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#1
05-23-2010, 08:41 PM
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smear
My latest project is a RCA 14-s-7052 (sam's set354 folder 16). The picture is ok but has smear, both white to black and black to white.What causes this ? As always the set has nos tubes that have been checked and rechecked and paper caps and electro's have been replaced. The B+ is within 5 volts of the diagram and the voltages around the video IF and vid-output tubes look close enough. The contrast control can get rid of the smear but then the pic is more gray than black and white. Not knowing if it is a mistake I am trying to set the contrast the same way as my other tv, so I am not sure if this set is not capable of a strong contrast. Any Ideas?
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#2
05-23-2010, 08:49 PM
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guessing here
open peaking coil weak video detecting diode (if used instead of tube) weak video coupling cap IF alignment. I seem to recall those as possible candidate from what I have read/seen. can you feed a composite signal in at the grid of the video amp? that would get narrow it down to after the video detector at least.
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#3
05-23-2010, 09:35 PM
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Thanks, I will check those.
The detector diode is new, The alignment does affect the smear in this set but it should be calibrated correctly( if I did it right!). I will recheck though. Can I feed a signal in?, I do not think I have any equip. to do that.
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#4
05-23-2010, 09:44 PM
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do you have a dvd player or converter box? all you need is an RCA cable connect the outer shield part to the chassis and the inner to the grid. use the video out. the audio will not work of course but you will be able the check the video
Before you make this connection check the chassis to grid with a voltmeter. I goofed once and thought I was a the grid (which was near 0v) but was in fact at a B+ take off (the video test point was next to a B+ test point, it was late and I was tired). You dont want to fry your DVD or video source. to be safe you could isolate with a large value cap like a 1uf or larger. Too small and you will get....smear  but you dont really need it, just check that voltage before hooking up. I do this all the time to see how well my IF alignment went. If its as good as the composite signal then I know it cant get any better. Last edited by DaveWM; 05-23-2010 at 09:48 PM.
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#5
05-23-2010, 09:49 PM
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oh one more thing I guess its possible that the video signal will be out of phase, I have heard this can happen but I have not seen it. I know this work on at least a few of the different brand of tv's I have tried it on.
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