#31
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Yep, ringing in the horizontal yoke. Check the 56pF cap or 1K resistor hidden in the yoke.
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#32
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To avoid a possible wild goose chase, it might be worthwhile to ascertain that the bars are deflection-based, and not in the video chain. Shunt the CRT control grid to ground with a cap, which kills the video. If the bars are unaffected, they are in the deflection system. Cap value not critical, anywhere from .047 - .1 or so.
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#33
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What! You mean you didn't wipe all that crusty old wax off so they look like shinny NOS? How dare you.
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#34
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Quote:
Quote:
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John |
#35
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I don't think so. The centering control works by adjusting a DC bias current through the horizontal yoke winding. Check the voltage across the centering control and see if the voltage on the wiper changes as you adjust it.
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Audiokarma |
#36
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Progress report. The horizontal centering control is broken. It stops at around 10ohm and it's supposed to be a 20 ohm control. Does anyone have a 20ohm control w/center tap and a short thumb screw shaft?
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John |
#37
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Might be able to jump a 20 Ohm across it's terminals for a temp patch.
__________________
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 |
#38
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Regarding the horizontal ringing, after shunting the crt control grid to ground to confirm the issue was not in the video, I replaced the 56pf capacitor in the yoke and while the black bars didn't completely disappear, they seemed to be less noticeable. Is it possible the cause can be coming from more than one place?
I also replaced the 6SN7 in the vertical oscillator and the vertical collapse didn't return after that. I'm going to keep an eye on it though as it went away and returned before.
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John |
#39
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stuff can work together to make horizontal ringing.
__________________
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 |
#40
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Quote:
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Audiokarma |
#41
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Progress! I found that the problem with the horizontal centering was not due to a bad control pot. The issue was with a two section capacitor that I mistook for a single section. I had been shorting out C207 to C208 which shorted the upper half of the wiper. I rebuilt the capacitor again with both 100uf caps in place and the horizontal centering now works as expected. This repair also allowed me to adjust the focus coil for its intended purpose of uniform focus instead of adjusting it to center the raster. Now I have a centered, fairly well focused image .
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John |
#42
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I'm going to swap the original 10FP4 back into the set (if you'll remember it was brighter and had more contrast, but didn't focus as well) to see how that one looks now that I can move the focus coil more freely. I also need to find vintage replacement 56pf and 82pf capacitors. I have modern replacements in the set in these values and they will need to be swapped out. Anyone have good, but old, replacements for those caps? I also would like to see if adding a vertical retrace blanking circuit is feesable for this set. I have read about this modification, but only on sets where the video is fed to the cathode, not to the grid like this set is. Does anyone know if you can do a retrace blanking mod on sets with video fed to the grid?
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John |
#43
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Making slow progress. I'm pretty much down to one remaining problem. There are diagonal lines in the video that I suspect are caused by my video circuit. Phil is also working on a video inverter circuit for his set, but didn't mention the same issue, perhaps it's unique to my set. The lines are more noticeable on brighter scenes and are extremely difficult to film. Luckily while watching Daniel Tiger with my daughter this morning I found the perfect scene to show the problem. See video here https://youtu.be/QpJ0pEOIjN8. Anyone have any thoughts?
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John |
#44
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Those look like artifacts of the color sub carrier. Your best bet would be to not drive it with the yellow composite video output of your source, but instead use the green component output or the monochrome half of the S-video output...That will give you video free from color sub carrier.
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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 |
#45
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Quote:
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John |
Audiokarma |
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