For decades, the Nintendo 64 Expansion Pak has been a source of both joy and frustration for retro gamers. Necessary for classics like The Legend of Zelda: Majora’s Mask and Donkey Kong 64, the small red-topped module has become increasingly expensive and prone to failure. Now, hardware developer Mason Stooksbury (known in the community as LambBrainz) has finalized a breakthrough for the scene: a fully open-source recreation of the Expansion Pak.

The project, which has been in development for over two years, aims to solve the “inventory gamble” of the second-hand market by providing a modern, documented blueprint for the 4MB memory upgrade.

From “N64-Killer” to Golden Standard

In late 2024, the community held its breath as the Swiss repair experts at Consoles4You issued a dire warning: early versions of the Open Source Expansion Pak were ‘N64-killers.’ Due to a symmetrical edge-connector design that could lead to a fatal short-circuit, the project faced its biggest hurdle yet. Today, however, that danger is a thing of the past. Thanks to a collaborative effort between original designer Mason Stooksbury and the technical team at Consoles4You, a safe, refined version of the Pak is finally hitting the market

The latest version, now available on Stooksbury’s GitHub, features:

• Full KiCad Schematics: A 1:1 electrical recreation of the original Nintendo (OEM) logic.

• 3D-Printable Housing: Custom shell files for those who want a modern look or need to replace a missing cover.

• Modern PCB Standards: Recent community updates have even moved the project toward a 4-layer PCB design, ensuring that data and clock lines are perfectly synchronized to prevent the crashes seen in early third-party clones.

The RDRAM Challenge

Despite the open-source nature of the board, one major obstacle remains: the RDRAM chips. The Nintendo 64 uses a specific type of Rambus memory that has been out of production for years.

“The reason this is cheap for me is because I snagged a specific lot of old stock chips for $1.50 each,” Stooksbury explained during a community update. While the board files are free, builders still need to source the actual memory chips—often “harvested” from broken consoles or found in obscure “new old stock” warehouses.

Why This Matters

For us at Everything64, this project represents a massive win for digital preservation.

• Repairability: Broken OEM Paks can now be diagnosed and fixed using the released schematics.

• Price Ceiling: By providing a DIY alternative, the project helps prevent the price of original Expansion Paks from skyrocketing toward $100+.

• Custom Modding: The open-source files allow other developers to integrate the 4MB of RAM directly into custom portable N64 builds or “all-in-one” motherboard redesigns.

The long-term challenge for this project however could be the dwindling supply of original RDRAM chips, which have been out of production for over 20 years. Because the N64 cannot use modern memory, the Expansion Paks are forced to rely on “New Old Stock” or salvaged parts from broken consoles, which may eventually lead to rising costs and a finite number of available modules. But we will see what the future brings. 

How to Get One

The files are live on GitHub for anyone with soldering skills to build their own. Commercial versions based on his work are available on specialist sites like Consoles4You and classicgamestore.