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  #16  
Old 01-24-2015, 06:03 PM
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Zenith6S321 Zenith6S321 is offline
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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.
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File Type: jpg BrokenSocket.jpg (86.3 KB, 55 views)
File Type: jpg CloverleafBroken.jpg (74.9 KB, 62 views)
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  #17  
Old 01-24-2015, 06:15 PM
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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.
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  #18  
Old 01-25-2015, 05:36 PM
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Quote:
Originally Posted by Zenith6S321 View Post
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.
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  #19  
Old 01-25-2015, 06:26 PM
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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
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  #20  
Old 01-25-2015, 07:17 PM
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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


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  #21  
Old 01-26-2015, 08:21 PM
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I bought a Zenith Color TV Service Manual VOLUME ONE (1973) in hopes it might cover the 29JC20 and have a schematic I can compare the Sams to.
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  #22  
Old 01-26-2015, 08:38 PM
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I was able to fix one of those broken plastic cups with some flex zap (a CA glue that has modifiers in it to make it less brittle.

Its still not as strong as an unbroken one but its ok, just have to be gentle with it.

That Fly looks fine.
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  #23  
Old 01-27-2015, 06:17 PM
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Originally Posted by DaveWM View Post
I was able to fix one of those broken plastic cups with some flex zap (a CA glue that has modifiers in it to make it less brittle.

Its still not as strong as an unbroken one but its ok, just have to be gentle with it.

That Fly looks fine.
That's a relief about the flyback. I already put some Loctite plastic bonding epoxy on the broken HV cup. As long as I never pull the rectifier out I think it will hold...
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  #24  
Old 01-27-2015, 07:07 PM
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Now there is a part that would be a prime candidate for 3D printed reproductions. It's small and the originals were plastic anyway.
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  #25  
Old 01-28-2015, 05:39 PM
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Now there is a part that would be a prime candidate for 3D printed reproductions. It's small and the originals were plastic anyway.
Yeah a 3D printer would be very handy to make one of these. I wonder if the 3D printing materials would hold up to high voltage?
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  #26  
Old 01-28-2015, 05:57 PM
Bill R Bill R is offline
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Well now. I am a field tech for a company that sells and services copiers and network printers. It just so happens that we are going to start selling 3D printers and they will be sending us one for the showroom, as well as sending someone to train us to service them. Don't know when, but this might be a doable project. I will post later when we get it later this year. We have to learn to print something, might as well be a vintage tv part.
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  #27  
Old 01-28-2015, 06:17 PM
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I finished replacing all of the electrolytics. I removed all of the connections from the old electrolytics and mounted the new ones on the underside of the chassis. For now I have wired the caps as per the Sams schematic. The Zenith manual I ordered should be here in a day or two and I will compare the schematics.

I also checked the diodes and found a problem with the three section convergence diode. Two of the diodes read like a silicon diode. The third is shorted. Can I just use three 1n4007s for these? I think I read to use Schottky diodes but I don't know what current or PIV should be. A suggested part number would be great if anyone has had success with it.

Dave
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  #28  
Old 01-28-2015, 06:43 PM
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Originally Posted by Zenith6S321 View Post
Yeah a 3D printer would be very handy to make one of these. I wonder if the 3D printing materials would hold up to high voltage?
If you don't let it print hollow, it should...If not you can always thicken the walls in a cad program, and try again. Those convergence coil frames that like to crack are also prime candidates.
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  #29  
Old 01-28-2015, 09:04 PM
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I've noticed all three of these I've seen pop recently, the clover leaf assy are broken..
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  #30  
Old 01-29-2015, 06:58 PM
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I spent an evening checking the values and wiring for the parts I replaced. I'm glad I did, as I found one wrong value resistor, 1.5K instead of 15K, and two other resistors each with one lead to the wrong solder cup. All the caps values and wiring were ok.

I got the Zenith Color TV Service Manual by R. L. Goodman but it did not have a schematic for the 29JC20. I did have the 27KC20 which has most of the same circuitry for the electrolytic can I was concerned about. The 27KC20 schematic, as well as some information from the Oct 62 Radio Electronics page 71 showing the vertical supply cap as 20 uF, confirmed the Sams values for the four sections of the capacitor. My set was wired as the Sams schematic and parts list section markings, but my cap has the sections with different markings. Here are pictures of the Sams parts list markings of the sections and a picture of my can. You can also see that the 22-3632 can part number matches the parts list Zenith part number. I think my set was wired wrong from the factory. Its now wired as the Sams schematic shows.

Next I'm gonna check the tube socket resistance measurements to see if I messed anything else up.
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File Type: jpg C3-PartsListMarkings.jpg (46.4 KB, 18 views)
File Type: jpg 22-3632-Cap.jpg (108.4 KB, 19 views)
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