Hi! I am new to this forum. I just recently posted this same question at another forum, but that other forum seems to be more oriented towards program developers.
Here is the problem that I am having with my nesrgb console:
A few months ago I did the nesrgb mod on my PAL nes console. Back then the console was working perfectly fine with no issues whatsoever. It has been probably about 2 months since the las time I used it. Yesterday I played Probotector through my ossc for about 1 hour without any problems, but after an hour or so, I suddenly lost video and audio signals while the ossc displayed "no sync". I tried turning the console off and back on, but still nothing happened. I used 3 different scart cables but still couldn't get my ossc to recognize the signal coming out of my NES. (I am using high quality male to male scart cables since my consoles all have female scart plugs built in)
To make sure that the ossc was workong properly, I tested it with my PAL snes console by connecting it with the same scart cable that I used to connect the nesrgb console, and everything worked fine.
I then tested the voltages on different pins of the scart cable coming out of the nesgrb console to make sure that an actual signal was coming out of the console. The red, green and blue lines were all in the 0,6 volts range. Pins 8 and 16 (rgb switching) were in the 5v-6v range. The csync pin 20 had a 0,6 voltage as well.
I also opened up the console, inspected the board checked all the connections with a multimeter, and everything looked fine.
It looks like the ossc doesn't recognize the csync signal coming out of the console? Is there anything that I could do to fix this? I had soldered jumper j8 on the nesrgb board when I did the mod. I dont know if this has anything to do with the problem.
"CSync" for scart is a little misleading...its really CVBS 0.7v p-p
If you're getting voltage output on that I somehow doubt the NES is the culprit. You have too many variables going on here and you need to pair them down. Have you tried hooking up the system to a TV without an upscaler? They also sell $10 upscalers for VGA online...i would work down the chain to troubleshoot the console.