work in progress.

Hi Drakon.

ive been working on an rgb nes for a while now.

here is what ive done sofar.

I removed the ppu and installed a socket, removed 74ls373, replaced with socket and installed 74hc373 off of playchoice.

i also installed a 100pf cap between pin 24 and 20 on the ppu. powered it up and had music from Arkistas Ring. Ive read that its not really nessecary, but the playchoice does have this cap so i added it.

today i wired up the video amp and all of the wires that are going to go to the scart socket. i used the smallest sheilded mini-coax cable i had for rgbs, and the audio as well. i tapped the sync direct off of the ppu and i skipped the video amp with the video grounds. they go direct from pin 17 on the ppu through the sheilding to the scart socket. i have yet to wire and install the socket. thats really the only thing i have left besides finding a place to tap +5v and G off of for the amp power. my pcb is nes-cpu-11 if that helps.

after adding all this stuff today, i *Still* have music from Arkista's ring, and nothing went boom yet. its looking good.

I was going to install my Usb CNes in this as well, but with the sheilded cable ive got no real room to. ive decided to just build another deck for that instead.

the real test with this project though will be when i turn it on and see or not see any jailbars.

Ive seen your famicom kits you are using now with good results. i started building this before i knew about that.

one question. where can i tap 5v and amp ground from? whats the best spot?

also, i have no idea how to post pics of my work here.

You can tap 5v and ground from a million different places on the pcb. The kits I use take 5v and ground from the ppu 5v and ground pins. The simplest place to get 5v and ground from is the voltage regulator it only has 3 pins on it. Be careful that you grab 5v from the output pin of the regulator as the input pin is something like 12v. Anyway if you don't want to risk accidentally wiring up 12v you can get the power from either the ppu or the cpu pins. Here's a pinout of the ppu taken from moosmanns site:



Pin 40 is 5v, 20 is ground. The rgb chip shares the same pinout as the composite ppu except for rgb and sync. Also the playchoice comes with a 68 pf cap between pin 24 and ground not 100 pf.

To post a picture click the image that looks like a picture frame to the left of the link image that looks like a chain link

Also one thing I've noticed about the rgb from the ppu is that adding any length of wire between the rgb signals and your video encoder causes the quality to decrease. I forgot I had wires added to the rgb inputs that were about 3 inches long and that alone was enough for me to notice the picture being more blurry. That's why I use these kits they point blank range the rgb into the sony chip. After the rgb passes through the sony encoder the quality doesn't decrease. I have no idea about rgb tvs as I'm using s-video. But if the quality decreases going into the rgb video encoder I don't see why it wouldn't decrease going into a rgb tv.

Also when I wired up my nes-cpu-11 that was the original system I did it was such an ugly job and many many years ago. If I were you I'd leave ppu pin 17 wired up to system ground just to see if it gives you jailbars.

i finished wiring the scart socket today. everything works except one thing, ive got weak sync. i get a rolling b/w picture.

i got this on my jvc x eye until i did two things. i added a 220uf cap on the sync line and i also had to run it through the cxa1145.

i think i made an error when i wired the sync direct to the socket and not through the amp.

ive also got no audio through the scart port but i suspect my rca breakout box is looking for ground on a certain pin and it isnt there.

also, im not using a scart tv. im using a scart to yuv box and running it through component.

would an lm1881 fix the sync issue? also, what cap is the sync line really looking for?

one thing i forgot to mention. I still had bad problems with s-video on my Snes and a few other systems as well. i never could fix the interference.

ive since converted them all to rgb over component, and the artifacts and interference just melted away.

my snes had ugly checkerboard patterns that would only show up in certain stages, in certain games, and some games had none at all. it drove me nuts trying to locate the source. and i ended up buying a 60.00 sheilded multi-out cable figuring it was interference between chroma and luma. that cable didnt do a thing.

then i realized it was just something about those games that the svideo didnt like.

component cleared this up so much when i decided to do an rgb nes, svideo wasnt even an option at that point.

