned which is why there was an annoying hissing before the repair which was replacement of the socket and jumping the pins where the resistor would have been. This is a good thread! It's making me think of working on mine again.

I got a copy of the Sams I'm itching to pop the back off this set, but I've got a ton of post move stuff to do first including setting up a new workbench.

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I popped the back off last night and took some more pictures. I like how the back is held on with clips rather than screws. Very easy to get on and off.

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So far I see a mix of bumblebee and maroon caps.
I assume the bumblebee are paper inside and should be replaced but what about the maroon type ? Are these plastic film and generally OK or should I shotgun them ?
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Also any thoughts about the missing x-ray shielding ? Would some galvanized or aluminum sheet metal be sufficient ?
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The Maroon Elmencos can stay - they are film, just like an Orange Drop. RCA and Zenith loved them - I've never seen one go bad.

As to shielding, any ferrous metal will work - I've used perforated (1/16" holes) metal before - came straight off of an old Phase Angle Voltmeter. Also, make sure you have the 6BK4C regulator, or a 6EL4A. They are the regulator tubes with the longer anode that provides the optimum X-ray protection. Of note, patented by a female RCA engineer!!

Thanks for the tips. It does have a 6BK4C/6EL4A installed :)

A friend stopped by over the weekend and we organized the basement a little. It's not much of a workbench, but this card table is a start ;)
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After getting his Farnsworth radio working, I figured why not take a whack at this Zenith?

Doug said he had tried powering it up and there was no B+. I hooked it up to a Sencore PR57 so we could monitor the current draw and turned it on.

The tubes lit up but no B+. I gave the circuit breaker a couple nudges and viola - power. A few moments later, the tell tale crackle of HV and a raster :D

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That was quickly followed by a lighting show around the CRT anode lead. I moved some wires out of the way and that mostly tamed it.

Now we still have an analog OTA LP NTSC station on channel 6 and it's very handy for testing. Try as we might, we got nothing.
There was some noise and static as we changed channels, but no hint of reception. So I dug into the tuner to swap out the tubes.

While doing so I noticed some bits of wire dangling from what I think is a CRT grounding wire :scratch2:
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Anyway, after some cursing I managed to get the two tuner tubes swapped out. The dial lamp is out too, but I'll save that for another day.
Is partially visible in the bottom-right. Is there any easy way to get at it ?
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That did the trick! We had great sound, but a horribly out of focus picture. The focus control had no effect.
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Seemed like the obvious thing to do was replace the 1V2 focus rectifier. Bam! We had a sharp, bright image, but no color.
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A little control adjust took care of that :banana: Not bad for basement reception of a low power station using a scrap of wire for an antenna!
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The HV arcing happened a few more times while swapping the tubes so I wedged in a gob of HV putty.
That helped a lot but there is still the occasional hiss and whiff of ozone.
Seems to me the HV cup and anode wire are a little on the skimpy side. I'll be replacing them eventually.
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All in all not bad for a first power up. Don't recall ever having a set come back to life so well just by replacing a few tubes.

That is a Zenith for you!

You SO make me want to take on my 5317U again, but I have several things ahead of it.

The dial bulb might be easier to access from the front of the set, by removing the knob.

I tried that but didn't see any obvious way to get the bulb

The socket might be on a slide on-off mounting.

You might want to simply pull the VHF tuner. Zeniths (at least the B&W ones) had the VHF tuner mounted with two screws in the cabinet back. I see what looks like rubber grommets on the side of the VHF tuner mounting bracket interfacing with pins on the front face plate.

I tried getting at it from the front and the knob came apart :(

I think the smoked plastic goes towards then then white paper then the clear plastic then the black ring :scratch2:
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After a bit of poking around, I realized the bulb holder slid off pretty easily. The holder clip is the ground and the wire clips onto the tuner.

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https://c1.staticflickr.com/4/3844/3...e3db24ba_z.jpg

It appears to be a #240 bulb - 6.3V @ 0.36A.
Specs: http://www.taillightking.com/images/...0240%20USA.pdf
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All I had handy was some #1847 (long life #47) and an LED equivalent. They only draw 0.15A and I expect are not as bright.
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It works but is really dim.
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I noticed the width slowly expands over several minutes when the set is first turned on. No doubt it's the old caps reforming.
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Zentih sure went cheap on the control door.
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All the controls appear to be working correctly. Going to put together an order, get some new caps and pull the chassis soon.
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Be careful with that knob - that pot metal "cage" liked to break. I broke the one on our neighbors' Mother-in-Laws set....

https://flic.kr/p/Td3QqK


Cheers,

When I restored my 25MC33 Zenith roundie ten years ago now, I too had the tuning knob come apart. The two sections are just lightly crimped together. I had to use some JB Weld to make a more permanent fix. The channel display looks about as bright as mine does with the correct lamp. These are not very bright. I love the metal cabinet. I wish mine were in a metal cabinet. They are more compact and less prone to nicks and scratches. They are great sets and the color is unbeatable when everything is working right.

Thanks for the info :thmbsp:

I hooked the set up to a converter box and watched a little MeTV tonight. Definitely an improvment over the weak OTA reception! There vertical height is a little lacking and horizontal hold is at one extreme. Also some streaking when text appears. It ill be interesting to see how things change after a recap and weak tubes are replaced.

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