August 1977 RCA Colortrak

[vol.2]

Originally Posted by pac.attack76

Not sure how to set convergence really. I've only ever done it on projection sets. Im guessing this is an in-line tube and I see what looks like 4 rings and a thumb wheel. Not sure what to do first.

Explanation of the ring below, but first, I think you should check the yoke for slippage. Looking closely at your screenshots, I think the yoke probably slipped, and it's pointing up too much. You can see in your grid that the image gets bigger towards the top. I think it would be fixed if you pointed the yoke down and glued it in place. You can imagine the effect of moving the position of the yoke in the same way that pointing a projector at screen distorts the image if it's pointing up or down (or left or right). It's going to bow the image outward in the direction that the lens is pointed.

It can be very dangerous to move a yoke when the set is on. Make sure you know how to be safe. Consider just doing it in small steps while it's turned off and then checking it. It will take longer, but you also probably don't have the correct safety equipment to do this while it's on.

The rings (maybe):

I've never done an RCA before, but rings can be for both purity and convergence.

Purity is the color uniformity across the entire screen that is effected by how far the yoke is pulled in or out from the base of the tube's neck.

If you can imagine, when you pull the yoke in and out in line with the neck, the whole image will get bigger and smaller. However, the relationship between the position of the yoke and the tube will effect the spot that the beams land on the inside face of the tube because you are changing the geometry of the beam landing when you adjust the yoke.

The purity rings basically allow you to dial in the beam landing by giving you some whole-screen adjustment for the purity. You generally adjust this by 1. setting the purity rings to dead center, 2. putting up the three color (R, G, B) stripe pattern on the screen, and then pulling the yoke in and out until the stripes are dead even, 3. putting up an all white image and adjusting the purity rings until the image is totally white on the sides.

The convergence can be set by rings, but it can also be set by a potentiometer. This is almost always found on a box attached to the flyback or tripler, or it's found on the neck board. I've personally never seen one anywhere else. When it's a potentiometer, it's just the horizontal convergence, and the remaining rings set the vertical.

So what I think your rings probably are is two for the purity and two for the vertical convergence, and there's probably a dial inside somewhere that does horizontal. But that's just a guess based on other sets I've done from the same time period. I've never worked on an RCA before, and sets in the 70s tended to be less similar in design than they became later on.

Again, I've never worked on an RCA before, but I would guess that the rear two of the four rings would be the vertical convergence, just from experience. The rings closest to the base of the neck are typically the purity rings, assuming it has them.

If you do end up messing with it, I would recommend picking up some thick electricians rubber gloves to move the rings. They are not foolproof, but they will at least keep you aware of your hands and what you are touching. I personally still use them. I also use an isolation transformer so that the TV is not directly connected to the power grid.