Super Star Soldier

Super Star Soldier
Developer: Inter State Software Publishers: NEC (US), Hudson Soft (JP) Platform: TurboGrafx-16 Released in JP: July 6, 1990 Released in US: 1991 This game has a hidden sound test. This game has a hidden level select.

Hidden menu

At the title screen, press Left, II, Up, II, Right, II, Down, II, Left, I, Up, I, Right, I, Down, I, then press I + II eight times followed by I + Select eight times for a hidden menu containing a Sound Test and difficulty setting.

(Source: GameFAQs (AWing Pilot))

Expanded Hidden Menu

Hold Run+Select before powering on the console, then enter the above code to add a screen size toggle and level select to the menu.