Strange Naomi video problem

[Ace`]

I've got a Naomi 1 motherboard on the bench that runs as I have audio but doesn't output video, I've tried swapping the 315-6145 dac with a few from junk boards thinking that would be it, as it seems to be a fairly common failure. After that didn't work I did some tracing and found some shorted diodes connected to the rgb and sync lines, after replacing these I get h/v sync at the vga port but the rgb lines are low, too low for my monitor to accept (about 0.8v).

Looking at the dreamcast schematics the circuit looks the same and I've also ruled out the three caps connected to rgb lines and the three 75ohm resistors, I've also tried a different known working filter board which made no difference.

It's possible this was a F355 board originally as it's an early one I was thinking maybe the video output was never used and I am missing some factory bodge wires?

I found this image used for the hdmi instructions and noticed some bodge wires which mine doesn't have, but I am clutching at straws now. Anyone seen this issue before?

 

[Ace`]

I've made some progress, the vsync pulse is there but it's not right after comparing it to a working board on the oscope. I got a very poor image when wiring it up to a 15khz arcade monitor which of course doesn't sync but at least I can see it's working and passes all ram tests so just this one fault left to figure out.

 

[Ace`]

Finally figured this out after tracing out both sync lines I eventually came to two tiny 6hm resistors on the bottom of the board one for each sync, one was fine but the other read 2.6k ohms. I took a replacement from a junk board and it is now 100%. Looks like when the diode shorted it cooked the resistor too, although there was no visible damage.