[Alex KL-1]

Originally Posted by Alex KL-1

Thanks! This makes sense, considering that some of these things have very simple and critical circuits (to reduce costs etc), not always optimized or routed.

I will play with grounding, routing and with sync separator too, in one particular 10" portable I'm restoring/modding that have horrific vertical interlace. Perhaps it will behaves a little better.

And perhaps will better for me to having only moderate expectations when injecting direct video of course.... hehe

I played with this Philco 10" set, first trying to add some shield for the vertical oscillator, since it is located just below the flyback transformer
This not helped much (but I don't removed it), so I decide to play with circuit.
After changing the grounding of vertical sync filter, from ground to +B (due to reference of oscillator input), and changing the input from sync separator from the original video output tap to a exclusive video buffer, then the vertical sync and interlace becomes very good; so good that the range of adjustment to sync become uncritical and I can easily adjust.
To be true, the major difference was when I changing the Vsync filter, so I presume that the ripple induced by the H switching was intruding into the oscillator, upsetting it.