1966? Zenith Color Tube TV
 

Yet another vintage tv has been acquired by me and saved from the scrap yard. I have not yet found a date of manufacture on the tv yet, but will look closely later. The tv is VERY heavy and big. Was a pain to move but i managed to safely get it moved without necking the crt. Pins are slightly bent on the crt tube but no cracks or obvious signs of trouble.

I am guessing year of manufacture is 1966. Chassis number is either 25MC35 or 25MC36. All tubes are there. Last date of power up unknown. Appears to have never been recapped. I saw some of those annoying and unreliable wax paper caps in there and can already say i am not bothering to power this thing on until i replace the wax papers and do a thorough examination of this thing when I have the time.

The first obvious issue with this tv is a stray inductor having unwound itself and having fallen off the convergence control board. I am assuming replacing this inductor is simple enough once I get a photofact for this thing.

Here are some photos of this tv. Will post more photos later.

https://imgur.com/a/g9762eG

Oh yeah that's a very nice Zenith, I know that one well. Assume nothing with the older sets, as I found out the hard way good replacement parts are not easily found, many of the parts are very similar in value meaning you could sub in the same function coil from an RCA CTC whatever with some creativity and patience. I do recommend replacing the caps in the horizontal efficiency network. Aside from that the motorized tuner can be a pain and I've broken a few convergence yokes in my time on these but overall these are very nice sets.

For date look at date codes on ORIGINAL large parts such as yokes,
FBT's CRT & add a few months to the newest.
Conv coil can be rewound on a fresh form. Odds are the same one out of a junk
conv assy would work to. If it has a hoz eff coil that will be toast too odds are.

73 Zeno:smoke:
LFOD !

M chassis were 1965 model year.

Well, I have begun to clean the tv and do a basic dud test using a multimeter on the tubes, so far all the tubes I am testing at least have a good heater. I do not have a proper tube tester so emissions are unknown. Visually speaking, Horizontal output tube looks baked and probably is bad (heater tested OK), HV Rectifier tube (need to test it for heater functionality still) looks burnt and bad too.

It looks like mickey mouse and his buddies were brief tenants in this tv after it was put into storage many years ago as mouse poop is littering all over the wooden inside cabinet and even some on the chassis. So some cleaning will be desired by me, because I am not a fan of that.

Also of concern it appears after opening up the HV cage area that not only does the HV rect tube look possibly burnt, but I think this thing suffered some sort of arcing. Wire fuse was blown. Flyback does not look melted though as far as I can tell.

Horizontal output tube connector wire is taped up on the other end and goes nowhere...wonder why?

Also looked like some component vaporized when it shorted on that red board. I heard these red boards near flybacks can become conductive and arc too! Very dirty and greasy in the flyback HV cage area in general. Not looking encouraging.

Attached are some photos showing areas of concern along with notes and commentary.

https://imgur.com/a/y4fqXHd

Most old Zeniths FBT's I changed were turning brown at the doughnut.
These were always bad from shorted windings.
The fiber board is mostly for focus & H centering parts. If it has a
stick rectifier they went bad & often took resistors along for the ride.
Arcing can be stopped by cleaning up the area & being sure everything
is A OK. ( an NOS FBT from Zenith has everything used & also the HV rec socket & wiring ).
Your biggest hurtle is finding a hoz out cheap. Most go to hams & the
prices are high:thumbsdn:

73 Zeno:smoke:
LFOD !

So Zenith flybacks usually went bad? I know RCA flybacks had a BAD reputations for failing quickly due to overheating. Is there any way to test a flyback to see if it has a short or other issue. I would hate to recap, clean the tv and get so far only to have a bad flyback take out an expensive tube with it.

And yeah lol I know what you mean about the horizontal output tubes for old tvs. The prices are quite high compared to the other tubes in the tv. The Ford Philco Hybrid tv I was working on had a bad horizontal tube and had to be replaced, seems to coincidentally be a tube that is more likely to go bad first as opposed to others.

I am actually a ham radio operator extra class (Call Sign is KC9IFV) and it is indeed true that high power HF band amplifiers are known to use horizontal tubes (sometimes with some modifications or adapters) as a cheaper alternative to other amp tubes that have become VERY rare like hundreds of bucks. When it comes to high power amplifiers for amateur radio operators, it is often cheaper to buy a tube amp then the solid state ones, if anything beyond 500 watts is desired.

