Panasonic KX-FPC135 Service Manual page 179

5. [Film End Sensor (PS501)]
As the amount of the film decreases, the revolving speed of the rolled film becomes faster. When the film is used up, it comes
off from the paper roll. The amount of the remaining film is measured by the revolving speed. When the film stops turning
around, the sensor detects the film end.
The rotary encoder rotates slowly when the ink film is full (when printing), as shown in the diagram below. It rotates faster when
it is near its end. Sensor PS501 converts the rotation of the rotary encoder into pulses and the amount of the remaining ink film
is then calculated internally by the ASIC (IC501) and stored into memory. Then an error message such as "FILM EMPTY" or
"FILM NEAR EMPTY" appears on the LCD display.
6. [Motor Position Sensor (Switch)]
This sensor is a detection switch for recording the position of the CAM.
Digital Board
Signal (IC501-138 pin)
Home position
Other
179
Low level
High level
KX-FPC135 / KX-FPC141