Drakon
Active Member
As I'm sure a lot of people on this forum already know the nes/famicom outputs a nice looking composite video signal at best from the stock system. I got a bit tired of using this blurry mess of a video signal so I searched around the internet for information on how to remedy this annoying issue. Luckily there is a fix! However....this requires you to buy a kinda hard to find and not always so cheap arcade board...... So the first thing you need is a playchoice pcb that has a working ppu (picture processing unit chippy...... thingy)
Here's the board (this is the dual moniter version but I'd assume a single moniter one would work too)
And more importantly, here's the chip you'll be needing
I've read that you can also use the ppu chips from a vs tennis or vs duck hunt chipset but they may be a different revision of the ppu and I also heard that the different revision has garbled graphics on one side of the screen.
The mod is a good chunk of work. You need to remove the original ppu chip from the nes pcb and attach your rgb ppu. The pin 14 15 and 16 of the ppu are the red green blue jets so keep them disconnected from the pcb. I also disconnect pin 17 because it seems to be a seperate ground for video. I soldered the ppu connections to a 40 pin ic connector on a piece of breadboard so here's how it looked after it was all wired up
Then I added some glue and built a cartridge slot that works much better
The video signal out of the ppu is unamped so you have to build yourself an amp. I designed an amp that brightens the signal perfectly by combining a few different amp designs that I found on the internet. Since I'm using s-video I just amped the brightness wire and left the colour at the original saturation. The colour is a tiny bit weak but still looks fantastic on my tv. Of course you could always amp the rgb wires but I figured that it makes more sense to make just one amp instead of 3 and I was fine with how the picture looks. Also I have to add a capacitor to my sync line for my picture to display right on my s-video encoder. I used a 220 uf 10v cap with the negative leg pointing towards the encoder board but I found that any cap works for some reason. Also a lm1881 sync seperator chip fixes the sync and removes the need for using the cap. But the cap was far cheaper.
You also have to be careful with how you wire up the grounds of your amp and the video circuit and you even have to be careful with how you wire the ground for the sound from the system otherwise you can end up with a picture like this
I found that using pin 20 of the ppu as video ground really cleans up the image.
So here's the difference between composite video from a stock nes and s-video from my nes
Pretty big results. The playchoice is a massive system and wiring it up for my supergun would be a mega pain since I've read that it outputs inverted colours. And if you build a socket for your ppu you can always stick the ppu back into the playchoice pcb if you ever want to use that again. On the playchoice pcb the ppu is socketed so you can easily remove it and put it back. The rgb ppu doesn't have 100% the same colour pallette as the regular nes. I heard it makes a very very small collection of games unplayable. Any lists of unplayable games I could find were all games that aren't popular at all. From playing games on my system I'd say the pallette is about 97% the same as a regular nes. And the few spots where the colours are different don't ruin the experience at all. This is probably the best use for a playchoice pcb and an old nes that I could find. This mod also will work on a famicom.
Here's the board (this is the dual moniter version but I'd assume a single moniter one would work too)
And more importantly, here's the chip you'll be needing
I've read that you can also use the ppu chips from a vs tennis or vs duck hunt chipset but they may be a different revision of the ppu and I also heard that the different revision has garbled graphics on one side of the screen.
The mod is a good chunk of work. You need to remove the original ppu chip from the nes pcb and attach your rgb ppu. The pin 14 15 and 16 of the ppu are the red green blue jets so keep them disconnected from the pcb. I also disconnect pin 17 because it seems to be a seperate ground for video. I soldered the ppu connections to a 40 pin ic connector on a piece of breadboard so here's how it looked after it was all wired up
Then I added some glue and built a cartridge slot that works much better
The video signal out of the ppu is unamped so you have to build yourself an amp. I designed an amp that brightens the signal perfectly by combining a few different amp designs that I found on the internet. Since I'm using s-video I just amped the brightness wire and left the colour at the original saturation. The colour is a tiny bit weak but still looks fantastic on my tv. Of course you could always amp the rgb wires but I figured that it makes more sense to make just one amp instead of 3 and I was fine with how the picture looks. Also I have to add a capacitor to my sync line for my picture to display right on my s-video encoder. I used a 220 uf 10v cap with the negative leg pointing towards the encoder board but I found that any cap works for some reason. Also a lm1881 sync seperator chip fixes the sync and removes the need for using the cap. But the cap was far cheaper.
You also have to be careful with how you wire up the grounds of your amp and the video circuit and you even have to be careful with how you wire the ground for the sound from the system otherwise you can end up with a picture like this
I found that using pin 20 of the ppu as video ground really cleans up the image.
So here's the difference between composite video from a stock nes and s-video from my nes
Pretty big results. The playchoice is a massive system and wiring it up for my supergun would be a mega pain since I've read that it outputs inverted colours. And if you build a socket for your ppu you can always stick the ppu back into the playchoice pcb if you ever want to use that again. On the playchoice pcb the ppu is socketed so you can easily remove it and put it back. The rgb ppu doesn't have 100% the same colour pallette as the regular nes. I heard it makes a very very small collection of games unplayable. Any lists of unplayable games I could find were all games that aren't popular at all. From playing games on my system I'd say the pallette is about 97% the same as a regular nes. And the few spots where the colours are different don't ruin the experience at all. This is probably the best use for a playchoice pcb and an old nes that I could find. This mod also will work on a famicom.
