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.
If you want your own version of this adapter, you can download the KiCad source files and gerbers for production here or order the gerbers directly from PCBWay, which helps me out with some credit for manufacturing future PCBs.