This is my design of a flashable MBC3-based cartridge for the Game Boy. The MBC3 mapper improves a lot over the MBC1, and includes a real-time clock for everyone's favorite battery-sucking game.... Mary Kate and Ashley Pocket Planner! Oh, and Pokemon.
This circuit board should cover most, if not all, MBC3 games. The features are as follows:
- Able to make games up to 16 Mb in size, that use up to 256 Kb of RAM
- Compatibility with all four of the popular Game Boy battery management ICs - MM1026, MM1134, BA6129, and BA6735
- The option to add battery backup to the cartridge without the need of the original battery management ICs
- Fully compatible with the GBxCart RW so you can transfer games and save files to and from the board
All gerbers and source files can be found in this repo, as this project is fully open source. Technical documentation of the board can be found in the Technical folder.
- To make this game, you need to have an original Game Boy game that uses an MBC3 mapper chip. You can find a list of games and their mappers here. Use the search function.
- You will need to remove the MBC3 from your donor cartridge for use on this board. This will require a hot air rework station or a hot plate. There's a list below of other parts you can re-use from the donor cartridge.
- When soldering parts on, it's a good idea to put kapton tape or otherwise cover the bottom cartridge edge. You do not want to get solder on the cartridge contacts.
- I am not responsible for any damage you do to your self or your property. I do not guarantee design compatibility. You may encounter issues with certain games! Attempt this project at your own risk.
- If you are using this board to make games other than for personal use, you must have permission from the originator to use and distribute any ROM images or other related material. You are responsible for making sure you adhere to any license requirements.
DO NOT use my circuit boards for profiting from stolen work - this especially includes homebrew content, ROM hacks, and using fan-made labels without permission from the originator. Support original creators!
Please note that version 1.3 is technically untested, however, the only consequential change is an additional 0.25 mm on the bottom of the board edge for better fitment, so I don't expect issues.
The zipped folder contains all the gerber files for this board. The following options must be chosen when ordering boards for yourself.
- Thickness: 0.8mm
- Surface Finish: ENIG
- Gold Fingers: Yes, 30° chamfer
Add this note to orders: "The milling.gbr layer indicates where an unplated slot should be added to the board. Please add an unplated slot as indicated."
Currently not selling on Etsy, but will in the future. Stay tuned.
You can use the zipped folder at any board fabricator you like. You may also buy the board from PCBWay using this link (disclosure: I receive 10% of the sale value to go twoards future PCB orders of my own):
The board is also listed on OSH Park as well. Be sure to get them in 0.8mm thickness if you order from here.
The EEPROMs on the board needs to be programmed somehow. I recommend using the GBxCart, as mentioned. These boards are fully compatible with it, and it makes reflashing games extremely easy using lesserkuma's FlashGBX software.
Alternatively, you can buy an EEPROM programmer with a TSOP adapter. The downside to this method is that you have to desolder the chip every time you want to program it. The FlashcatUSB is one popular option in retro spaces.
When assembling a board, I recommend populating all the parts except the battery, and getting it to run initially without it. This is to make it easier to fix any solder connections that might need fixing, without having to worry about getting the battery hot. And if you need to rework anything near the battery after you've put it on the board, be safe and remove it before putting a hot soldering iron next to it.
And this should go without saying, but if you're assembling these boards with a hot plate or hot air, do not solder the battery on this way. You should use an iron, and keep heat off of the battery as much as possible.
(Also check polarity!)
The board comes with five sets of jumper pads for solder bridges. SJ3, SJ5, and SJ6 require you to solder bridge the middle pad either to the left or right pads. SJ1 and SJ4 are configured by either leaving them alone or bridging them with solder. Here are the situations where you need to add solder bridges.
Solder bridge SJ1 and SJ4 if your game does not use any SRAM or battery. I don't believe there were ever any MBC3 games made without SRAM, but if you wanted to... remove it for some reason, you can.
The MBC3 chip you use from the donor cartridge can be one of a few different types:
- If your MBC3 doesn't have a revision letter on it (it just says "MBC3" on it) then bridge the middle pad of SJ3 to the left. (You will also need to populate Q1!)
- If you're using a revision-less MBC3, and are making a game that requires a battery, you should use a donor MM1026, MM1134, BA6129, or BA6735 battery management IC instead of the replacement TPS3613.
- If your MBC3 does have a revision letter, such as MBC3A or MBC3B, then bridge the middle pad of SJ3 to the right.
[Images of MBC3 chips from Game Boy Hardware Database.]
