| Electronics > Repair |
| Fix vertical hold on a monochrome monitor |
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| wasedadoc:
The pot adjusts the free running frequency of the oscillator to be slightly slower than the frame rate of the video signal. The vertical sync pulse "kicks" the oscillator to complete its cycle and start a new one slightly sooner than it would without the kick. In other words the period of the oscillator becomes exactly the same as the time between vertical sync pulses. There is typically at least a few percent leeway on how slow the free running frequency can be before the kick fails to be effective. It is not uncommon to see the picture height change slightly within the lock range. |
| rippenburn:
Thank you! I have been asking this question all over the Internet in relation to the Doppler effect on signals broadcast from the Apollo spacecraft. NASA used back-to-back VTRs to compensate for the effect. But I can't see that travelling at 3,000 mph would have much effect on the timing of the frames when EM travels at the speed of light. I calculated it would be around +/- 0.024% difference, which I would have thought was within the range of the vertical hold on a TV. So why not just stabilize the incoming picture and rebroadcast it with a TV camera, like the old Kinescope? |
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