I don't mind coughing up some cash to acquire any tubes as necessary, like with the other old tube color tvs I am working on currently, my main goal is to get them performance to their best potential, and I am ok with parts not being all original.

One other quick question regarding the zenith chassis....is it possible to remove the chassis without removing the tuner assembly? I see some wires from the tuner going into the metal chassis. Not sure if they are hard soldered on or if they are able to be disconnected somehow. I want to take the chassis out to clean it and begin replacing the wax paper caps.

The only Zenith's I know of that are infamous for eating flybacks are the late 40s- early 50s portholes...Zenith learned from those and typically overbuilt their flybacks so they'd almost never fail...Out of the 20-30 Zenith's I've owned I've never had a bad flyback.

You can usually remove the chassis without the tuner there's typically 3 spare connectors on the wires that go to the terminal strip on the tuner (plus the RCA plug for the IF lead at the tuner. The leads are typically pretty self explanatory B+ is a barrel style, heater is flat blade with an insulator on the connector, AGC is flat blade uninsulated...you can mix up heater and AGC but the terminal strip heater lug usually has a dial lamp wire connected to it to clue you in to avoid connecting AGC there.

Typically on Zeniths you almost never need to pull the chassis, just turn the cabinet on its side and open the service saver bottom hatch and you can access everything under chassis with the chassis still in the cabinet...Heck while you're doing that because the CRT is still connected the cabinet will act as its own test jig.

Sometimes the customer controls are hard wired.
Three ways to service
1) test jig
2) flip on side & pull bottom plate. To get at corners remove 3 of the 4
chassis bolts & it kinda swings out.
3) my favorite ! We had heavy roll around carts. that fit a console with 2 feet
extra. Put the right size box there then flip chassis on to it.
We had several crash carts with full Sencore suite to roll up & trouble
shoot.
Most Zeniths had a tuner & control position. Some wires like DGS, SPKR
etc plug onto the solder pots. Usually engraved on chassis or tagged but
good just to remember....

Zenith FBT's did go some but we didnt stock them. Not like RCA's IIRC
we kept 3 different ones on hand.
73 Zeno:smoke:
LFOD !

Minor update. I recently acquired my first CRT tester. It is a Sencore CR 161. From what I have heard online, Sencore is a trustworthy brand. After reading the instructions and manual, I quickly learned how to use the tester. I started using it to test all the CRTs in the tv's I am currently working on including the Zenith tv.

Unfortunately but not surprisingly, the 25GP22 picture tube in the zenith is VERY weak. All three color guns were in the "bad range" at standard 6.3 volts. At 7.3 volts which would simulate a tube brightener increasing the voltage, the green gun went to the weak zone from bad, but red and blue were still bad albeit somewhat improved emissions. The only good news is that there were no shorts.

At this point it is likely a replacement of the picture tube will be necessary. However, I suppose I have nothing to lose at this point by trying to rejuvenate it. I have heard that sometimes CRTs need time to "Wake up" if they have been unused for decades, but not sure how true that is or how much time is really needed to wait.

Good to hear your using that tester on multiple tubes to verify it's operation. This should confirm the Philco tube in the other thread is good.

Yes CRTs can be asleep. With my B&K 466 I wake tubes up by going through the normal test setup and leaving it in test mode on the weak gun(s) for as long as I feel productive...Some tubes wake up in 15min some take over a day.

The good news is if that tube is genuinely weak the 25" and later drop in 23V tubes are fairly easy to come by.

Ok, this is a bit odd. So I was trying to test the CRT for the Zenith again, and let it sit for about half an hour or so and now when going to the check shorts function...it shows the red gun as having a short, although sometimes its both the left and right light dimly flickering or staying solid but dimly, sometimes brighter, or just the left dimly or solidly lit. Are intermittent shorts something that can be created or occur as the picture tube warms up over time?

The tester's remove short function appears to not work and uses the rejuvenate button to initiate it when the dial is set to "remove short" I consulted the troubleshooting manual and and it pointed to capacitor C3 as a possible culprit. I open up the unit and see it appears to be a wax paper cap? If it is wax paper then no wonder the function does not work anymore and it will need to be recapped for the rejuvenate and remove short function to work again. The wires are going straight into this cap and will have to be clipped and then soldered to the new replacement cap.

A bit annoying but at least I found the likely issue with the CRT tester. All the other functions seem to be operating reliably other than remove shorts and rejuvenate.

