Sanyo 31C426 RGB input pinout

[ituba]

Thanks Titan1a, dr.ido, Zenith26kc20, and Findm-Keepm for your help.

I could not find any info on old Proton TVs, but I think Findm-Keepm has the correct answer and it is a digital RGB input. I pulled the rear cover and took pictures of the circuit board the RGB input is connected to. My understanding of electronics is limited, but it seems to me that the RGB input connects to the two ICs on the front of the board, and these appear to be digital gates.

So, Titan1a, this would work well with your Commodore 128.