Author Topic: Nintendo + less wires = still fun?  (Read 25825 times)


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Nintendo + less wires = still fun?
« on: August 27, 2006, 08:18:45 pm »
Welp, with some desoldering, cutting, soldering, and more cutting, I now have an actual UNROM cartridge!¬† It has pretty much the same functionality as the jungle of wires version, though it'll still need a switch added in to toggle between horizontal and vertical mirroring (I won't get into explaining that this time).¬  For now, it uses vertical mirroring, which is fine, because that's what Contra uses, which was already on my eeprom.

For the sacrificial cartridge, I used Silent Service.¬  Not the worst game ever, but not the best one either.¬  Plus, I got it for 99 cents, so there you go.¬  Getting it open was kind of a pain in the ass, because Nintendo cartridges used those stupid security screws, and I don't have the screwdriver for it.¬  But, I took a tiny jeweler's type screwdriver, along with a really stiff piece of wire, and was able to force at the notches from both sides of the screw to get it to turn, and after a minute or two of this, you can get'em out.¬  Once you get the hang of it, they come out fairly well.¬  There's three in a cart.

Once it's open, this is what you end up with*:

* I forgot to take a picture before I modified it.  ^_^;  But this is almost identical.  Mine just had a capacitor on both ends, and used different model chips.

I should have also taken a picture of it after I removed the PRG rom (the one on the left in that picture), but oh well.¬  But anyhow, some rewiring was in order.¬  The PRG rom was just 28 pins, and my eeprom is 32 pins.¬  Even a 28 pin eeprom would have taken some rewiring, but in my case, I needed to fit a socket which was even larger than the board was designed to handle.¬  I actually started out with a 40-pin socket, which is all I had handy aside from a 28-pin one, so I had to cut it down to just 32 pins.¬  But after carefully planning out last night which pins needed to be bypassed and which needed to be reconnected elsewhere, I was able to get the socket soldered in place.¬  It was just the wires that were the hard part!¬  The only hook-up wire I have is 22 guage, which is thick and stiff.¬  I needed something thinner and flexible, so I used some wires pulled off an old floppy cable (the rest of which is what was used in my breadboard version).

You might notice the one cartridge pin is silver.¬  That's because I originally tried to use that for ground connections since it was closest, but it was wasn't going to work very well.¬  That wasn't the only thing that had to get rewired, though, because I realized it wasn't even going to fit back in the cartridge casing, so I had to redo another wire as well.¬  Also, I should have taken a picture beforehand so you could see, but the capacitor on that side of the board was just plain in the way.¬  It was right under where the end of the socket needed to lay.¬  So, I desoldered it, and put it back on from the back side of the board, as you can see on the left side of the second picture there.¬  I also took advantage of the +5v going into the one end of that same¬  capacitor, and used that for the top right pin of the eeprom for power, and also to hold the write line high since that pin was right below it.¬  I just bent the latter straight over on top of the power one and added a tiny dab more solder.

There it is in the NES with the eeprom inserted into the socket.¬  My surprise was the board actually working on the very first try.¬  I seem to generally have bad luck with electronics projects, despite my interest in them.¬  But it went really smoothly, and works like a charm.¬  I don't even get the sprite glitches like I'd get sometimes on my breadboard jungle version.

But now I wanted it back in the case.¬  The eeprom in the socket is simply too tall to fit back inside properly.¬  But that's nothing that an hour with my piece of shit dremel couldn't fix.

I replaced the security screws with a couple I found elsewhere.¬  It was hard finding some small enough to fit.¬  But there you go, a working UNROM development cart, running Contra at the moment.¬  You might even notice that the cartridge tray isn't in that NES, and nothing is pushing the cart down like you're normally supposed to.¬  That's because my refurbishing of the pin connector has it making such a good connection that even when the cartridge tray is in the system, you don't even have to push it down.¬  It's pretty strange to see that for the first time when you turn on an NES with the cart sticking up like that, and have it work just fine.¬  I didn't do that part today, though.¬  That was to get SMB/Duck Hunt working before, since I'm still forever playing those.¬  xD

There's a couple things or so on the todo list for this project.¬  First is adding in the switch to toggle between horizontal and vertical mirroring modes, since a game won't work properly unless it's set to which it was designed for.¬  The other thing I'd like to add is a toggle switch to switch between the upper and lower 128kb of the eeprom (since it's a 256kb chip).¬  The cart is just using 128kb at any particular time for the game, so it's capable of storing two games, just like my jungle board did.¬  On that, I just switched a wire from ground to +5v to switch between games, and a similar method for setting the mirroring.¬  The cartridge here though will take a bit more work.¬  And possibly a glue gun to put the switches in place, which I don't think we have!

I could also modify the board to run actual 256kb UNROM games, but there really weren't all that many of those, so I might not bother.¬  Final Fantasy 2 and Paperboy 2 are the only ones worth mentioning, prolly.

« Last Edit: September 03, 2006, 10:03:41 am by FyberOptic »