#16
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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
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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
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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?
__________________
Tom C. Zenith: The quality stays in EVEN after the name falls off! What I want. --> http://www.videokarma.org/showpost.p...62&postcount=4 |
#19
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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
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It was the blocking transformer! I had another one here and put it in. Bingo!
Thanks for all the suggestions. |
Audiokarma |
#21
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#22
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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 |
#23
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Quote:
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. |
#24
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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
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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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Audiokarma |
#26
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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. |
#27
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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? |
#28
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Quote:
All shields in place. Everything is disconnected. Actually the same thing before I replaced all the resistors too! |
#29
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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. |
#30
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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.
__________________
Tom C. Zenith: The quality stays in EVEN after the name falls off! What I want. --> http://www.videokarma.org/showpost.p...62&postcount=4 |
Audiokarma |
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