1963 Zenith 29JC20 restoration

[Zenith6S321]

Originally Posted by old_coot88

From the photo, it looks like the coil form is phenolic. If so, you're in luck. The whitish, semi-clear plastic forms are the ones that crystalize.
If the three blue adjustment coils on the convergance board also have phenolic forms, you're doubly in luck.

Yes the convergence board coils also look the same. From a couple of tags on the set I think it was made in 1963. Maybe Zenith changed to phenolic coil forms by then.

[Electronic M]

Originally Posted by Zenith6S321

Maybe Zenith changed to phenolic coil forms by then.

It is the other way around. The phenolic forms are the old type, and Zenith moved away from them to the notorious plastic forms that they had from the mid 60's to the late 70's.

[Zenith6S321]

I tested the coils today and I think they are all ok. There is some wax on the bottom of the HV cage but the flyback otherwise looks and tests good. I'm not sure how concerned to be about the amount of leaked wax. The flyback shows 16 rings on my Sencore LC75. The 3A3 plastic socket cup is broken but I think it might be fixable. The cloverleaf has split and looking back at the service tag it lists a 43-473 which is the part number for the cloverleaf. So this set has had two of them and I guess both broke. I wonder if separating the cloverleaf into the three sections at the place where the plastic springy area is and then using an actual metal spring between the section could work.

[Zenith6S321]

I spent most of the day checking the resistor values and replacing the ones I thought were too far off. The Zenith solder cups makes it easy to lift one end to check values. I replaced all the resistors that were beyond or close to their tolerance band allowance. That ended up being 40 resistors. I like to replace resistors with higher wattage replacements, like 1W where there were 1/2 W. Next are the old non-ceramic capacitors and then the electrolytics.

[Carmine]

Originally Posted by Zenith6S321

I spent most of the day checking the resistor values and replacing the ones I thought were too far off. The Zenith solder cups makes it easy to lift one end to check values. I replaced all the resistors that were beyond or close to their tolerance band allowance. That ended up being 40 resistors. I like to replace resistors with higher wattage replacements, like 1W where there were 1/2 W. Next are the old non-ceramic capacitors and then the electrolytics.

Out of curiosity, how many resistors were bad and by how much (worst case)?

I also have one of these sets, so I'll be watching.

I notice two holes punched in the tuner bezel... Does this have an optional UHF Tuner? If so, I've never seen them arranged side-by-side on a Zenith roundie... Usually it's diagonal.

[Zenith6S321]

Originally Posted by Carmine

Out of curiosity, how many resistors were bad and by how much (worst case)?

I also have one of these sets, so I'll be watching.

I notice two holes punched in the tuner bezel... Does this have an optional UHF Tuner? If so, I've never seen them arranged side-by-side on a Zenith roundie... Usually it's diagonal.

Worst case resistors were (Sams numbers) 470K ohm R184 was 950K ohm, 470 R82 was 1084, 22 R39 was 36.1, 22M R129, R130, R131 were 30.3M, 30.2M, and 32.5M. The rest were over, at, or just under their tolerance above their design value. I wanted all of the resistors to be within their tolerance, figuring they specified that tolerance for a good reason. I did find one bad factory solder joint on R158 that made it read open when checking between leads of the parts it connected to.

Yes this set has a UHF tuner which mounts to the right of the VHF tuner (when facing the front of the set).

Dave

[Zenith6S321]

Today I replaced the caps that were not mica, ceramic, or electrolytic. The Sams photos show bumble-bee (black beauties?) where my set had mainly Sprague orange-drops and brown-drops plus a couple of other tubular caps. I think the cleaner looking orange-drops were recent replacements as most of the orange-drops had a dirty film on them. Most of the orange and brown drops had leakage of around 1-15 uA at their rated voltage and some measured outside their uF tolerance, .0068 C46 was .0087, .15 C6 was .206, .056 C129 was .0647, and a couple caused my Sencore LC75 to not read properly even when out of circuit. I replaced them all with in tolerance valued capacitors, not wanting to trust 50 year old caps.

I started the first of the three multi-cap electrolytic can capacitors and found that the section labeling (square, triangle...) on my capacitor can does not match the Sams, but the chassis was wired as the Sams shows. So my capacitor values do not match those shown on the schematic or the parts list. I don't think this is a Sams mistake, for the following reason. The Sams schematic shows C3C as a 4 uF 150V cap with a blank label marking. The Sams shows that section wired as the cathode bypass cap of the V7 AGC tube with 35V across it. My set does have the V7 AGC tube wired to the blank labeled section, but in my can that section is a 40uF 25V cap. Which puts a 25V capacitor where Sams shows 35V. Here is what the Sams schematic and parts lists as the sections and what my can has:
Section Sams My set
A (square) 50uF 450V 20uF 450V
B (triangle) 40 uF 25V 4 uF 150V
C (blank) 4 uF 150V 40 uF 25V
D (1/2 round) 20 uF 450V 50 uF 450V


Ok, what am I missing here? Is it just a Sams error? But if so, then why does my set have a 40 uF 25V section connected to the V7 AGC cathode which Sams shows at 35V, unless that Sams measurement is wrong....

Also, Sams shows the 50 uF on the screen of the audio output tube, but the 20 uF on the power input to the vertical output transformer. Wouldn't it make more sense if the vertical output transformer power had the 50 uF and the audio output had the 20 uF? Should I just wire it as original?

Dave


Dave