IC is intergrated Circuit. Cost close to $100. in parts for the two IC's. There appear to be some cheap copies that have given results that range from OK to virtually 100% failure. It is highly recommended to buy parts that are known to be original Sanyo chips.
Convergence circuits correct the size, shape, and position of the scanned image (raster) by applying voltages and waveforms to the secondary (sub) deflection yokes on the neck of each CRT. These are windings in which a change in current results in a magnetic field that affects the behavior of the electron beam that scans the image on the phosphor. These yokes have horizontal and vertical windings similar to deflection yokes, but carry much less current and much lower voltages. Still, controlling the beam with the precision needed to match the images in all three tubes requires a reasonable amount of power. The amplifiers that drive these yokes are similar to those used in less expensive audio applications such as lower end receivers and portable (boom box) devices.
There are six channels that need to be amplified, horizontal and vertical for red, green, and blue. Most systems use integrated circuit designs with 2, 3, or 6 channels per chip. They are almost always STK series chips made by Sanyo. Some sets have used discrete transistors for these amps, but they are relatively rare. Most of the chips range in power rating from 20 watts to 70 watts. The run constantly when the set is on so they do tend to get hot. Temperatures in the range of 130 to 160 degrees F are not uncommon. Imagine an audio receiver running with the volume at a fairly loud level constantly. This is what these units do. Consequently, there are failures.
The correction starts with a series of waveforms applied to the amplifiers, along with a small dc offset. The waveforms are typically combinations of parabolas (for correction such as pincushion), sawtooths or ramp functions (for keystone and skew), and more complex patterns for point convergence. Vertical correction is applied at horizontal scan rates or factors and multiples of it, and horizontal correction is applied at vertical rates or factors and multiples of it. The chips must, therefore operate over frequencies that are typical of audio amps for conventional NTSC systems, and much higher rates for HD systems. The bandwidth of the ICs ranges from just adequate for NTSC as roughly 15kHz to over 100kHz, far beyond what is needed for HD applications. Most of the current chips have adequate bandwidth, some from a few years ago are marginal and should be upgraded to later versions. I will cover that in another post.
The dc offset is typically no more than a few hundred millivolts. Too much dc, or too much correction at the limits of the capability of the chips can cause them to run very hot. Heat is not a good thing for most semiconductors, so proper set-up is important. The dc offset is typically going to effect position changes (called static convergence) with little or no effect on the size and shape of the picture (called dynamic convergence).
The waveforms are generally generated in a circuit area called the convergence generator, which may be a separate module or combined with another set of circuits on a larger board. The correction signals are then applied to the input to the output ICs as a combination of the waveforms needed to correct the image. At that point the signals are in the hundreds of millivolts to perhaps a couple of volts. The output ICs amplify them and provide the power to drive the convergence yokes. They are usually powered by + and - supplies ranging from about 16 volts to 40 volts, depending on the design of the set and the chips chosen for that application.
