the video processor for the DVD is on a different board, usually either the DVD driver board, or the DVD signals on newer machines tends to go straight to the HDMI board and is run through some DACs to make the analog outputs. it could be as simple as the analog video amp being bad or the HDMI chip, or other video processor chip. if you're getting audio there's nothing wrong with the DVD mech or optics, since the video and audio reside in the same data stream from the disk surface. if it's a black screen but you have sync, then it's most likely somewhere other than the analog chip that buffers the signals. have you tried checking other video outputs for signal (if any)? in 480p or 480i mode, the green jack will give a visible (in black and white, and a double picture in 480p) on a composite monitor. if you have signal there, chances are it's the combiner for the composite signal, or an analog switch in the composite signal chain (like the switch that switches between VCR and DVD video, which it could be). a lot of these chips are surface mount dips that have very small pin pitches, or worse, little 24 pin BGA chips with the solder blobs UNDER the chip. these aren't simple to replace anymore (even with SMT skills, the BGA chips are pretty much a no-go, since you have to place the chip "blind", and if it works it works, but if it doesn't work you're done...)