I know exactly what your problem is.
You have a defective convergence output IC. Your set has two of these and they should both be replaced.
If you are handy with electronics and can solder and unsolder electronic components, you might be able to fix this yourself. I can give you some pointers if you feel comfortable doing this.
If you decide to call a tech, give him the make and model number, tell him what you told me and that you suspect a convergence output IC failure. He should immediately know exactly what to do, what parts to bring, and be able to fix it in your home in a little over an hour. Cost should be in the $300 range, depending on where you live.
Good luck, let me know if you need anymore information regarding this issue, and thanks for using JustAnswer!
The board with these output IC's is a large board on the right side when viewed from the back. You'll see a large heat sink on the right edge of this board, this has the two output IC's mounted on it. The part number of the IC's is STK392-110. There will be two of them, and they should both be replaced. Replace them with STK392-150 or -180, they are the improved replacements. You can order them from MCM Electronics by that part number.
Once you find them, you'll need to get the board out of the set so that you can unsolder them. You need to unplug all of the connectors that go to this board. They will only go to the connectors they came from, since they are all different number of pins, so you can't mix them up except for the ones that go to the convergence yokes. But usually, the plugs have a painted color to correspond to the tube they go to, and that color is marked on the board (if you mix them up, it won't damage anything, you'll just get really bad convergence). You will also see some 1 watt resistors, and there will be 6 of these that are in the 1 to 4 ohm range, specifically RK42, RK46, RK50, RK54, RK58, and RK60. You'll need to check these for any that are open or obviously burned, and replace them. Let me know if you need part numbers for these.
You are going to need a small pencil soldering iron (in the 25 watt range), some electronics solder (not the same thing that plumbers use), some desoldering braid and some silicone heat sink compound. You can get all of this at any Radio Shack.
Take the soldering iron, and once it's hot, you must "tin" the tip with fresh solder. Put plenty of fresh solder on the tip, then shake off the excess Then, just carefully place the tip on a piece of desoldering braid and put that on one lead from a convergence output IC, feed a little fresh solder onto it, and the fresh solder and the solder on the IC pin will wick away by capillary action, leaving you with just the pin of the IC unsoldered from the pad it was soldered to. This is going to take some patience and practice, and you should use a magnifying glass or very strong reading glasses when you do this.
Once all the pins are unsoldered, you can remove the screws holding the IC to the heat sink and remove it. Take a new IC and spread a thin layer of heat sink compound on the back of it, then mount it on the heat sink. It will be tricky getting all the pins to go through the PC board without bending, but with patience, you'll get it.
Now "tin" the soldering iron tip with fresh solder again. Put plenty of fresh solder on the tip, then shake off the excess Then, just carefully place the tip on one lead from a convergence output IC, feed a little fresh solder onto it, then move to the next pin and repeat. After you've done 4 or 5 pins, take the iron away and re-tin the tip with plenty of fresh solder and shake off the excess. You may want to wipe the tip off with a rag before putting fresh solder on the tip.
Once you're done, carefully check your work to makes sure you didn't accidentally solder two adjacent pins together. If you did, just use the desoldering braid to suck up the solder, and reapply new solder.
Once you're happy with that, reassemble everything, cross your fingers, and see if it works!
Let me know how that sounds or if you need more advice.