Forcing 400 to use external screen

[JPE]

I auired a 400 with a broken screen.  When it boots, it is using the 
external as a second and I cant get to the menus. Is there a way to 
force it to use the external screen or cause it to use the external as 
the main?

TIA

JP
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"If you think it's not a game, you already lost" - J.P. Edmund