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  #31  
Old 01-30-2015, 07:50 AM
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zeno zeno is offline
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Originally Posted by Zenith6S321 View Post
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
Should be a 103-### on the part. Cross it to NTE. You can get
the specs that way.

73 Zeno
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  #32  
Old 01-30-2015, 10:29 AM
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Zenith6S321 Zenith6S321 is offline
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Originally Posted by zeno View Post
Should be a 103-### on the part. Cross it to NTE. You can get
the specs that way.

73 Zeno
Its a 212-25, the other diodes are 103-###. A google search for "NTE 212-25" did return a "212-25 NTE Equivalent NTE116 1A 600V rectifier,
NTE116 General Purpose Silicon Rectifier 1A 600prv"
I will try 1N4007s. Thanks.

Dave
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  #33  
Old 01-30-2015, 07:09 PM
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One of the three convergence selenium diodes I thought was bad was just an incorrect in-circuit reading due to a coil. Once I isolated that diode it read ok. So for now I'm gonna leave it as is and come back to it later if I have convergence issues.

All the resistance readings checked ok, although I had to reverse polarity on the ohm meter once. I started cleaning the sticky goo off the wires to the CRT, yoke, tuner, and controls. Iso alcohol works well to take it off. After that, next is mounting the patched up HV rectifier socket and replace the bad tubes. Then I can try powering it up.
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  #34  
Old 01-31-2015, 05:14 PM
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Zenith6S321 Zenith6S321 is offline
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The HV socket really had a tight grip on the 3A3, so I bent the socket pins open a bit to loosen their grip in hopes pulling the tube will not break the socket plastic mounts. I had to grind some of the epoxy off of the outside patched up shattered HV socket mounts to get the socket to fit over them. I used new 6-32 machine screws short enough not to bottom out in the plastic. Here is a picture of the socket re-installed. I added some washer because the plastic around the mounting holes was cracking. The 3A3 and the 6BK4 are the original Zenith tubes with dates codes of 62-04. Even though they both tested ok I put in new tubes. I used a 6BK4C/6EL4A in place of the 6BK4.
Attached Images
File Type: jpg HV-Socket.jpg (116.4 KB, 34 views)
File Type: jpg Orig62-6BK4.jpg (119.8 KB, 39 views)
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  #35  
Old 01-31-2015, 05:58 PM
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I powered the set up on the bench without the HO tube and got good supply voltages and some noisy TV audio. I added a jumper to make it easy to check the cathode current on the HO and VO tubes. When I put the chassis back in the cabinet the chassis control shafts did not line up. The chassis control shafts were testing on the opening in the cabinet front and made turning them tough. I enlarged some holes so I could tilt the controls up enough to line up right.

I put the chassis back in the cabinet, reconnected everything and powered it up. Here are some pictures.

Yes we have a raster . Good HV, good raster, good CRT, but I could not get much audio or video. Turning the fine tuning did very little. Seems like a tuner problem.

I unplugged the tuner output and drove the IF with the Sencore VA62 45.75 modulated video and tone. I performed the Sams setup procedure and found the HO cathode current was 210 mA. Sams shows the current should be 190 mA. The horizontal efficiency coil was already adjusted at the dip. I could reduce the current by increasing the HV adjust, but it was 28KV to get it under 200 mA. My line voltage was at 118V, but I have measured it at 125V in the past.
Attached Images
File Type: jpg First-light.jpg (121.0 KB, 34 views)
File Type: jpg ColorBars-thru-IF.jpg (119.9 KB, 53 views)
File Type: jpg HO-210mA-118V.jpg (111.8 KB, 28 views)
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  #36  
Old 01-31-2015, 06:27 PM
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I powered the set through my variac and tried different line voltages and read the HO current. Here is what I got.

At 125V the HO current was 225 mA. At 115V it was 200 mA. At 110V it was 190 mA. The picture didn't change much. I decided to add some dropping resistors in series with the line input. I used four 8 ohm 20W resistors in parallel and mounted them to a terminal strip and the line fuse on the top of the chassis in an open spot. That dropped my 118V down to 111V which gave me 190 mA HO cathode current. The raster fills the screen and I have 25.5kV high voltage. I'll settle for that.

