Making a repro game for the Wonderswan is actually quite easy – but as with a lot of mods, there are a ton of things to consider. I’ve learned this method from the user remysharp on Reddit: https://www.reddit.com/r/WonderSwan/comments/1670705/been_making_my_own_carts_via_chip_swaps_and/
With the method I’m about to describe, you will need an original game to be sacrificed and a MX29L3211 eprom (and programmer) to swap with.
The first thing to think about is what game you want to make a repro of and check what type of save-chips it uses. It can be sram, eeprom or no save at all, and then match this with a donor game that use the same save-type. The easiest way of doing this is to load up the ROM in an emulator and check what type of save-file the emulator creates. Unfortunately, Wonderwitch-games such as Dicing Knight and Judgement Silversword can’t be made by using regular games as donors.
There is one more thing to check before we can get started – and that is the size of the ROM-chip in the donor game. AFAIK they can come in two sizes, and MX29L3211 can only be used in a cart with the big chip. Out of three crap games I had, only one of them could be used as a donor:
I found this page, that has a list of PCB type and save types of most (all?) games: https://web.archive.org/web/20240421042736/https://blog-imgs-131-origin.fc2.com/o/t/o/ototo2009/WS-2019-12b.html
So you can check that page for the game you want to make and match it with a crappy game that use the same save-type. The game I used for my Rockman WS was Senkaiden 2 / Senkaiden Ni. According to the list the PCB-type is PTS-0108, so look for that or other games that use that if you want a good donor for games with SRAM. The other games on my picture are Inuyasha: Fūun Emaki and Inuyasha – Kagome no Sengoku Nikki – Both use PTS-0133A PCB, so we can confirm that PCB can’t be used to make repros this way.
If you’ve got a donor ready, the next step is to program the new game to the MX29L3211. I chose the fan translated english version of Megaman WS, which is a 4MB ROM-file that takes up 100% of the eprom, it was just a straight forward flash to the eprom. But if you want to use a smaller ROM you have to put it in the end of the eprom memory. For example: if you have a 1MB ROM-file, program it from 3-4MB on the eprom.
Now it’s time to remove the old mask-rom. I used a fine cutter to cut off all the legs, and then just “scrape” off the remains of the legs with a soldering iron and solder wick. Clean up with IPA, put some flux and new solder on the pads and put the MX29L3211 in position. Lift pin 1 (WR) and solder down the rest of the legs. Then take a small wire and solder it from pin 1 (WR) to pin 23 (VCC) – this is done because the normal state of the eprom is to be written to, so you need to keep pin 1 high to be able to read from the chip.
And that’s it, now you’re done!
Enjoy your new Wonderswan game!
