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Yokes
I read in an RCA TV servicing guide that the trapezoidal raster that I had would be caused by a problem with the vertical portion of the yoke. I don't understand that, I really thought it would be the horizontal, but decided to check it out.
In order to ring test the sections properly I have to remove the core. I started to do that, but after removing the damping resistors for the vertical windings I decided to check them. They are supposed to be 560 ohms each. They are 680 ohms and 725 ohms. I think that's enough to cause a problem and I should have checked that before swapping the yokes.
I'm trying to decide whether to replace the resistors and reassemble the yoke, or to continue the testing. I'd have to unwind a lot of iron wire and rewind it carefully later. To check the coils individually it's necessary to reduce the mutual inductance by removing the core. However, the vertical and horizontal shouldn't have much coupling. I ring tested both and got 9 rings each. There might not be a short and the real problem could have been due to the bad damping resistors.
In either case, I'm not going to put it back in this set since Sylvania says that this model yoke shouldn't be used with the horizontal choke that is in the set because of danger of breakdown.
John
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