EGA to PVM

I bought an EGA display card for ISA recently. EGA games run without scan doubling so they looked a bit different originally on real EGA monitor when compared to VGA monitor and I hadn't actually ever seen this so I figured I'd try. Unfortunately I don't have an EGA monitor or CGA monitor (low resolution EGA is compatible with CGA-monitors) and they are quite difficult to come by. EGA as well as CGA uses digital TTL signals instead of analog RGB like VGA monitors. VGA monitors are also incompatible with CGA and EGA timings so I would have to figure something out.

I do have a PVM capable of displaying NTSC signals (basically a TV), including RGB input and since most EGA games are running in the low resolution mode with NTSC compatible timing, I figured it might be relatively easy to botch something up. PVM only accepts CSYNC so I would have to convert VSYNC and HSYNC. Unfortunately they need to be inverted so I had to use an active logic circuit for that instead of just something passive. Luckily the logic is quite simple. Another thing is that TTL levels are too high for PVM, but simply placing 1 kohm resistor in series divides the voltage down sufficiently (into 75 ohm input). Maybe this division is even a bit too much, but it's what I had at hand. Below is the schematic I used.

Unfortunately the CGA/EGA color brown is handled in a "nonlinear" fashing and would require a bit more logic to display it correctly. Here it instead of being brown looks more yellow. However, the other 15 colors are fine.

This is how it would look with the correct shade of brown.

My botched board is maybe a bit nasty, but it works fine.