Rockman 4 Minus Infinity repro guide
The past few years I’ve picked up the hobby of repairing old game consoles, modding them for things like region-free gameplay or RGB output options for the best possible video quality.
One of the things I heard about along the way was a romhack called Rockman 4 Minus Infinity, an amazing hack that redoes the entirety of Rockman 4/Mega Man 4. Most people will probably play this on an emulator because the de facto flash cart, the Everdrive N8, doesn’t support ROM files of this size. The creator has said though he plans to release a new version of the N8 that supports larger games like this.
So, enter the 8-bitter from Voultar. Assuming you have experience with a soldering iron, it’s an easy solution to use to apply translation patches and romhacks to real NES and Famicom cartridges.
But I specifically wanted to make my own copy of R4MI. The only problem is most of the information online is using old methods of wiring messes before a solution like this existed. Not that they’re bad, they just haven’t been updated for modern methods.
And while Voultar’s video covers just about everything you need, he didn’t go over the process of replacing CHR ROM with CHR RAM.
So I spent several hours hitting various forums and sites to gather information on how to make my own. This guide serves as a way to demonstrate a fairly modern way (though there are probably a few things that could be cleaned up) to do this in 2019.
What you’ll need: (the below is image heavy)
- Soldering tools (iron, solder, flux)
- Desoldering gun (not required, but highly, highly recommended). If you don’t have one, then get a desoldering pump and desoldering braid and lots of patience
- Security bit screwdriver to open NES/Famicom/Super NES/Super Famicom cartridges
- 8-bitter with memory chip
- Donor cart with MMC5 mapper with save support. Use the NesCartDB to find one suitable. I’m using the Japanese release of Nobunaga no Yabou: Bushou Fuuunroku (信長の野望 武将風雲録 ), but I’ve also used Sangokushi II (三國志Ⅱ) with no changes from what this guide will show
- Donor cart with CHR RAM chip OR compatible CHR RAM replacement. I used Ginga no Sannin (銀河の三人). I’ve read the AS6C6264-55PCN is a drop-in replacement, but have yet to try it. Can be found at DigiKey as “1450-1036-ND”.
- ROM file of Rockman 4 with the Minus Infinity patch applied. You want version 1.01. There is a bug of some sort in 1.00 that keeps popping up the weapon select screen.
- Replacement CR2032 battery (or battery holder with standard CR2032 batter). Most likely the one in the cartridge will the 20+ years old and may not hold your save data for much longer.
This guide is going to assume you have your chip programmed with the patched ROM. If you’re not sure how to do that, watch this instructional video by Voultar first. The principles shown apply to doing the work in this guide.
OK, so now that you’ve watched the video and have an idea of what we’ll be doing,
First, before doing anything, test both donor carts to ensure they play without issues. If there are problems you can’t fix, the cart(s) may have issues and you’ll need new ones. Best to start with working donor carts.
I’ll start with the MMC5 donor cart first. Using the security bit screwdriver, we’ll open it up.
If you see damage on the edge connectors, you’ll either want to find a way to repair this or get a new donor. I say this because one donor cart I was going to use had some rust and corrosion going on.
Notice in the picture above the bottom left chip. That’s a mask CHR ROM chip that’ll replace with a CHR RAM 28-pin DIP package. So let’s flip it over.
When you flip it over, the chip will now be on the bottom right. Remember that, or you could be working on the wrong chip!
Before soldering, I highly recommend adding flux and fresh solder. The stuff that’s on there is old, quite possibly lead-free, which means higher melting temperature and a bit harder to work with. The picture above shows what it should look like.
After making quick work of it with your desoldering tool, you should have your pins free and wiggling around. Then you should be able to pry the chip out without any real force needed, leaving all vias intact and without damage on either side of the board.
So with that old CHR ROM from your donor MMC5 game removed, we’re ready to work on getting our CHR RAM from a donor. You can choose to keep this (CHR ROM) if you think you’ll ever want to undo this whole thing and return back to the original game… or you can dispose of it.
If you already have a CHR RAM or known drop in replacement that works, you can skip down a little bit.
The CHR RAM donor game I’m using is Ginga no Sannin (銀河の三人).
Unlike with the other donor game, we’re not concern about the cartridge pins or anything on this board other than our CHR RAM chip. After we’re done, this game won’t be usable anymore until a compatible CHR RAM chip is put back in.
The next step is to remove the CHR RAM. When looking at it from the front, it’ll be the chip on the left. But when you flip it over, it’ll be the chip on the right.
As with before, add some flux and new solder to aid with the removal process.
Next, we need to go back to our MMC5 donor cart and remove pin 31 of the PRG ROM from circuit. We can either cut the pin or desolder it. I chose to desolder and pry the pin out.