Here is a photo of the capacitor that I suspect is a wax paper in the CRT tester and will likely need to be replaced.

https://imgur.com/a/T2LYl7T

Hints for delta gun CRT's.
Shorts can come & go. Lightly tapping the neck usually will make them
come & go also. When shorted the raster will take on the shorted guns color
& look smeared as a rule.
Isolation brighteners were available for them.
BUT I would get a raster as cheap as you can before finding a jug.
If you get a full raster you know the big stuff is OK.

Zeno:smoke:

I think I managed to fix the short that I mentioned. I will let it run for a bit again on the tester to see if the short will come back. If the short appears to be gone and removed, then I will probably try to rejuvenate the color guns because all three are in the bad category.

I figure I have little to lose at this point if the CRT is really tired. Of course rejuvenation is risky, it is impossible to know for sure if this crt had ever been rejuvenated before, if it never was my odds are better for the rejuvenation to succeed.

A tube brightener will not do enough to help emissions, I upped the voltage on the CRT from normal 6.3 to 7.3 volts to simulate a brightener and got improvements but not enough to get any three guns out of the bad category.

I believe 8.4V is more realistic for an average brightener, but YMMV.

It appears that I managed to successfully remove the short on the red gun for now. Also successfully rejuvenated all three guns to go back into good emissions range while operating at its standard 6.3 volts.

I have to say I am impressed by how well the Zenith crt handled it. Not sure how long the emissions will stay good like this but if it stays good for the time I use it later then it will have saved me a lot of extra money and work.

Our experience with rejuvving customers' CRTs was very short lived, as they went flat again within a week or two. Then the all-new Beltron came out with a "kinder, gentler" restoration process that held up a little better. But the customer had to understand and sign a No Guarantee agreement. Or as an option, they could choose a brightener which generally gave the jug several months useful life.

I don't have much experience with weak Zenith CRTs before the V types of the chromacolor era, but the chromacolor tubes tended to wake themselves up in normal operation....As in the set will run dim for 2-15min, then get bright and stay bright for as long as it's left on. Then after a couple hours to a couple months off start dim on next switch on. I've also seen chromacolor tubes that test questionable emissions wise and still look fine without a brightener (where other tubes would be dim at that emissions level)....This is part of the reason I hoard CCII CRTs.

I just factor in the inconvenience to using the set and turn it on early.

Good to see the results were positive. A few notes left.
The isolation brighteners I used had an isolation only option.
Newer sets used a different brightener since the CRT F ran off the FBT.
They also had isolate only option. There are other tricks on in-lines
that will even help a soft Trinitron jug look better. Its all about kicking the
can down the street & getting sets picked up.

Rejuve was useful & sometimes a money making racket.
It worked & could get another 6 mo +++ out of a set. We charged an extra fee BUT gave a "coupon" with no limits for a new set of the same size or greater.
Basically it was " make your best deal THEN hand this to us & we will refund
the rejuve fee". It worked quite well.

73 Zeno:smoke:
LFOD !

We tried one once for H-K shorts, and it blurred out fine detail in the pic due to parasitic capacitance between the windings. This was on a color roundie.

There's often a heater series resistor of maybe 2.7 or 3.3 ohms (located on the neck board) that you can shunt. Does same thing as a brightener.

Finally mustered up the patience and time to finally pull the chassis out of the Zenith. I more thoroughly cleaned it up as well as the inside cabinet. I used deoxit on all the pots. I am going to replace all the electrolytic capacitors, paper in oil caps, wax papers, wax paper safety caps ect. I even found at least one bumble bee cap and a sprague black beauty. I ordered the replacement capacitors needed from Digi key and am waiting on those.

Also checked on the bulb near the tuner and surprised to find that it is not burnt. I also plan on testing all the diodes in circuit using a multimeter. Will check thermister, flyback, and other transformers.

Oh and I somehow managed to find and buy a NOS Thordarson Vertical Output transformer for this tv. So if that transformer is bad or does go bad I will be ready for that.

I already clipped out two wax paper caps to examine more closely and made note of their location. Also will be needing to get a replacement inductor or two for the convergence board that is screwed on the top part of the wood cabinet as the plastic is literally turning to dust and falling apart.

I am planning on doing a full restoration of this tv to look like new in performance. I will even eventually work on restoring this wood cabinet. Cataracts look minimal on the screen. Speaker fabric grill needs replaced as it is all chewed up.

