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 Post subject: The bright white line
PostPosted: Mar Thu 31, 2011 9:07 pm 
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The set I'm working on now has the entire vertical stage in one tube, namely a 6SN7. The schematic shows voltage readings for each pin and the ones that don't measure very close are spot-on. There are no resistance measurements given, but I have confirmed that neither the secondary of the output transformer nor the yoke are open. I don't think the oscillator transformer could be at fault as the oscillator section seems to be working as it should. In fact, at the extreme end of the height and linearity adjustments I get about 3/16" of sweep and can tell when the vertical is in sync and sort of make out what's going on. For instance, Ron Reagan was a guest on a show that happened to be playing and his name on the Chyron was legible in a very long, short font.

The classic vertical purr is entirely absent and there's been some mischief concerning the output transformer in the past, somebody having removed it and then snapped one of the mounting screws clean off putting it back. But if it isn't open, what could be its reason for failure?

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 Post subject: Re: The bright white line
PostPosted: Mar Thu 31, 2011 9:34 pm 
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David Roper wrote:
The set I'm working on now has the entire vertical stage in one tube, namely a 6SN7. The schematic shows voltage readings for each pin and the ones that don't measure very close are spot-on.


I dont follow the above the ones that dont measure very close are spot on? so the voltages are ok then, right?

anyway I assume you have tried a new tube, and all the caps have been replaced? esp that coupling cap .25 on the grid of the output side, and the 2.2 meg is not open? Also the eletrolytics have been replaced.


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 Post subject:
PostPosted: Mar Thu 31, 2011 9:35 pm 
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also can you check the boost voltage if its used in the vert circuit.


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 Post subject:
PostPosted: Mar Thu 31, 2011 9:36 pm 
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If either C5 or C3C were open you would have reduced sweep, but not that much reduced. The output transformer could have shorted turns. That could cause the problem. If the yoke had shorted turns, most likely only one of the two coils would have the short. In that case you would still have sweep but with one side of the picture shorter than the other.

Another thing to check. See if someone interchanged the primary and secondary windings.

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 Post subject:
PostPosted: Mar Thu 31, 2011 9:36 pm 
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one more, is there a thermistor in the yoke?

opps never mind, I can see it does not have one on the schematic


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 Post subject:
PostPosted: Mar Thu 31, 2011 9:42 pm 
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a leaky C47 could also kill the drive as well as a open C46. a scope at pin 4 would tell a lot.


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 Post subject:
PostPosted: Mar Thu 31, 2011 9:53 pm 
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Does 8 ohms sound low for the secondary of the output transformer?


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 Post subject:
PostPosted: Mar Thu 31, 2011 10:01 pm 
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Eight ohms is OK for the Vert Out secondary. Disconnect it and make sure the yoke vertical winding is not open. It will be just a few ohms.

Next try momentarily shorting the output cathode to ground. If you get some sweep, check the series resistor (R62) and lin control (R63).


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 Post subject: Re: The bright white line
PostPosted: Mar Thu 31, 2011 10:06 pm 
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David Roper wrote:
The set I'm working on now has the entire vertical stage in one tube, namely a 6SN7.

Minimalist. Dare I ask what sort of TV this is?

Phil Nelson


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 Post subject:
PostPosted: Mar Thu 31, 2011 10:42 pm 
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It's not a Muntz. :) It's a Wilcox-Gay 9V. If you saw the Craig's listing be assured I paid much less than that.

I was able to get about another 1/8" of sweep shorting the output cathode to ground. The vertical winding of the yoke reads much more than "a few" ohms, but I just connected a Tele-check and got the same display on it so I guess that rules out the yoke...? All paper and electrolytic caps have been replaced (in the vertical section anyway) and all resistors more than 10% off.


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 Post subject:
PostPosted: Mar Thu 31, 2011 10:54 pm 
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I just thought of a way you could to a quick check of the vertical output transformer. To do this the audio section of the TV would have to be working. Disconnect the vertical output transformer from the circuit. Using clip leads or some such, connect the primary of the vertical output transformer in parallel with the primary of the audio output transformer. If the vertical output transformer is OK, the audio should be mostly unchanged. It the audio mostly disappears, the vertical output transformer has shorted turns.

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 Post subject:
PostPosted: Mar Thu 31, 2011 11:44 pm 
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Jumper the output grid to a 6 volt AC filament source. If you get a few inches of distorted deflection, the output stage is OK and look for oscillator trouble.


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 Post subject:
PostPosted: Mar Thu 31, 2011 11:47 pm 
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The vertical transformer across the audio transformer does not kill the sound. The primary reads 544 ohms. I noticed that when I disconnect the jumper there is a momentary blip of sweep from the center to the bottom of the screen.


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 Post subject:
PostPosted: Apr Fri 01, 2011 12:00 am 
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I will bet that if you watched the screen while connecting the jumper you would see a blip the other way. That clears both the transformer and yoke. That is a good idea about connecting the 6.3 volt filament line to the grid of the output tube. Give that a try.

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 Post subject:
PostPosted: Apr Fri 01, 2011 12:16 am 
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6.3 vac into pin 4 does not make a difference. I'm not sure I should be so happy that the yoke and output transformer passed scrutiny. After all, what else is left as a possible culprit?


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 Post subject:
PostPosted: Apr Fri 01, 2011 12:20 am 
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Disconnect the yoke vertical and apply about 6 -12 volts AC across the vertical winding. Make sure nothing else is connected. Try the filament source if nothing else is available.


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 Post subject:
PostPosted: Apr Fri 01, 2011 12:20 am 
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Dup


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 Post subject:
PostPosted: Apr Fri 01, 2011 12:47 am 
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Sweep! So that definitely vindicates the yoke.


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 Post subject:
PostPosted: Apr Fri 01, 2011 12:56 am 
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Disconnect the primary of the vert output transformer from the circuit completely, and using an isolation transformer and variac, apply about 70 to 80 volts AC across the primary. Should get lots of deflection if the transformer is good.

Alternately, you could temporarily sub a 6 volt filament transformer for the vert output transformer and see if you get deflection.

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Experience is what you gain when the results aren't what you were expecting.


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 Post subject:
PostPosted: Apr Fri 01, 2011 1:06 am 
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I'm going out for a while, but I will try that when I come back.


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