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Old 09-02-2018, 05:50 PM
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It's hard to trace through where the grid bias of the video amp comes from, but a good thing to try first might be to open the connections to the detectors by disconecting L20 and L28, then tie L20 and L28 together as a video injection point. This should work OK for chroma, as it is capacitively coupled, but you may have to supply some negative grid bias for the video amp (schematic says -.8 v at the grid). But that is after the delay line, so just try coupling video through and see what happens first. Or, measure the DC at the detector output before you modify anything, to get an idea of what's needed.
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