Two wires got pulled off and will need to be resoldered but that is no big deal.

Taking this apart today gave me quite the workout. lol

https://imgur.com/a/jRTnZ2V

I hope you get this Zenith TV working as well as it probably did when new. Zenith has always been my favorite brand of TV, even after the DTV transition and Zenith's move to Korea from Chicago in 2008, so when anyone here on VK talks about one I will read the post with great interest.

BTW: How did the speaker grill on yours get so chewed up? You didn't mention pets, etc. getting at the fabric and chewing on it (cats will often do this, as well as chewing on wiring; I had a cat several years ago that chewed through the insulation on my computer's printer cable and, needless to say, destroyed the cable in one fell swoop), but it can happen, as my note in parentheses stated. It is fortunate your TV's speaker cone and/or the wiring to the speaker wasn't damaged by whatever chewed on the grill.

Hard to say exactly why the speaker grill was chewed up. My best guess is rodents. As there was rodent poop in the wooden cabinet of the tv where mice took residence at some point in the past.

I got this tv from someone who had worked at an e waste center, they did not have the time or interest. So while this tv is in rough shape, at least I managed to save it from the landfill.

I also noticed the HV area was just coated with tobacco tar and nicotine glaze. I know most people smoke back in the 1960s so I was not surprised to see evidence of the prior owner being a smoker but was in awe at how much gunk built up. I guess smoking probably caused a short in the HV area at some point.

So you can call this Zenith a smoker's choice set!

Brief update: I also now acquired a NOS flyback transformer for the Zenith!

Chassis has been thoroughly cleaned with a toothbrush to help loosen up residual dirt, all tubes have been tested with multimeter for a basic filament test already, sockets cleaned.

Diodes have all been checked out and tested and appear to be ok. Some weird looking tophat shaped diodes are on this chassis. I guess these were a thing once upon a time. Also some normal glass package germanium diodes, along with fairly normal looking diodes.

Still unsure of the exact reason this tv was no longer being used ages ago but clearly has something to do with the HV and horizontal output tube. The 6JS6 tube does look a bit used visually but I do not have the a tube tester atm to do anything more than a filament test. It is quite possible though that the 6JS6 tube may have failed in this tv. It would hardly surprise me since it is common for horizontal output tubes to fail in tvs directly on their own from use or as a consequence of something else failing.

My current guess is still tobacco smoking contributing to tar buildup in the HV area which likely caused arcing.

Next step is to use a dremel that I recently bought to saw off the can caps, leaving terminals in place and recapping. Also will have to check the transformers including the flyback with a multimeter eventually.

Unfortunately three coils basically adjustable inductors had the plastic cracked due to age. L40, L41, and L42. They are all for Dynamic convergence. Any ideas on where to find replacements for these? Do they even make them anymore with these range of values?

Also found a date inside the cabinet along with some random number.

September 21, 1965

1 4 6795

Any idea what that string of numbers means?


https://imgur.com/a/yZrbeLP

Update: Zenith chassis fully recapped, all waxpaper, paper oil, and electrolytics replaced and put in and checked. Flyback winding for HV rect. tube cup and horizontal output tube cup tested ok, will test remaining windings and transformers soon. Cleaned chasses more, deoxed all pots and cleaned tube sockets, all tubes tested and some are weak but none straight up bad or with unacceptable leakage or shorts. Likely the CRT just got so weak that tv was put out of service for that reason. Also the CRT having a short on the red gun was probably the straw that broke the camel's back and put it out of service too. Like mentioned before, it appears the rejuvination and fixing of short was successful, only time will tell if it holds up for long when put back in service later down the road. Diodes checked out ok.

Found all three needed replacement inductors for dynamic convergence board L 40, L41, L43. Replacements are all NOS and will be installed soon.

Accidentally cracked the burst amp inductor on underside of chassis. Ferrite core was unharmed though, one of the wires pulled of a post and is now too short to reach. Repaired the plastic crack on inductor but wire still needs to reach post...ordered a NOS replacement for this inductor in case I need it...price only $15 plus shipping lol. And like I said before even IF flyback and vertical transformers were toast...I have NOS replacements for those too ready. So I am sure this TV will have a new lease on life but the tobacco tar fumes may be a bit...off-putting for some.

Any tips for fixing an inductor whose wire is too short to solder back to post? can I just patch it in with another wire of make the metal connector post longer?