You mean the diagonal line issue found in the s-video signal of every snes? Every model of the snes has this issue I fixed it by adding a fairly strong resistor to the chroma line (something around 450 ohms did the trick). Surprisingly the colour saturation on the snes doesn't actually start to get weaker until you go stronger than 450-470 ohms so adding the resistor clears almost all of the interference and the picture still looks great. It's just an inherent flaw found in all models of the snes. Even when I installed my own video encoder into the snes I still needed to do that trick to fix it. And I do suggest you wire up a lm1881 circuit that will make sync work perfectly with everything. I got sync working on my old video encoder using a 220 uf cap pointed the same way that the caps are pointed in the rgb lines....but many years later I built a cxa2075 circuit that didn't need this cap on the sync line so I think the old video encoder board I was using was just poorly designed. Now that I think of it back in the day when I encoded the rgb from the snes externally into s-video I still had that diagonal line issue (until I messed around with it and discovered the resistor on the chroma line trick).

Needing a lm1881 and / or an amp depends on the device you have it wired into. I've never wired the sync from the rgb ppu through an amp and always managed to get a working sync signal straight from the chip. I found that anytime I had a sync issue with any system the lm1881 circuit always made it go away. I've never had a scart to yuv box in my posession so I havn't got a chance to play with one and learn what signals it needs. However I'm almost certain that if you have a sync issue the lm1881 will fix that.

Also regarding video issues older analog consoles have a lot of flaws in video signals that are impossible to 100% get rid of. Luckily it's possible to find ways to clear up the interference enough that it doesn't show up at all on your tv. A perfect example is the rgb nes / famicom jailbars:









All of these images were taken from the same system. It's just my capture card picks up a lot of interference that doesn't show up on my tv. Also keep in mind that this's a game running on the powerpak since the powerpak actually causes the jailbars to increase a little. In terms of jailbars this's actually as clean of an image as you can possibly get from any model of the nes. Luckily these bars don't show up on any of my tvs and all of my clients with their new high tech flatscreens also had a very jailbar free image.

hey, thanks for the help. i thought that i might need an lm1881 so i ordered 1 with the other parts. just didnt put it in.

this nes is giving the same issue my x-eye did. same rolling b/w picture.

on that system i had to change the sync pin on the multi-out to put it through the cxa1145 amplifier first. that cleared up the issue.

that was probably the easiest thing ive wired up in a long time. one wire fixes the problem. heh.

mvsfan wrote:

hey, thanks for the help. i thought that i might need an lm1881 so i ordered 1 with the other parts. just didnt put it in.

this nes is giving the same issue my x-eye did. same rolling b/w picture.

on that system i had to change the sync pin on the multi-out to put it through the cxa1145 amplifier first. that cleared up the issue.

that was probably the easiest thing ive wired up in a long time. one wire fixes the problem. heh.

Yeah I've never used one of those scart to yuv boxes but from my experience using a lm1881 made sync work with all of my encoders. The kits I order from japan come with a lm1881 built right into the kit circuit.

okay, i installed the lm1881 today, but i still just get rolling b/w picture. only difference is that now theirs no snow and it rolls a lot slower.

I wonder if i still need that 220uf cap on the sync line after the 1881? im going to try taking it out tomorrow and see what i get.

at least now, this project is just something to poke around at. im so close. im not going to work late on it anymore.

youve been a lot of help, drakon.
thanks.

before i put the electrolytic cap on the scart port, i took apart a dreamcast scart cable to see wich way the cap was pointing. but since im using scart to scart, and the port on the nes is an output, I concluded that i would have to flip it the opposite way to have the polarity right. i didnt need to. instead i got it backwards.

will flip tomorrow and retest. this *should* be the problem.