These jumpers are located underneath the MBC3 chip, and labeled "64K" and "256K". Solder them to configure the amount of RAM your cart uses. You must configure these pads for every game you make, unless you do not need RAM. You can find a list of games here with their respective RAM sizes.
- If the game you're making uses 256Kb of SRAM, then solder the middle pads of the two jumper sets to the right pads.
- If the game you're making uses 64Kb of SRAM, then solder the middle pads of the two jumper sets to the left pads.
- SJ5 and SJ6 must be soldered in the same direction.
- The footprint of these selection pads should allow for a DPDT switch, part number CAS-220A1, to be placed on these pads instead of having to bridge the pads with solder.
Note that you can make games that only require 64Kb of RAM and still use a 256Kb SRAM chip. You still need to configure the jumpers to the 64Kb setting, though.
On the back of the board are five test points. Here's where they are connected:
- TP1: SRAM supply voltage
- TP2: Battery voltage (after R1)
- TP3: Battery voltage (positive terminal of battery)
- TP4: Ground
- TP5: VCC input voltage
After you assemble your game, you should measure the current out of the battery. But first, you should program it with the GBxCart, or if you programmed the EEPROM separately, put it into a Game Boy and cycle power once. Then, flip the PCB upside down on a non-conductive surface (not your leg), and set your multimeter in DC millivolts (or volts). Put the positive probe on TP3 and the negative probe on TP2. If you used a 10kΩ for R1, as indicated in the BOM, you should read a voltage in the single or tens of millivolts for non-RTC games, or up to 40 mV for games using a real-time clock. If you have something much higher, especially voltages above 40mV, then you likely have an issue or short circuit on the board somewhere.
Note: If using the replacement battery management IC in U5, you need to power up the game at least once before battery currents will make sense.
The revision of MBC3 chip you are using will influence how much current draw you get, and thus how long your battery life will last. For the test set up, I am replacing the battery with a regulated DC power supply set for 3 VDC for consistency, on a cart board with an MM1134 chip for U4, and brand new AS6C62256 SRAM.
| Rev | P/N | Current draw (no RTC) | Current draw (with RTC) |
|---|---|---|---|
| MBC3 | LR385364 | ? | ? |
| MBC3 | BU3631K | ? | ? |
| MBC3A | LR38536B | ? | ? |
| MBC3A | BU3632K | ? | ? |
| MBC3A | P-2 | ? | ? |
| MBC3B | BU3634K | ? | ? |
| MBC3B | P-2 | ? | ? |
Your parts list will vary depending on the game you are trying to make, and what chips you have for the battery management (if any). Note that C9 - C11 footprints are only included for edge cases that may require them; you can ignore them unless you run into issues.
Please carefully review the parts you need for the board you are trying to make. Do not add any parts to your build that don't appear in the column for the game you are making. This means you cannot populate every component on the board at the same time.
| Reference Designators | Value/Part Number | Package | Description | No save carts | Save carts with U4 | Save carts without U4 | Source |
|---|---|---|---|---|---|---|---|
| B1 | CR2032, CR2025, CR2016 | CR2032 | Backup Battery | x | x | https://mou.sr/3SeAzfT | |
| C1 | 0.1uF | 0603 | Capacitor (MLCC) | x | x | x | https://mou.sr/3ENc15O |
| C2 | 15pF | 0603 | Capacitor (MLCC) | If using RTC | If using RTC | https://mou.sr/3PPorjO | |
| C3 | 15pF | 0603 | Capacitor (MLCC) | If using RTC | If using RTC | https://mou.sr/3PPorjO | |
| C4 | 0.1uF | 0603 | Capacitor (MLCC) | x | https://mou.sr/3ENc15O | ||
| C5 | 0.1uF | 0603 | Capacitor (MLCC) | x | x | https://mou.sr/3ENc15O | |
| C6 | 10uF | 0603 | Capacitor (MLCC) | x | x | https://mou.sr/3mZtSkF | |
| C7 | 0.1uF | 0603 | Capacitor (MLCC) | x | x | x | https://mou.sr/3ENc15O |
| C8 | 0.1uF | 0603 | Capacitor (MLCC) | x | https://mou.sr/3ENc15O | ||
| Q1 | 2N7002 | SOT-23 | N-Channel FET | If MBC3 no rev | x | https://mou.sr/3rgfh6J | |
| R1 | 10k | 0603 | Resistor | x | x | https://mou.sr/3riR7IH | |
| R2 | 330k | 0603 | Resistor | If using RTC | If using RTC | https://mou.sr/3PZ2pvj | |
| R8 | 10k | 0603 | Resistor | x | x | x | https://mou.sr/3riR7IH |
