Sylvania 1-076 arrived!

[jeyurkon]

Originally Posted by John Marinello

Why would you have to shim the yoke? Can't you slide it up snug against the bell of the CRT?
Your picture is really looking good!

The yoke sits in a half tube that has a slot. A thumbscrew goes through the slot to allow you to rotate the yoke. The nut that the thumbscrew goes into can slide along the length of the yoke. Once in position you're supposed to tighten the thumbscrew. If you don't it doesn't stay in position. The problem is that when I tighten the thumbscrew the front of the yoke is too low and the rear is just a tad too high.



The half tube in the early sets had slots to allow you to adjust it's position. In later production they just spot welded it into place. I guess the replacement yoke doesn't match the physical shape of the original yokes well enough. The slots are still there. I could drill out the spot welds and add the adjustment, but I rather just shim the yoke between it and the half tube.


John

[jeyurkon]

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