Mattel service centers used the MTE 201 test cartridge as a diagnostic cartridge for the original Intellivision. It tests the hand controllers, sound, color and each chip on the motherboard. I’m told it’s pretty much impossible to decipher the test routine unless you have the Intellivision Service Manual.
One sold back in October for $181.09. There’s also repo boxes floating around for these, as the original never came in a box.