| R9 | 130k | 0603 | Resistor | x | https://mou.sr/3MjXliy | ||
| R10 | 49.9k | 0603 | Resistor | x | https://mou.sr/3Q3NRZO | ||
| U1 | 29F016, 29F032, 29F033 | TSOP-48, TSOP-40 | Flash EEPROM | x | x | x | AliExpress or eBay |
| U2 | MBC3 | QFP-32 | MBC3 Mapper | x | x | x | Donor MBC3 Game Boy cartridge |
| U3 | AS6C6264, AS6C62256 | SOP-28 | SRAM | x | x | https://mou.sr/450klcY | |
| U4 | MM1026, MM1134, BA6129, BA6735 | SOIC-8 | Battery Management | x | Donor Game Boy cartridge | ||
| U5 | TPS3613 | MSOP-10 | Battery Management | x | https://mou.sr/45Ir2kh | ||
| X1 | 32.768 kHz | Radial | Crystal Oscillator | If using RTC | If using RTC | https://mou.sr/3ZteKuy |
You can use a few parts from the donor cart on the new board to save some money. Note that you will generally get better reliability with new parts as opposed to old ones. For example: I have seen failed RAM chips from donors in the past.
- C2, C3, R2, X1: RTC Components - You can move over these parts if you're using the real-time clock function
- U2: MBC3 - This one is required
- U3: SRAM - You can use this part only if the game you're making uses the same or less amount of RAM that the donor cartridge does
- U4: Battery Management IC - Using this is probably preferred over the TPS3613 because it'll save you money and parts to put on
You could probably transfer over most of the 0.1uF capacitors but they're pretty cheap anyway, so I generally just recommend buying new resistors and capacitors.
- The footprint for the EEPROM is specifically for 29F016 - it has 48 pins. However, 29F032 and 29F033 are only 40 pin devices. They still work fine on the board though - place them in the center of the footprint, and leave the outer two pins on each corner empty
- The 29F016, 29F032, and 29F033 have been known to occasionally be defective upon arrival. They're either used, or new old stock, and usually only available from AliExpress.
- The footprint for the battery can fit a CR2032, CR2025, or CR2016 with solder tabs. The only difference is the mAh capacity (larger number = longer life). If you get Panasonic tabbed batteries, you may have to trim the battery tabs to make them fit on the footprint.
- For untabbed coin cells, you can find battery retainer adapters online, like this one.
- For battery management, use either U4 or U5 and supporting components. Do not use U4 and U5 simultaneously on one board. They will interfere with each other.
- Kb is kilobits and Mb is megabits. Sometimes you will find game ROM and RAM sizes defined in terms of KB or kilobytes and MB or megabytes. You can convert Kb and Mb to KB and MB by dividing Kb or Mb by 8. For example, 256 Kb = 32 KB.
- You only need to provide ROM and RAM chips that have at least or greater the size of the game you are trying to make. That means you can use a 256Kb SRAM chip for a game that only requires 64Kb!
- Extended cart edge down by 0.25 mm for better fitment
- Added OSHW logo and "SUPPORT ORIGINAL CREATORS!"
- Replace non-donor battery management circuitry with a TPS3613-based circuit for smaller BOM and easier routing
- Moved all parts on the top down to allow for compatibility with DMG-style shells
- Rotated battery for more space
- Widen SRAM footprint for easier soldering
- Renamed some reference designators for consistency between designs
- Changed silkscreen for clarity
- Prototype revision
- Jeff Frohwein's GameBoy Tech Page
- Game Boy Hardware Database
- Nintendo Gameboy Game List
- insideGadgets discord server for GBxCart RW compatibility requirements
- Lesserkuma's FlashGBX software
- System Reset IC Datasheet
- TPS3613 Datasheet
- Board outline modified from Dillon Nichols's Homebrew Gameboy Cartridge project
- Thank you to gekkio for their deep Game Boy knowledge resources, and for collaboration in demystifying some of the design choices on Game Boy cartridges
- Thanks to the awesome members of the Modded Gameboy Club for their feedback and support during the entire project development
This work is licensed under a Creative Commons Attribution-ShareAlike 4.0 International License. You are able to copy and redistribute the material in any medium or format, as well as remix, transform, or build upon the material for any purpose (even commercial) - but you must give appropriate credit, provide a link to the license, and indicate if any changes were made.
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