NotTaR of Television Sets : Comments on vertical problems           
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Comments on vertical problems

(From: Bert Christensen (bert.christensen@rose.com).)

As a general rule, vertical faults can be divided into two types: ones that cause geometric distortion (a circle will not be round) and those that simply black out a portion of the screen. The former are faults in the vertical oscillator, drive, or output stages. The latter are blanking faults. Blanking faults are almost always caused by electrolytic capacitors changing value and thereby changing the timing of the pulses which blank the screen during vertical retrace. In other words, the pulses are turning off the video signals at the wrong time.

The most common true vertical fault is geometric distortion and a foldover of white lines at the top of the screen. This is almost always caused by the electrolytic capacitor on or near the collector of the vertical output transistor or part of the IC which has the supply voltage (B+) on it. In the old tube days, the general rule was that bottom distortion was in the cathode of the output tube and distortion at the top was caused by a fault in the drive circuit.