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  #16  
Old 09-12-2018, 02:13 AM
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Thanks M

something's goofy in the IF as I wiggled all the IF tubes and the picture came back, I'll check the solder joints and clean the sockets tomorrow, but it's playing fine now.......
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  #17  
Old 09-16-2018, 11:19 AM
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Yaargh! this TV is frustrating...... it seems the vert/horiz is locking but the washed out contrast look goes in and out, but can sometimes be "fixed" temporarily by jiggling the channel selector.

I might try injecting video past the detector diode and rule out any problems there. I'm still thinking the tuner might be troublesome, but the card edge connectors at the back of the PC board might be problematic, but I've cleaned those several times. I have cleaned the tuner, but I've been gentle (maybe too gentile) trying not to screw it up.
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  #18  
Old 09-16-2018, 01:25 PM
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When I clean a tuner I use De-Ox-Id and a white rubber eraser...The De-ox loosens the crud and the eraser gently scrubs it off and polishes the surface...Hasn't failed me yet. There is something nice about seeing a black terminal become completely shiny metal once more.
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  #19  
Old 10-17-2018, 02:33 AM
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Well I feel dumb. I found another 3BU8 (agc keying/sync sep/noise limiter) in my tube stash and swapped it in and the picture is back. I woulda tried this earlier but I hate throwing tubes at a TV set.

The tube tested ok in my tester, but it was slow to get into the green zone
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  #20  
Old 10-17-2018, 10:34 AM
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Quote:
Originally Posted by mr_rye89 View Post
Well I feel dumb. I found another 3BU8 (agc keying/sync sep/noise limiter) in my tube stash and swapped it in and the picture is back. I woulda tried this earlier but I hate throwing tubes at a TV set.

The tube tested ok in my tester, but it was slow to get into the green zone
Sometimes tube substitution is a better approach than testing...I had a CTC-15 clone that had low HV and sweep issues. That set I tested all the tubes, nearly drove myself nuts checking all the passive parts a couple of times, then had it spring to life when I subbed all the sweep tubes from another working CTC-15 clone. Once I narrowed it down I retested the tube and found it still tested good...Buuut if I held down the test button for nearly a full minute it would slump into the bad end of the scale.
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  #21  
Old 10-17-2018, 11:07 AM
dieseljeep dieseljeep is offline
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Quote:
Originally Posted by mr_rye89 View Post
Well I feel dumb. I found another 3BU8 (agc keying/sync sep/noise limiter) in my tube stash and swapped it in and the picture is back. I woulda tried this earlier but I hate throwing tubes at a TV set.

The tube tested ok in my tester, but it was slow to get into the green zone
If you look at the pin-out of the tube in a tube manual, you'll see it's a rather unique design with a few common elements. I don't think it can be checked properly with a tube checker. Best is substitution.
IIRC, the circuit is a Zenith design, as they used it first.
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  #22  
Old 10-18-2018, 05:54 AM
ronl ronl is offline
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Working on tvs/radios...etc since the early 70, s in my basement shop for a large part of my career (made more working for myself)(tough to keep new stocked tubes) i used pretested in tvs or whatever used tubes i knew were good in a set.saved me a LOT of trouble.i would recommend that any tube set every member has in this forum,stock used tubes tested on a tube tester AND tested in your known workining (or once you got it working sets. A lot easier. Maybe this should be a stiicky post. RonL

Last edited by ronl; 10-18-2018 at 06:24 AM.
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  #23  
Old 11-29-2018, 12:29 AM
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Well the sync went funny again. So I pulled the board and found a crack in the ground plane trace around the edge of the board (near the horizontal output tube - high stress area), solder bridged it back and got sync again

The sync circuit must have been dropping the ground there intermittently.

Now the horizontal linearity is a bit off, but I screwed up the noise gate (sync stability) pot so now to fix that.....
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  #24  
Old 11-29-2018, 10:28 AM
dieseljeep dieseljeep is offline
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Originally Posted by mr_rye89 View Post
Well the sync went funny again. So I pulled the board and found a crack in the ground plane trace around the edge of the board (near the horizontal output tube - high stress area), solder bridged it back and got sync again

The sync circuit must have been dropping the ground there intermittently.

Now the horizontal linearity is a bit off, but I screwed up the noise gate (sync stability) pot so now to fix that.....
That PC board job wasn't one of Motorola's better efforts. They made a few years of those and then went back to the hand wired chassis. The tuners were also trouble prone. Yours is probably the last year of that chassis.
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  #25  
Old 09-03-2019, 12:55 AM
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This ol' ball of wax again.

I'm having problems with the horizontal, barely able to hold a steady picture, and I have determined the voltage is too low on the horizontal oscillator tube due to out of spec resistors in the horizontal sweep couplate. I have built simple couplates in the past using perf board, but these are some stacked up monstrosities with 12 pins. Anybody here attempt to make one of these? I'll likely try to build the new ones similar to how the old ones are made.....
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  #26  
Old 09-03-2019, 08:50 AM
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Aah, the mil spec couplates (there is a YouTube video of their manufacture out there), I've never changed one, but I've seen them in gear once or twice, and have a couple nos specimens....it probably has fewer parts than legs which might simplify construction of the replacement.
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  #27  
Old 09-03-2019, 11:52 AM
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Here's a schematic of the two of 'em in this TV. The bad one is the horizontal but I'm going to redo both of them.
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  #28  
Old 09-03-2019, 11:57 AM
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Quote:
Originally Posted by mr_rye89 View Post
This ol' ball of wax again.

I'm having problems with the horizontal, barely able to hold a steady picture, and I have determined the voltage is too low on the horizontal oscillator tube due to out of spec resistors in the horizontal sweep couplate. I have built simple couplates in the past using perf board, but these are some stacked up monstrosities with 12 pins. Anybody here attempt to make one of these? I'll likely try to build the new ones similar to how the old ones are made.....
Have you attempted to replace the horizontal phase detector diodes? Those are easier to change, and could possibly also cause this issue. It looks original in that photo.
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  #29  
Old 09-03-2019, 12:36 PM
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Originally Posted by maxhifi View Post
have you attempted to replace the horizontal phase detector diodes? Those are easier to change, and could possibly also cause this issue. It looks original in that photo.
+1.
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  #30  
Old 09-03-2019, 01:45 PM
old_coot88 old_coot88 is offline
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Definitely replace the dual diode if you got horz sync issues that subbing the tube don't fix.
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