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Check for unused graphics. Clock graphics are stored before the Super Mario Bros. 2 ROM and can be viewed in a hex editor.
Add the 5 hidden images and the methods in which they are seen.
Game & Watch: Super Mario Bros. is a special Game & Watch unit made to celebrate the 35th Anniversary of Super Mario Bros., containing said game, The Lost Levels, and a Mario-themed version of Ball (a concept Nintendo had already done in G&W form as Mario the Juggler, itself notable for being the last game of the original G&W series). Strangely enough, the actualGame & Watch Super Mario Bros. is nowhere to be seen.
Much to everyone's (dull) surprise, it was only available through March 31, 2021, though at least this one having a limited run is more understandable than the othertwo Mario games released around the same time considering its more niche demographic.
Another special Game & Watch unit, this one themed around the Legend of Zelda series, was released on November 12, 2021 for that series' 35th Anniversary.
A simple factory test menu is present that was used during the hardware's production to check if the handheld works as intended. To access the menu, power off the console by pressing the POWER button for 5 seconds while it's plugged in to any AC power outlet. Then hold Up + B, press POWER, then before the Mario Clock appears, release Up and B, and press GAME + PAUSE/SET.
After hitting this button combination, the system will cycle through the following tests:
Power (Eject / Insert / Current Battery Power + user confirmation)
Buttons (D-Pad / A / B / Face buttons)
Sound (Volume 0 / 5)
LCD (White / Black / Red / Green / Blue / Shade horizontal / Shade vertical)
If the test results are OK, hold B to power off. Upon booting back, the system will have its time reset to 12:00 PM.
The same menu is present in Game & Watch: The Legend of Zelda and accessed the same way, the only change being the ability to test the additional buttons the console has.
Eject the USB-C cable.
Insert the USB-C cable.
Check current: active charging.
Check current: charging off, screen on.
Check current: charger off and standby. Tests the standby option and has you press POWER again after the screen went black.
Button test, D-Pad Up.
Button test, D-Pad Up + Left.
Button test, D-Pad Left.
Button test, D-Pad Left + Down.
Button test, D-Pad Down.
Button test, D-Pad Down + Right.
Button test, D-Pad Right.
Button test, D-Pad Right + Up.
Button test, A button.
Button test, B button.
Button test, GAME button.
Button test, TIME button.
Button test, PAUSE/SET button.
Button test, D-Pad Left + A.
RTC test, during the calculation process.
RTC test that passed.
RTC test that failed, triggered by halting execution with debugger while testing is in progress; cannot continue past this point.
Speaker test starts on volume level 3. You can press GAME to continue to the next test.
Speaker test, on the lowest volume.
Speaker test, on the highest volume.
Before the LCD test.
LCD test, white screen.
LCD test, black screen.
LCD test, red screen.
LCD test, green screen.
LCD test, blue screen.
LCD test, vertical shade.
LCD test, horizontal shade. After this screen, you can press GAME to continue.
You can also adjust the brightness using D-Pad Up and Down on any of the LCD test screens.
Test result, this one passed.
Test result, taken before shutdown.
A few miscellaneous strings are present in the internal flash.