If you have the remote, try this. I'm not sure it will work, but it is worth a shot. Make sure the power is off:
Press DISP, 5, VOL+, PWR ON
or
DISP, 5, PWR ON
If it works you'll know it. Be sure to record any values before you change them.
To navigate you press 1 to go back to the previous item in the menu, 4 to go forward, 3 to adjust the value up and 6 to adjust the value down. To save, you need to press mute and then immediately press enter.
You're looking for the VPOS and VSIZ menu items, probably.
Good luck.