COMTECH FRAME LOCKING PROBLEM CURE
Lots of people have asked me to send info on how to cure this problem
Which is that when large white area's of the pictures suddenly happens such as the sky or bench lamp the frame rolls.
The cause is LF distortion in the Video output stage NE592 because the video input bias to the amp gets to the other input because the decoupling cap does not work on low frequencies.
Bias the other input on it's own and you will see a big difference both Visual and on an Oscilloscope
Don't try increasing the cap just do the above (otherwise other problems arise).
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Note you loose your guarantee !
To do this remove the 10K SM resistor going from pins 1 and 8
add a 10K resistor (not SM) between pins 1 (input) and 3 (-0V)
add a 10K resistor (not SM) between pins 1 (input) and 6 (+ supply)
The real video goes in on pin 8 and has its own biasing parts.
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Or for better gain control change the above 10K pot to a 1K and set to about half way. If you set it to full gain you will have no Colour !