Dave
Attached Images
File Type: jpg HO-225mA-125V.jpg (113.9 KB, 12 views)
File Type: jpg HO-200mA-115V.jpg (112.2 KB, 8 views)
File Type: jpg HO-190mA-110V.jpg (112.6 KB, 9 views)
File Type: jpg DroppingRes.jpg (122.3 KB, 46 views)
File Type: jpg Dropped-7V.jpg (121.6 KB, 10 views)
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  #37  
Old 01-31-2015, 07:02 PM
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I would not be surprised if the original 6BK4 was good. I've seen them work when they had much more x-ray blackening. X-ray blackening is usually a function of run time so I'd guess you have a low hours set.
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  #38  
Old 02-01-2015, 01:03 PM
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When I first tested the set, the fine tuning did not have much effect. I removed the tuner side cover and saw that a plastic gear engages a fine tuning screw on each channel coil insert. The plastic gear had split down its length. A goggle search for 14 tooth 1/4" diameter with a 1/8" inside diameter 3/8" long gear shaft turned up everything but what I needed. I could epoxy it, but that would probably fill up the gear teeth which might cause more splits. If I could find the right inside diameter c-clip/cir-clip I might be able to put it around one end of the gear and fit it into the tuner, but there is not much room in there. I noticed that only about half the length of the gear had dark grease marks on it from engaging the tuner screws. So I'm going to experiment with using some heat shrink tubing to squeeze the gear at the end that does not seem to engage the tuner screws. Here are some pictures of the split gear, the gear with two layers of heat shrink on one end, and with it mounted back on its shaft. The shaft has teeth that engage the inside of the plastic gear. The shaft is driven by the fine tuning knob and the mechanism moves the gear to engage it into the tuner screw teeth. The gear now fits snuggly on its shaft and works surprisingly well, for now...

Dave
Attached Images
File Type: jpg SplitFineTuningGear.jpg (97.7 KB, 21 views)
File Type: jpg GearHeatShrink1.jpg (36.1 KB, 15 views)
File Type: jpg GearHeatShrink2.jpg (37.5 KB, 12 views)
File Type: jpg GearHeatShrink3.jpg (26.4 KB, 23 views)
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  #39  
Old 02-01-2015, 05:11 PM
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I made an attempt modify the broken cloverleaf to get the convergence coils closer to the right positions. I cut the cloverleaf coil support section apart and put springs between them. The put it back together, but its really too floppy and needs more work. I wanted to make an initial attempt at getting some kind of picture. I quickly set purity and convergence. The tuner now sort of works. Here are pictures of the cloverleaf and the first pictures using channel 3 RF. When the set is first turned on I get some color but it quickly fades away after a few minutes. There is also quite a bit of ringing in the video when there a large image contrast changes. I will take a look at it on my scope. Probably will need to do an IF alignment, or maybe its just a wiring mistake I made.

Dave
Attached Images
File Type: jpg CloverleafBefore.jpg (115.2 KB, 29 views)
File Type: jpg Cloverleaf1.jpg (121.2 KB, 40 views)
File Type: jpg Cloverleaf2.jpg (114.0 KB, 33 views)
File Type: jpg FirstPicture1.jpg (116.2 KB, 57 views)
File Type: jpg FadingColor.jpg (115.0 KB, 44 views)
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  #40  
Old 02-01-2015, 05:41 PM
old_coot88 old_coot88 is offline
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I've fixed mucho many of those FT gears that 'd split. Just clean the shaft and gear thoroughly of all grease. Then apply epoxy sparingly to only the splined area of the shaft using something like a toothpick, and slide the gear back on. Never had one fail.

Re. the cloverleaf, back in the day there was an aftermarket item for that, consisting of a bungee sized to fit snugly around the outside perimeter. What you're doing is just as good, probably better.

Last edited by old_coot88; 02-01-2015 at 05:46 PM.
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  #41  
Old 02-01-2015, 06:22 PM
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Zenith6S321 Zenith6S321 is offline
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Quote:
Originally Posted by old_coot88 View Post
I've fixed mucho many of those FT gears that 'd split. Just clean the shaft and gear thoroughly of all grease. Then apply epoxy sparingly to only the splined area of the shaft using something like a toothpick, and slide the gear back on. Never had one fail.

Re. the cloverleaf, back in the day there was an aftermarket item for that, consisting of a bungee sized to fit snugly around the outside perimeter. What you're doing is just as good, probably better.
Thanks for the tuner gear tip!

Dave
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  #42  
Old 02-01-2015, 09:58 PM
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Looks like a decent pic already, I think you'll find the ghosting is an IF/tuner issue. Probably alignment time.
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  #43  
Old 02-01-2015, 10:09 PM
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I wonder if a Velcro strap wrapped around that cloverleaf would hold it in place?
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  #44  
Old 02-03-2015, 06:02 PM
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Quote:
Originally Posted by miniman82 View Post
Looks like a decent pic already, I think you'll find the ghosting is an IF/tuner issue. Probably alignment time.
Yep, looks like most of it is in the IF stages. Here is a picture of driving the tuner input to the first IF with 45.75 MHz modulated with video. And another driving composite video into both the sync video takeoff and into just after the video detector. There does seem to be a little undershoot in the video stages, or maybe just from the unterminated VA62 video signal cable I used. My cheap camera white balance changed colors between the two pictures, it looked the same to my eye.
Dave
Attached Images
File Type: jpg FirstIFinput.jpg (120.3 KB, 36 views)
File Type: jpg VideoIntoE+C.jpg (127.8 KB, 37 views)
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  #45  
Old 02-03-2015, 06:07 PM
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Zenith6S321 Zenith6S321 is offline
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Originally Posted by Kevin Kuehn View Post
I wonder if a Velcro strap wrapped around that cloverleaf would hold it in place?
That would help firm up the angles between the pole pieces. I also see that the green is titled back some. Maybe I need a ring of plastic to hold then in the same plane.

Dave
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