Canon SELPHY CP770 Service Manual page 55

(8) Confirm that the center density of the printed image is between the lower limit density and the higher limit
density as shown. If the center density is between them, this is the end of the adjustment. If it is not, go to
step (9) and the following steps.
Higher limit density
(9) While printing an arbitrary image, measure the voltage of the test point while printing is in progress.
When the printed image is denser than the higher limit density, adjust the control volume so that the test
point voltage is decreased by 0.3V lower than the specified voltage. When the printed image is less dense
than the lower limit density, adjust the control volume so that the test point voltage is increased by 0.3V
higher than the specified voltage.
(10) Repeat steps (6) to (8). If the printed image still does not satisfy the specification, increase or decrease the
voltage by assumption and repeat steps (6) to (8) again.
Center density Lower limit density
4