[lcaillo]

Not all problems with convergence are the output ICs. Most certainly are, but before changing parts, or even buying them, you want to be sure. There are some symptoms that are pretty good indicators, but some problems are not so obvious. I will try to describe some of the ways that, as a technician, I would determine whether or not the output ICs are defective.

Symptoms can vary. The most common and obvious would be when the convergence cannot be corrected in one color in one direction. This indicates that one channel of one of the chips is likely bad. It could also mean that you simply have a bad solder connection at the IC, the connection to the yokes, a resistor, or a connection coming from the convergence generator. The first thing to do in diagnosis is to observe the symptoms carefully. Try adjusting the red and blue horizontally and vertically if you have manual controls or in the service menu. Try running any auto convergence mode if you have it and watch each color. If one does not move in one direction you have a good indication that one channel is bad or where to look for a bad connection.

Intermittent problems with convergence may indicate simply bad connections at the ICs. Some problems that are not intermittent can be the same. Check the solder joints for ring cracks. Many times the factory does not deposit enough solder on the pins and repeated heating and cooling cycles can cause the solder to crack.

Some sets may not even power up. It is not uncommon for shorted convergence outputs to cause a shutdown of the set and/or to blow fuses. It is always a good idea to look for the obvious, such as blown fuses, burned resistors, bad solder connections, etc. A lot of the process of troubleshooting is observing things that simply don't fit with a normally operating system. Checking power supplies is always a good start. There are usually a number of different power supply lines at different voltages supplying various circuits. The convergence supplies are almost always a pair of + and - supplies. If one of them is not coming up or goes down faster than the other, you have an important clue. When one of the supplies is down, if the set does run, convergence will usually be bad on all three colors, and in both directions.

If you suspect that convergence outputs are bad and causing a shutdown condition, one way to be sure is to disconnect the supply lines to the chips. It is sometimes easier just to remove the chips altogether. Nearly all sets will run with no convergence outputs. You won't get any convergence correction and the pix will be curved in on all sides and offset, but you should be able to measure the + and - supplies at that point to be sure that they are present. While the chips are out, you can also measure the output resistors that sometimes open when a chip fails. I'll deal more with those in another post.

While the chips are out, it is a good idea to check the dc offset at the six inputs to the ICs from the convergence generator circuit. If it is more than a few hundred millivolts, you need to deal with that. It could be that the position control has been adjusted to its limit trying to correct convergence, but it could also mean a problem in the circuits that generate the correction voltages. Some auto convergence systems will try to correct for a bad chip and end up with severe conditions driving the inputs. This can be difficult to deal with, but usually is correctable by running the convergence process as soon as the circuit is repaired.