Panasonic KX-FP101AL Service Manual page 149

5. [Paper top Sensor (PS502)]
When the recording paper is loaded on the print head, the shelter plate shuts the sensor light, and the phototransistor becomes
OFF. The input signal of IC501-152 pin becomes a high level. Usually, the shelter plate is lifted, the phototransistor becomes
ON, and the input signal of IC501-152 pin becomes a low level.
Set recording paper
No recording paper
6. [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.
Phototransistor Signal (IC501-152 pin)
OFF High level
ON Low level
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KX-FP101AL