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There is an apparatus on the back of your picture tube called a yoke.This distributes your picture on your pic tube uniformly.If this or the circuits enabling it malfunction,then you will get distortion-namely an hour glass shape.Tv has to be trouble shooted.
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
I looked up this model and found the following electolytic capacitors to be the most likely culprits within the pincushion circuit. Check these first. The starred one is the one I have replaced in the past to resolve this.
Sorry Ginko, but a convergence problem would have the curves down from the top and up from the bottom. The hourglass shape is a pincushion problem. This can be as simple as a bad capacitor in the pincushion circuit.
Could you please confirm the model number so I can look up the probable part?
I am sorry that its took so long for me to reply been backed up in shop, anyway what you have is bad solder joints on large Diodes Resolder ends on all of them and this should slove your problem if you havent done so by now.
picture is starting to curve in from the sides like the shape of an hour glass.
Is the tube shot?
is it something less costly?
YOUR PROBLEM is in pincushion correction circuit.call skilled tech to fix it.
it will not take much time.