A couple months ago I started a project to make a NES clone circuit board that uses the original CPU and PPU chips. I'm hoping this PCB will be 100% compatible with NES games and accessories.

The official Nintendo NES systems had various annoyances.
The front loader had a poorly designed ZIF connector and lockout chip.
The top loader had only RF video out.
I know mods are available to fix most of these issues, but I see them as a band aid fix.

I have designed Atari s-video mods in the past and was looking for more of a challenge.

The PCB I'm designing will correct these flaws as well as add new features:
1. Top loader with gold plated contacts, should be compatible with Game Genie and the Powerpak.
2. Can use either composite or RGB PPU chip and has on board amplifiers.
3. Better sound amplifier that can output stereo or mono sound. Has on board gain adjustment for each sound channel. 3rd sound channel from Powerpak or Famicom cart converter can be mixed in as well.
4. 2A switching voltage regulator can also provide 5v to video encoder board (for RGB.)
5. Fits in Polycase AG-85 case
6. Smaller size

I hope to have a prototype board ready for testing in early November.
I'll try to update my progress weekly, assuming there is progress.

sounds cool, looking forward to updates

Sounds like an ambitious project! Are you finding many donors for the CPU and PPU, or how does that work? What will you use for top loading connectors, NES101's?

this combined with the homebrew PPU could be very cool

Does someone owe you money? Why would you want to repossess a board?

Haha nice one! I didn't even notice the first (or second time for that matter) time I looked at it

I am definitely subbing to this thread keep us posted.

Very interesting indeed. I'll be watching.

I would suggest having a Famicom cartridge port in addition to a 72 pin NES port. The only thing to consider is you would not want to have two carts plugged in at the same time. Physical barriers could be used somehow. The Twin Famicom won't allow you to switch to disk mode if a cartridge is inserted.

I second this for sure. A simple slide switch with a plastic stop would be all you need.

I'm not sure what the correct abbreviation of reproduction is, repro? Anyway I corrected it. It seems no matter how many times I proofread my posts there's some little mistake in them, lol.

The CPU is the same on all vs. arcade boards, Playchoice, and the NTSC Nintendo consoles, these can be ordered from Mike's Arcade I believe.
The RGB PPU can only come from a Playchoice 10, vs. Duck Hunt, or vs. Tennis.
The composite PPU is from a NTSC NES or Famicom.

Careful desoldering can yield a cheap CPU and composite PPU from a NES or Famicom. I was able to do it with a 40 watt soldering iron and cheap desoldering pump.

I found a great replacement for the original 72 pin cart connector at Digikey, part # A31721-ND. I tested it and it works. No gutting game genies or top loader NES systems necessary.

My original plan was to include Famicom and NES cart connectors, but it would have made the board too big to fit in the case I wanted to use. Everything BARELY fits as it is. You can always use a famicom cart converter though.

One problem:
I'm not quite sure what diode arrays DA1-DA4 in the NES do exactly, they are connected to the controller port pins. They are not present on the Famicom from what I can tell. I wasn't able to find a replacement for this yet, any help would be appreciated.

My plan is to order 3 prototype boards and do some thorough testing. I'm reading up on any technical info I can to make sure these work. If there's a problem, I'll revise the design.

Nice project. Sounds a lot better than my idea (I was planning on going to an original toaster NES, yanking out the cartridge loader, cutting a hole on the top, and putting in a top loader cartridge slot) lol.

Couple questions: will the controller ports be spaced the same way, and will it support high-quality audio (like Mr. Gimmick)?

Can't wait to see what you come up with!

You've already got me sold. Subbed. And custom PPU seconded.

Probably just voltage protection.  Famicom with its hardwired controllers wouldn't need it.  Are they there on the AV Famicom?

How will you make the gold plated connectors? That stuff isn't exactly cheap to produce.

Will this replacement NES be made in production runs when it's done? It'd be pretty cool to own a modern and fully compatible NES clone.

It wont really be a clone, considering it requires you to supply the chips from an actual console.

sounds cool, good luck brining it to fruition. Depending on cost I'd be down

I don't really see the point then if the original systems have to be killed for those chips...

So you can have 10x better AV and such, and then better cart slots too.

I doubt it'll be 10x better if it stil uses the composite chips (using rgb is something else, yes I know that chip is also supported).
There's room for improvement but I doubt it'll matter THAT much.

Yeah, that was a dramatization, but it will be better.

If I could simply find an NOAC that doesn't swap the 25% and 50% duty cycles, I'll be a happy camper. I really don't like the idea of destroying consoles to build this. Maybe you could also work on programming an NOAC that doesn't suck into an FPGA chip. Have a third socket on the board for the FPGA, and just leave the CPU and PPU sockets unpopulated. Then you can use the "no vintage hardware was harmed" disclaimer.

To do that he'd need a bunch of logic level converters and stuff. In which case it's just alot (ALOT) cheaper to do everything on the fpga and just ditch a cart slot interface.

Presently I think the only way to build a NES with 100% compatibility and correct sound is to use the original CPU/PPU chips. I'm sure modern replacements could be made that are fully compatible, just nobody has managed to do it yet. I don't feel too bad removing the CPU and PPU from a NES since they're not that rare. The NES I removed the chips from had a bad memory chip anyway.
I recently got a Playchoice 10 PCB and it worked and was in really good shape so I can't bear to remove its chips.
I did get a Nintendo Vs. Duck Hunt PCB also, so I'll be able to test RGB output using its PPU.

I'm looking forward to that FPGA based PPU replacement project though. The RGB PPU is getting somewhat rare (and expensive.)

The only thing I have left to do on the Super 8 circuit board design is add the ground plane.
Hopefully I'll be able to order some prototypes next week.

I had room left over, so I left the diode arrays and provisions for the 330pf capacitors that connect to the controller port data lines. These may not be needed since they're only for ESD protection, I guess if you plug in your NES controller after dragging your feet across a plush carpet wearing fuzzy pajamas, it won't hurt the 74HC368.

I added a potentiometer for the auxiliary sound input, and fattened the 5v supply lines going to the CPU and PPU.
There's jumper points for the 3 available sound input channels so they can be configured a variety of ways. Stereo sound separation can be made adjustable by adding a potentiometer. If you don't like the NES "fake stereo," you can combine 1 and 2 with a low value resistor and get genuine mono sound.

I used the reset circuit from the Famicom since there is no lockout chip. The reset line of the CPU connects to a momentary switch to ground. Much simpler than the NES reset circuit. The reset line of the PPU is connected to 5v.

I did quite a bit of error checking so I'm fairly confident I didn't make any mistakes.
Ordering PCBs can be a gamble. You have to get it right the first time, otherwise you wasted the money.

I want to test the prototype board first with the CPU and PPU I removed from my donor NES. The top loader has issues with its composite video, so I'm hoping composite will be high quality on my board.

I'm not sure how I will mount the controller ports in the case yet, I'll have to worry about that later. I ordered some NES controller ports from Parallax so hopefully I can mount them in the case and have it look good.