After a respin of the PC88 colour video board, the PC8801mkII now has excellent digital colour video out.
Technically, I got the board revision done in time for RetroChallenge 2018, way back in September, but didn’t get this write-up done in time. Now, I have had a little more time to put this together. Apologies for the apparent lack of closure.
In the last update, the red and blue channels had been swapped, leading to incorrect colour. A hack-job of patch wiring fixed it, but there were some persistent green artifacts on the screen:
Swapping the channels over did in fact fix the colour problems, which just left the “ringing” green lines. Originally, I had chalked these up to electromagnetic interference, poor soldering, or a rookie error in board routing.
Luckily for me, I got p88sr (a PC88 emulator for the PC98) running, and noticed identical vertical green lines on the 98, which used nice, professionally-assembled, video cables for everything. Therefore, it must not have been my adapter.
I decided to mess with the monitor settings, and after setting the horizontal scale to a slightly different value, the lines went away. Hooray! I guess they must have been some kind of upscaler artifact.
Now I can enjoy Dragon Slayer.
I recently got a VGA2USB frame grabber, as well, and it shows some promise for grabbing PC88 and PC98 video. It just needs a little more tinkering, as it currently likes to cut off the bottom of the screen when presented with interlaced video.
With the new frame grabber, I hope to get some high-quality video captures of gameplay, since most of YouTube is shaky cam cell phone footage.