I already worked out why…and I very much doubt many of the cmvs consoles people build are set up to output video correctly. if you have one, get out a multimeter and check the voltage on the RGBS lines. Not surprised some out there are blowing up OSSC and gwscart units when they’re giving them 5 times the current they should be
I covered it in my CMVS build thread here: I'm building a NeoGeo CMVS! Progress and Details! (Round 2!), specifically this post: I'm building a NeoGeo CMVS! Progress and Details! (Round 2!)
you’re getting 5v output on those lines unless you knock them down properly:
Last week I did complete my RGB circuit and installed it into the CMVS I built. It knocks each RGB line down to the correct pre-amp voltage using some resistors, and then they’re put through to a THS7316 amp which outputs them at the correct 0.7v 75ohm for each line.
you dont want to feed 5v to the ossc on anything other than the scart blanking pin…
also, the above is exactly how the AES deals with the video. it’s generated by the ppu, knocked down to a pre-amp voltage then put through an amp before going to the output.