Does anyone know if the Playchoice 10 uses the same pallete as the NES? I beleive that it does, but I have heard some people say it doesn't. Do any of the VS Unisystem carts have a PPU with the same pallete as the NES? I am looking to do a mod for my NES to get RGB output, and possibly to mod a PlayChoice 10 to work on an NTSC TV set.
The PlayChoice-10 does use the same palette, mostly - it is missing the grays at $1D/$2D/$3D, and color emphasis works completely differently, forcing each channel to maximum intensity (which can cause problems in some games which set all 3 bits, expecting to dim the screen by 25% but instead resulting in a solid white screen).
I have also discovered that the PlayChoice 10 will ouput in a special inverted RGB instead of a standard RGB. So, what sorts of games would be affected by this slight pallete change? And what games would be messed up with the color emphasis? Just some examples would be nice. I am looking to RGB mod my NES, or possibly to NTSC mod a Playchoice 10 arcade board. I am guessing only very new games will be having problems, but you said some grey colors are missing? Would this make most NES games look very strange, or only a few? Thanks for the help.
Edit: I have been doing some investigating and I have come to the conclusion that most NES games will work just fine even with the differences, except that some homebrew carts that take advantage of color emphasis features will be the ones that look odd. Most NES games don't actually use thes features, am I correct? Of course, if I did this mod I would be keeping my normal NTSC NES intact, I will actually be modding a Famicom, because this RGB mod will be going into a handheld system!
For your information, the inverted colors are a result of the amplifier on the board, not the PPU itself. This PPU will work in the NES without inverted colors, but a lot of colors look wrong because of the fact that the RGB PPU sort of "emulates" the composite PPU with preset values on a 512-color chip. They didn't select a lot of these values very well, usually resulting in bright, saturated colors and even a few duplicates (that shouldn't be duplicated).
However, I figured out how to build an amplifier that'll fix most of the problems. First, connect a 3.3K resistor between the red & green pins (14 & 15), green & blue (15 & 16), and red and blue (14 & 16). Then run each of these signals into the base of a 2SA933 (NTE17) or 2SA937 (NTE290A) transistor. Ground the collectors and run the emitters out to the base of another transistor of the same type (and to a 10K pullup resistor connected to the +5V supply). Ground those transistors' collectors, and run the emitters to 330uF caps (neg. end) and to 150-ohm pullup resistors (to +5V). Connect the + end of the caps to your monitor. The sync signal is on the same pin as the composite signal of the NES PPU, and the NES (or Famicom)'s video amp should sufficiently amplify the sync signal (on the top-loader NES, replace the 510-ohm resistor with a 300-390-ohm resistor, remove the other 2 resistors connected to the video amp transistor, and use a 110-120-ohm resistor in series with 1 330uF cap).
If anyone knows how to post a photo to these messages, I can include a schematic.
rt9342 wrote:
If anyone knows how to post a photo to these messages, I can include a schematic.
Register on
Quietust's NESdevWiki and then
upload it there.
IIrc, using a Duck Hunt Vs. PPU is the same. I think Vs. Tennis is the other one. It seems a little less shameful hurting one of those boards than a kickass PC10 board.
One thing I've always been quite curious about is whether you can put the NES PPU back on the PC10 or VS. board to make it wok so you dont have to throw the damn thing out. That's what's always put me off from the mod...having a dead arcade board that's unfixable.
-Rob
I agree - get a Duck Hunt PPU (or same type) if possible. I recommend trying to find an RP2C03C, as opposed to the RC2C03B that usually comes with dual-monitor Playchoice boards. The "RC" version appears to have distortion in the last column of pixels, apparently sprite-related (at least mine does). Also I had some problems with the "RC" version in the top-loader NES, which I fixed by adding a pullup resistor. But if you're planning to build your own video amp, and want to try my design (by the way, I stated to use 330uF caps - 220uF is what I meant, though 330uF should also work) , a junk Playchoice board will have plenty of 2SA933 transistors.
Oh, and I never tried putting a composite PPU in a Playchoice board - I figured it would work and I've heard that it does, except that the picture is monochrome, but apparently it's only because it's missing the green trimmer cap that you see on the NES board. You could probably remove this cap from your NES if using an RGB PPU and install it on the Playchoice board. You may have to rewire the sync amp, though - if you run pin 21 to the base of a 2SA933 transistor, ground the collector, and connect the emitter to a 300-390-ohm pullup resistor (to +5V) and to the negative end of a 220uF cap.....then connect the other end of the cap to a 110-120-ohm resistor - you should get a clean composite signal from the other end of the resistor.
rt9342: interesting.
You should post that info on the wiki.
We're eventually going to be documenting all the intricacies/differences of the digital versus analog/composite ppus there, so this RC versus RP stuff definitely belongs.
Lord Nightmare