I use the almight game console RGB scart cable diagrams website

http://members.optusnet.com.au/eviltim/gamescart/gamescart.htm



NTSC snes scart cable has the positive leg facing the console and from my memory that's also how I wired up the cap to sync on the ppu. Again there's no way I can troubleshoot this unless someone mails me one of these scart to component converters (ironically my early nes powerpak troubleshooting was accomplished because someone mailed me his powerpak to play around with it).

And I don't mind helping people who've clearly done their homework and are willing to try things on their own. Also it's nice helping someone who actually listens to my advice.

well, i started out doing arcade projects. i built a mame cabinet myself about 6 years ago and i also restored a strikers 1945.

one reason i actually wanted to go with scart for my consoles is because i could add a scart port to the cabinets too, wich i did. i can plug all my consoles into them now.

btw, i dont mind listening when someone has the knowledge to help.

btw, the box im using for scart to yuv was 50 bucks on ebay. from what ive heard though it only works good with crts because it doesnt do any scaling.

if only i could find a schematic of the darn thing i think id know whats going on here. truth is i dont even know who makes the box. it doesnt say.

i just rewired the sync circuit again.

the sync is wired like this. PPU - lm1881 - ultimarc amp - pin 20 on scart. ive had it with no amp, through the amp, with the lm1881 and without it also with and without the cap on pin 20.

no difference at all. still wont sync. im out of ideas for the moment.

the brand new scart cable ive got is garbage. i took it apart and the wires are all crimped not soldered and they were crimped badly. the sheild is also not connected to anything. its basically a big antenna.

so i got to see arkistas ring in rgb. its neat looking. the American Sammy logo is miami hurricanes colors orange and green.

thanks for the help, drakon.

i wasnt able to keep the picture up for long because of the loose connection in the cable. it looks like my internal sheilding worked. i didnt see any jailbars at all but the cable sheild not being connected definately explains the rf interference waves that i did see.

thanks for all the help.

So....you finally got it working?

i think so. when i wiggle the cable i get a picture. its just a cheap cable. i didnt pay a cheap price for it though. im sending it back.

mvsfan wrote:

i think so. when i wiggle the cable i get a picture. its just a cheap cable. i didnt pay a cheap price for it though. im sending it back.

Interestingly enough I started modding consoles because of a cheap snes s-video cable. The cable was wired wrong it was somehow getting s-video from the composite video pin. That's how it all started with me.

i just picked up a 6 foot altona cable on ebay. it should do the trick.

so, this project is done unless i see something else after i get the new cable.

the rgb lines are sheilded from the point where they leave the ppu into the amp and also sheilded leaving the amp going into the scart socket. if i get any interference at all i will sheild the amp itself, and i am trying to work out a way to sheild the 1/8 inch coming out of the ppu for next time. im thinking about dipping a thin piece of metal in that stuff that makes rubber grips for tools.

second thing - i almost destroyed the amp trying to get that db9 off. i busted 4 through holes wich is why i had to solder red to the ic. the spot where i put the amp in the case theirs plenty of room without reducing the amp.

Glad it all worked out for you

theirs only one thing id like to find now - a clear case!

i still cant get sync.

that scart to yuv box works with all my other systems so i know its something in the nes.

i also got a new altona scart cable. its a straight through pin to pin cable and everything is wired right including the sheild and every connection is soldered instead of just crimped.

next, im going to try something i read from mooseman, and hooking pin 21 back up to the board and tapping sync off of the old composite video jack.

first though im going to check my sync wire for continuity.

thats for tomorrow though.

I hope that works. All of my video encoders didn't need the sync to be "amped" like moosmanns circuit has it. Is the component converter expecting you to feed it voltage over the scart connector like a scart tv would be expecting voltage?

im going to have to check my other cables and see if they have the switching circuit hooked up between the console multi out and the scart connector.

i really wish i could find out who makes this box so i could get some schematics.

also have tried turning the pots inside. one is for red, one is for blue, and i have no clue what the other pots are for. they dont appear to do anything at all.