I don't know enough about these boards to suggest how to proceed exactly. Since the sync signal appears to be good I would start by checking the RGB output lines and working back from there. It may be that there is some incorrect colour information being sent outside the display area that is causing the monitor to set a false reference for the black level. This could cause a screen image like the one you are experiencing.

Before moving to the next step, I would possibly first want to be sure it's really not some cold solder joint on the cpu, and check continuity between cpu legs and further points on the pcb. Then check if coin input shows an output on the Jamma edge to the coin counter, to see if the game might be actually running. If yes, check audio and video circuits, if no, ehm, memory? This is more of a wild guess.. Curious to see where this ends up!

I would check video ram next. Also could check the rgb signals on jamma side.

Try checking the output to the coin counter to see if it responds to the coin input

OK - so the video output circuitry is ok - demonstrated by the sync signal. The CPU functionality seems pretty good, demonstrated by all of the activity, even if not verified by comparing the running code to a logic analyzer just yet. So that would mean either there is not the correct information being placed in memory, or it cannot be retrieved properly from the memory. So that puts us into the addressing circuitry OR the actual memory. Unlikely to be a memory chip issue if is shows nothing but a blank screen, maybe more likely an addressing issue?

Based on all of the checks that have passed thus far, and having watched all the other double dragon repairs you've done, I'd have a look at the rams and surrounding support circuitry. Knocked out all of the easy checks, so grab the SCUBA mask, time to go deeper. :) Love this idea, by the way.

You checked some of the roms (or maybe all), but did you also check the prom (ic101)? Looking at the video part of the schematic this seems essential for video output. Not sure if there is something wrong with the video, but an all white screen seems kinda odd. I would check the signals in the video circuitry to see if the inputs are doing anything. On page 5/9 of the schematic you can see the input signals in the bottom left corner, can you take a look if there is any activity there? Also looks like this game has no watchdog, so it might just be stuck due to a ram issue, or an addressing issue. So might be worth checking the buffers of the address and data lines.

The no sound thing seems weird if the game is running to some degree. I would check the sound cpu next. Great video, like the interactive help bit 😉

Checke, Check mit Fluke den Bus und die RAMs. Falls ok, die DACs checken.

Dead Fajitsu maybe

Is it possible to exchange the top/bottom Boards with working ones (see repair phoenix)? The cpu is working; but is there activity on the eprom and ram chips?

VSync of 57Hz is a little low. Should be closer 60Hz and might be why the screen is rolling if your bench monitor doesn't handle the variation as well as a real monitor. Might want to start looking at the Sync Chain a bit more with the scope (IC128 and back from that). I would look at the RGB to see if there is any activity on those, and then follow it back to IC83 and IC100. Even if the CPU was dead, you should still get something on the screen even if it's a solid color screen. The screen should be stable too.

Clean PCB wat NOT step 1 !!!!

mouse pee! destruction