Just bridge it with another piece of wire. Try to keep guage similar, and try to avoid excessive lead length.

tech topics
 

Coils
You can rewind coils onto another form. All Zenith conv
panels through the hybrids used them. Swap the slug too !
Panels have a S-##### number that may have a sub. I can look those
up.

Rejuve
Kicks the can down the street. Gives the cust time to save up
the $600 +, a LOT of $$$ back then. Using a modern B&K
or Sencore is best on clean & balance. Heavier settings are
last ditch. Results seem best when you get lots of needle swinging
& flashing in neck. Unpredictable but can stretch things a few
years at times.

Zeno

Thank you! That was what I was thinking I could get by with doing but just wanting to verify before I made another goof up. I luckily so happen to have some wire of that gauge roughly, it is known as "wire wrapping wire" which also tended to be the gauge for some fuse wire I needed when replacing the wire fuse on my old motorola tv way back. I will compare and see how close the gauge is or if needed I will simply get some more fine wire. I did manage to order a replacement NOS inductor specifically meant to replace this one on the zenith luckily...price $15 plus shipping lol. I keep lucking out with this tv when it comes to replacement parts really.

First I manage to somehow get a NOS thordarson flyback for this tv...then a vertical output transformer NOS thordarson brand....then I got all 3 inductors that I needed which had broken due to old plastic cracking on the dynamic convergence board...and now this inductor lol. This tv is getting five star treatment by me. XD

From what I read online the filaments of the older CRTs from the 60s and prior tended to be thicker and more rugged due to the filament being thorium based. I definitely saw quite a bit of sparking and flashing when doing the rejuvination at the time. It was a situation where I had nothing to lose because this CRT clearly had been used ALOT and the chassis's dirtiness testified to this. I always wonder if there would be any money in rebuilding old CRTs again, i mean if someone got into that business they would be the only one in the whole world doing it.

Also, I realized this tv chassis has a "stick" style shaped recitifer diode known as GECR-1. These apparantly are known for failing thus I will be replacing it as well while I am at it.

Also question regarding L 40 and L 42 adjustable inductors on the dynamic convergence plate on back of tv. The sam's photofact schematic does not show dots for the inductors but instead three horizontal lines with a downward diagonal line arrow one the right of each of those inductors. What direction are they supposed to go? The NOS replacements I got are not as obvious as the original zenith branded oem ones. From what I understand inductors do not have polarity per say but can influence polarity?

For one coil inductors, really don't made a difference in adjusting (results/value depends only about the slug position), unless if have a PM like linearity control, but makers for sure padronize positions/connections, to facilitate assembling and helping QC.
EDIT: in some secial cases, with crammed circuits and coils very close, is good to follow the original position, due to cross coupling/leaking magnetic fields, but I'm pretty sure that in a normal TV this cannot be a issue for these circuits.

That is good to know. I was worried about this being an issue. Either way I will be prepared and will be testing the tv not too far off from now. Zenith tvs of this era had a pretty good reputation for reliability

Update: I have decided to remove the old flyback as it looked quite dirty and the rubber tire was hard as a brick due to high hour use and may have had arcing issues before. Cracks are visible as well. Will keep it for future repair. I am going to install a NOS Thordarson flyback for this tv like I did for my Ford Philco tv already. I might as well since I want to make sure this tv will be in top shape for many more decades of use and service.

Does anyone know what modern common diodes I can use to replace a GECR-1 stick rectifier diode?

Focus rects were usually on the replacement along with other stuff.
We always used the Zenith replacements.
The rect is common & was sold by ECG, SK, GE etc...
Google it.

Zeno.

It's kinda wasteful to replace a good working flyback because it doesn't look good. There's not a limitless supply out there.

I've seen mint looking flybacks be dead and I've ran destroyed looking flybacks for years.... Electricity doesn't care what the path looks like as long as the path functions.

Flybacks and HV cups clean up nicely with off the shelf rubbing alcohol, and tougher dirt can be removed with spot treatments of Goof Off....Heck severe carbon tracking can often be permanently cured by Dremeling out the carbonized bit of insulation and replacing it with silicone caulk.

agreed, very wasteful

a bit of corona dope works wonders

before.
http://suzaku.live-evil.org/0716221404.jpg

http://suzaku.live-evil.org/0719221857.jpg
after.

from my hoffman colorcaster television
working fine for over a year now,