I have a little DSO Nano, it's kind of crap though throwing it on there I get this:
I have a few Capcom ZN2 PCBs which use nearly identical main boards and with the same view on the scope I get this:
it seems to be pulsing correctly but it's not getting pulled up between pulses.
I tried to follow the sync traces and quickly discovered that on my G-net the sync line reads continuity to ground (this doesn't happen on my ZN2).
I did manage to follow the trances it goes from the JAMMA edge to the video header and then through a filter array (FL531 by the video header), before going to pin 14 of an SMD 74F244 (IC355 under near the ROM board connector). Other than the filter array there doesn't appear to be any resistors, caps or any other components between the output pins and this chip.
The video ground is the pin adjacent to sync on the filter array, so it's possible it's shorted internally but it also looks like a BGA mounted component and unbelievably tiny, I don't even know how I'd go about replacing it with my equipment. The 74F244 would be easier to replace but it's located directly under the ROM board so it'd be difficult to test while running, unless I soldered some wires to it or something.
I suppose I could remove the 74F244 and see if the short still exists as that would rule out the filter and I wouldn't have to bother with trying to remove it. I'm open to suggestions.
