Core Grafx bad composite output

[Ergot_Cholera]

This is what I get from the din socket and also via my AV Booster.
 I have tested it with a Tennokoe 2 that I have RGB modded that uses pure sync and I get a perfect image.

[thesteve]

no luma
possible modded unit (svid)

[Ergot_Cholera]

It isn't modified. What is the cause of the lack of luma signal?

[thesteve]

well it should be coming off pin40 of the 6260 into a resistor ladder where it mixes with the other parts of the video sig

[Ergot_Cholera]

I already tried to trace it from the C6260, but I got lost through all the resistors and (transistors?). I will try tracing it from the other end. Nothing looks obviously damaged (but then it probably never does).
If I can't find an obvious solution that is simple enough for my lack of knowledge to comprehend then I will just use pure sync with an RGB mod.