Most of the time when you see a repair video of a Game Boy it’ll be demonstrated with a cartridge inserted and booting up into the game, but does this actually mean that the system is truely fully functional? There can still be more intermittent faults, dodgy buttons, or even something like a defective link port — all of which can be much harder to detect than firing up a copy of Tetris. This is where the GB Test Lab cartridge by [Marcel Pflug] of the Game Boy Museum comes into play.

With the freely available ROM put on an EverDrive or similar flash cartridge, you can test a whole range of functions of the original Game Boy (DMG-01), most of them autonomously and some with some user input.

This is similar to the test cartridge that Nintendo themselves used in the form of the DMG-AGING-01, which validated the basic functionality of the handheld. Since then a myriad of test cartridges have been created by the homebrew community, but not all try to test quite literally everything possible. In the case of the GB Test Lab this includes the typical like CPU, RAM, interrupts, etc., but also key bounce time, intermittent connectivity and playing a game of Pong between two GBs connected by link cable as well as using the GB Printer.

Results are saved per GB and persisted if the flash cartridge has battery backup or similar. Overall it seems quite comprehensive and something that’s worth giving a shot if you’re the kind of person who owns one or more GBs. Perhaps the neatest part of this ROM is that it also contains a built-in reference for all the components and other useful details, including how to interpret results and symptoms.