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 The rgb / s-video / stereo sound famicom

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Drakon
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PostSubject: The rgb / s-video / stereo sound famicom   Sat Jan 05, 2013 10:27 pm

*edit* Final video:



Old worklog stuff:

This's still a work in progress:





what I learned from working on this:

You can completely remove the rf box and run the system using just the regulator and power jack, I also soldered in the original fuse just to be on the safe side.

Relocating the rgb kit to the back and having the rgb signals travel to the back adds a lot of interference to the image (jailbars and such), which means I'm going to have to wire up all 40 ppu connetions by ide cable (shouldn't be a problem) so I can fit the kit in the back.

The case of the original famicom is freaken tiny, making things fit inside of it is a nightmare.

What's left to do: A lot of things, you'll see as it comes along, I still havn't wired up the upgraded audio circuit but that shouldn't be an issue.


Last edited by Drakon on Fri Jan 18, 2013 11:37 am; edited 2 times in total
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PostSubject: Re: The rgb / s-video / stereo sound famicom   Tue Jan 08, 2013 10:25 am



Brief description of what was done, this's the most detail I can go into:

I desoldered the rf box, from the rf box I desoldered the power jack, 7805 regulator, regulator heatsink, and the fuse. I built the regulator, fuse and heatsink into a small piece of protoboard and wired it into the ac jack / solder spots for where it powers the mainboard. Everything works, I bolted my miniaturized regulator circuit near the front of the case to make space at the back for all the upgraded stuff.

I built the av famicom upgrade kit from japan, the kit is designed for the av famicom but you can get it working in other models of the nes / famicom. I translated the instructions from japanese so I can build this japanese kit. The kit is the "heart" of the system. The kit contains an audio circuit that highly improves the system audio. Unfortunately this kit is designed for the av famicom audio circuit so it sounds different on different models depending on their audio circuit. The av famicom audio circuit is unique and I'd like to someday figure out how to recreate it. This famicom is a something-something-gpm-02 which is similar to the av famicom audio circuit except it has a bigger low pass filter. This means that this famicom has more bass but sounds a tiny bit more muffled (not a huge difference though), the end result sounds great with the audio circuit on this kit.

The kit also lets you socket a rgb compatible ppu chip and it contains a cxa1645 video encoder circuit which amps the rgb and converts it into s-video. You can't use the nes / famicom standard ppu chip you need a compatible chip which outputs rgb (the ones used in arcade machines). Without a nes compatible rgb ppu chip you won't be able to get rgb or s-video from your machine. I highly modified the video circuit to produce much better quality s-video. The only place to fit the kit was in the back where the rf box used to be. I had to relocate the entire ppu socket (all 40 pins) to the back. I tried just relocating the rgb, sync, 5v and ground lines to the kit and it worked but adding the extra 5 or so inches of distance between the ppu and the video encoder added big annoying jailbars to the image. What's great is this seems to be the fix for jailbars in the rgb nes / famicom, the less distance between the rgb ppu and the sony cxa2075 video amp / encoder the less jailbars you get.

As mentioned earlier I made some upgrades to the av famicom kit, I upgraded the video encoder from a cxa1645 to a cxa2075 which produces sharper s-video with better looking colours. I also built a small circuit that divides the master clock signal down to the right speed to drive the video encoder, this fixes any colour bleeding in s-video.

I removed the 74ls373n and installed a precision socket where it used to be. I dropped in a 74hc373 chip so my powerpak will run with the rgb setup. Credits go to acem77 for discovering this fix:

http://forums.nesdev.com/viewtopic.php?t=4016

If you look at the playchoice schematic / pcb, the playchoice (which uses the same rgb chip I used) has the 74hc373. Still I'm very glad I didn't have to try and figure it out on my own.

I wired up the famicom with nes controller ports. The famicom controller headers use the same pinout as nes controller ports except the famicom has an extra pin for the microphone (which is unused so I just ignored it).



"p4" is player 1 and "p5" is player 2. This schematic arranges the connections in the same order that the pins are arranged on the famicom pcb making it very easy for me to figure out the wiring. I also probed the connections to be extra sure I was getting everything right.

A couple of games sound funny with the kit audio circuit so I wired up a switch that lets you real time switch between the kit audio circuit and the default famicom audio circuit. I didn't have room in the tiny case to fit all the new sockets so I have them hanging out the back and I'll build them into a project box when I pick one up.

The new external ports include:

NES player 1 and 2 controller ports
S-video jack
RGB + sync wires (going to wire them into a model 1 sega genesis rgb port)
Stereo headphone jack (I could wire the audio output into rca jacks if I prefer still havn't decided)
Switch to go between default and upgraded audio

The power jack still sits inside the case I cut a small hole for it in the corner.

What I get from all these mods:

True rgb and s-video using all original nintendo parts (no fpga / clone / emulation)

A much improved audio circuit that has stereo separation and fixed bass / volume balance levels.

Kirkys adventure and tmnt 2: the arcade game some of the popping drums get filtered out so I built a switch to go back to default audio for these two games

NES controller ports in a famicom, no more stupid hard wired controllers.

To summarize, one awesome famicom.
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PostSubject: Re: The rgb / s-video / stereo sound famicom   Wed Jan 09, 2013 8:15 pm

Annnnnd it's done:





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