To enter Service Mode, hold down the Menu button while rapidly pressing the up and down arrows, starting with up and alternating between them.
When you start holding down Menu, you see:
When you have done the up-down thing correctly, it changes to:
At that point you can stop holding down Menu and stop pressing Up and Down, and you’ll see Adjustment on the screen, as in step 2 of the calibration instructions.
Here are instructions for calibrating the sensors:
Remove both cassettes.
1: First enter service mode
2: Adjustment will show up on printer screen.
3: Scroll down one time until Sensor check shows up
4: Select set and SN01-SN10 will appear
5: Scroll down all the way until Auto Adjustment appears
6: Select the set button and the printer will go through the adjustment.
Turn off printer put cassettes back in and check quality.