1966? Zenith Color Tube TV

[Lain94]

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

[ARC Tech-109]

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.

[zeno]

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
LFOD !

[Electronic M]

M chassis were 1965 model year.

[Lain94]

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

[zeno]

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

73 Zeno
LFOD !

[Lain94]

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.

[Electronic M]

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.

[zeno]

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
LFOD !

[Lain94]

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.

[Electronic M]

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.

[Lain94]

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

[zeno]

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

[Lain94]

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.

[Electronic M]

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