I need to find the pincushion circuit on my RCA F32632SB TV to check a problem with the TV displaying an hour glass picture. Where can I find a picture of this or a manual to guide me to the circuit?
The pincushion it intimately related to the horizontal circuits,the electron beam must travel farther to reach the corners of the crt and it does to the middle and so without pincushion circuits the raster would be bowed in on the sides on crts 27 inches are larger.Pincushion corrections straightens the raster by modulating the horizontal yoke current at a vertical rate.In an RCA tv the pincushion circuits are usually numbered 4800and the pin amp will probably be numbered 4801,its drive transistor should be Q4802,R4802 will be the width control,and R4805 the e/w pin amplitude. its inputs from the vertical should be Q4801 (subtractor) Q4803 (buffer) you should have a parabola waveform at 4801,yoke current can be modulated here without effecting high voltage.when Q4802 conducts voltage should decrease across Q4801 and the voltage drop across the yoke increases. The east west pin amp control 4805 controls how much of the vertical parabola is input to U4801 to compensate for changes in width caused by variations in beam current.By varying the e/w control resistor you can know if the circuit fault is in the input or output,if the picture varies in size the fault is in the input to U4801,if it does not vary check the output or U4801......hope that helps
Jan 15, 2009 |
RCA F32632SB 32" TV