Hold Select and enter 68K as initials on the high score screen.
Plug a TurboTap with a controller into port two. Select two
player mode and pause game play. Replace the TurboTap and
with a single controller. Resume game play with overlapping
from last game location:
Press Left, Right, Down, Up, then hold Select and press Left
at the "Game Over" screen.
Hold I + II and press Run at the title screen.