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  #16  
Old 04-08-2018, 03:04 PM
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decojoe67 decojoe67 is offline
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Quote:
Originally Posted by jr_tech View Post
Sorry, the antenna terminals are in the upper left, above the power transformer, the terminal strip by the ul sticker is the "sync link" strip, see my previous post.

jr
My bad- I don't have easy access to the back of my set. No, not the antenna terminal. It's above what looks like an antenna terminal near the center of the back the chassis.
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  #17  
Old 04-08-2018, 03:04 PM
Crist Rigott Crist Rigott is offline
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Originally Posted by kf4rca View Post
Vertical oscillator blocking transformer?
Well maybe. It did ohm out good. I have another NIB that I thought I'd try to see what happens.
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  #18  
Old 04-08-2018, 04:28 PM
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Primary to secondary leakage in the blocking trans could cause bias issues...Shorted turns could detune the frequency and suppress oscillation. Did you compare tube/schematic voltages in the vert stage yet?
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  #19  
Old 04-08-2018, 04:45 PM
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Blocking xfmr was my first thought, once he got sweep by injecting at the osc. grid.
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  #20  
Old 04-08-2018, 06:37 PM
Crist Rigott Crist Rigott is offline
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It was the blocking transformer! I had another one here and put it in. Bingo!
Thanks for all the suggestions.
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  #21  
Old 04-08-2018, 07:37 PM
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  #22  
Old 04-08-2018, 07:50 PM
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Can you measure anything odd on the bad transformer? Seems as if we have seen several now that have appeared to be good, but did not function.

jr
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  #23  
Old 04-08-2018, 08:28 PM
Crist Rigott Crist Rigott is offline
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Quote:
Originally Posted by jr_tech View Post


Can you measure anything odd on the bad transformer? Seems as if we have seen several now that have appeared to be good, but did not function.

jr
I measured the leads each other and to the case. Everything seemed good. I then hit it with my heat gun and got this:




Yup, a transformer! I ohmed out the windings again and the values crept up from pri-1130 to 1533, sec-153 to 173. I also checked for shorts between the leads and shorts to the core. All seemed good.
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  #24  
Old 04-09-2018, 12:00 PM
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Wondering if a shorted turn could kill AC operation, but change DC ohms only a tiny amount, so undetectable with an ohmmeter?
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  #25  
Old 04-09-2018, 12:03 PM
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That's what I'm thinking. Or there is some leakage that won't be measurable with a low voltage ohmmeter. You'd need an insulation tester - AKA "megger"
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  #26  
Old 04-20-2018, 09:07 PM
Crist Rigott Crist Rigott is offline
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Well now after getting a decent picture with direct video injection, I can't get a good picture through the antenna terminals.
So I replaced the resistors in the IF stages. The caps were previously replaced. Still not a good picture. I get decent sound though.
So I tried a quick alignment but the signal was very small going through to my VTVM. When I made an adjustment the needle moved just a little bit.
After that I tried it again. No joy. Here is the picture I get of a test pattern. You can see it is there, it just isn't very good. The tubes were tested and they are good.
Any ideas? Thanks.

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  #27  
Old 04-20-2018, 09:29 PM
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Looks like some sort of regeneration (?)
Is this what it looked like before you attempted alignment?
It helps others to help you if you show a picture of the problem before you try to fix it.

Are all tube shields in place?
Could it be an AGC problem?
Sorry for a dumb question, but did you completely disconnect everything you used for direct video injection?
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  #28  
Old 04-20-2018, 09:33 PM
Crist Rigott Crist Rigott is offline
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Quote:
Originally Posted by old_tv_nut View Post
Looks like some sort of regeneration (?)
Is this what it looked like before you attempted alignment?
It helps others to help you if you show a picture of the problem before you try to fix it.

Are all tube shields in place?
Could it be an AGC problem?
Sorry for a dumb question, but did you completely disconnect everything you used for direct video injection?
Yeah, the same thing before the alignment.
All shields in place.
Everything is disconnected.
Actually the same thing before I replaced all the resistors too!
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  #29  
Old 04-20-2018, 09:59 PM
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Warning: I would wait for more comments and ideas from others who have worked on this chassis, but here's my 2 cents anyway.

I forgot there is no AGC, just manual Picture control - I would check the voltages and operation of the control.

Also maybe a bad bypass cap in the IF (all those 1500 pF caps).

Good operation with direct video injection rules out anything after the injection point.
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  #30  
Old 04-21-2018, 09:15 AM
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The 1946-48 630 chassis have a reputation for bad mica caps in the IF...One of the only cases where I advocate recapping the micas.
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