480z system disk on ebayu

Not really RGB... There's a colour lookup table (a couple of TTL RAMs) on the hi-res board. It outputs an 8 bit value depending on its contents and the contents of the video memory for the current pixel. The output of that lookup table goes to 2 places. The first is an 8 bit DAC on the hi-res board. That's used for the monochrome greyscale output. The other is to the 26 pin connector. To that you can connect the RGB output board or a PAL encoder (which I have never seen). The RGB output board, which is mounted on the bracket for the BNC connectors, is 3 simple DACs (3 bits each for R and G, 2 bits for B) and a circuit to produce sync-on-green if you need it. No. If the hi-res board works without the RGB board, then the problem is on the latter. -tony