|
Jerry:
The primary cause of retrace lines in that TV is the absence of a blanking circuit. The CRT control grid returns directly to ground. It needs a 25 to 35 volt negative pulse to cut off the CRT during vertical retrace. When everything in that TV is working, there is little to spare so there's no place to get the negative vertical pulse without upsetting something else. The vertical output plate goes positive, the cathode is grounded, the B+ feed has nothing to spare so it leaves the oscillator plate. That's 60 v p/p, but at very high impedance so bleeding some off for blanking will reduce the vertical size and upset the oscillator timing. Look over some other GE portable designs of the era and you will see blanking schemes that could not be used on the 9" TV. I suspect the blanking circuit was the subject of a few engineering meetings with product planning. Finance eventually won out. It was a cost compromise and justified as a differentiator and a reason to step the customer up to the 14". That TV eventually cost GE a bundle. It sold for $99 and was quietly recalled to replace every 9QP4 CRT. Off-on-volume controls were another recurring problem.
It would require a design effort using a transistor or two to isolate the CRT blanking network from the other circuitry. The chassis design and PC layout leave little heat-free room for additional components. In short, it is expected to have retrace lines as designed.
Don
|