Tuesday, February 26, 2008

Non-inverted video from the PC10

The PC10s PPU, the 2C03B, outputs regular RGB. It is inverted on-board en-route to the monitor.

Since my monitor is on it's last legs, and old Nintendo monitors are selling for as much as a new one from Happ, I'd really like to get regular non-inverted video straight from the board. Inverting it twice is hardly ideal, and surely some signal is lost.

I'm eyeballing the PCH1-CPU Schematic sheet 4 and there's some crazy crap going on, like everything Nintendo did back then this looks a little bit over engineered.

I get out of my depth pretty quick when it comes to looking at a drawing of some op-amps, capacitors, and transistors, and figuring out "what it does", but I think I can tap one of the legs of each 'gain' pot with a small resistor 50-100 ohms and have a usable signal. If all else fails, I can tap the unamplified RGB signals, and build my own amp, following the instructions of folks who've mounted the PPU into a regular old NES.

Also, I think I need to tap the NES's reset line on the PC10 board, to get some games to work properly. I'm thinking that the bus is not initialized the same way it is on a real NES, and on-cart RAM's suffer as a result. Being able to "start" the NES, then reset it, may be the key to all that.

I have a little perfboard leftover, so tonight I'll figure out how I'll mount it, and which signals I want to bring off of the PC10's board. I'll have two NES controller ports, non-inverted RGB video, and reset line. That's 15 pins so far, sounds like a mess in the making.

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