Regardless of whether you desoldered like I did above or simply cut the leg, left it up and then bridge it to pin 32. You can simply use a solder blob like I did (shown below), or a small jumper wire if you’re having trouble.
After that’s done, we’re done with all the desoldering! Well, unless you really screw something up.
Now we need to prep our CHR RAM we removed from the second game. This is the 28-pin DIP. You’ll need to lift up pins 1, 22, 26, 27 and 28. I’ve read that pin 1 is NC, so you might be able to leave it down, but I lifted it.
Important to note is that the CHR ROM we removed was 32 pins and our CHR RAM we’re putting in its place is 28 pins.
We’re going to solder to wires to vias 31 and 32, so go ahead and fill those is with a bit of solder.
PLEASE NOTE: Depending on if you’re using a 60-pin Famicom game (as shown in this guide) or a 72-pin NES game, this next part will differ slightly.
Also, a tiny via is available that we’re going to solder for connection to cartridge connector pin 47 (PPU /WR). If you’re using an NES game, I believe, but am not 100% sure, you’ll want to connect to pin 56 (PPU /WR). There may be a via for you to connect to for this. If not, use a multimeter to tone out a suitable point to solder a wire to.
Now, let’s go ahead and solder in our CHR RAM with the lifted pins.
MAKE SURE YOU PLACE PIN 1 OF THE CHR RAM INTO THE OLD PIN 3 VIA. That is, after the chip is in, you’ll have four vias to the right that the chip doesn’t go in. The chip should fill up all of the holes on the left. I forgot to take a picture of this. If you’ve gotten this far, hopefully it’s all making sense. And if you already filled in the vias I mentioned above (31 and 32), this shouldn’t have been an issue.
After I soldered our donor CHR RAM chip, I further bent back pins 24, 26, 27 and 28. The reason is when I place the board back in the plastic cartridge shell, they got in the way. You could choose to snip off part of these, but I went for non-destructive.
Let’s leave the CHR RAM alone for now and move on to getting our actual data for Rockman 4 Minus Infinity installed with the 8-bitter.
You’ll need your 29F800 chip already programmed. That’s outside the scope of this guide, so please refer to the walk-through video shown above. You know, the one I told you to watch before continuing with this guide.
These are small parts though, as illustrated with the centimeter ruler and the nano SIM (for comparison).
We’re going to take the 8-bitter and solder it onto the BACK of the MMC5 donor PCB. Align the top left (above Mario’s head) that has the white half-circle to the placement of pin 1 of the CHR ROM. The video already mentioned shows this.
After it’s in place (or before, it’s up to you), solder the three jumpers with the designation of “MMC5”.
Now that it’s in place it’ll be easier to solder in our TSOP flash memory (29F800).
The final result of the CHR ROM work should look like the above. Now let’s do a quick test. Yes, I know, CHR RAM isn’t finished. This is just a test to check CHR ROM.
Place the game into your Famicom/NES, and turn it on. If everything is soldered into place, the game should start, but with garbled graphics (because we don’t have CHR RAM set up yet). The first 5 – 10 seconds won’t have sound, but you should see something on the screen. After that, you should get music.
If all you get is a black screen (or something else), check your soldering! Make sure the 29F800 is soldered in correctly. Check for bridges, ensure that all pins are soldered in place.
Once that is done, remove the game and let’s finish up the CHR RAM.
We need to connect the following:
|Pin on CHR RAM||Via/hole on PCB|
|Pin 24||Via 31|
|Pin 26||Via 32|
|Pin 28||Via 32|
|Pin 27||Cartridge pin 47 (Famicom) or 56 (NES)|
Here are pictures to illustrate.
I soldered the jumper wire from pin 24 to via 31. That’s the blue wire in the picture.
To connect pins 26 and 28, I ran a jumper wire between them, and then from 28 to via 32 on the PCB. These are the gray wires.
And for pin 27 to pin 47 (Famicom; probably pin 56 on an NES donor game), I ran the purple wire to that extra via.
Here are some pictures at different angles to illustrate.
Next, I swapped out the old CR2032 battery. I didn’t see a manufacture date on it (SFC/SNES games often have these stamped on), but I imagine it’s 20+ years old. And because R4MI has battery back-up, I replaced the battery. Unfortunately the only one I had on hand was a cheap Chinese one. I won’t be surprised if I have to replace this later.
And with that, all of our hard work is done! Your finished board should look something like the above. Put it all back in the plastic shell, put the screws back in, and you’re finished.
This guide might work for other MMC5 romhacks, but I really have no idea and don’t have interest at this time in finding out. But if it does work, please let me know and I’ll make a mention here.