Panasonic KX-FP81BX Service Manual page 153

3. [Cover Open/Film End SW (SW501)]
When the operation panel cover is closed and a film is set, the SW becomes ON, and the input signal of IC501-43 pin (Digital)
becomes a low level. When the cover is opened, the SW becomes OFF, and the input signal of IC501-43 pin (Digital) becomes
a high level.
Cover open or no film
Cover closed and set a film
4. [Hook Switch (SW101)]
When the handset is lifted, the switch turns ON, and the signal at pin 35 of IC501 becomes low.
When the handset is returned, the switch turns OFF, and the signal at pin 35 of IC501 becomes high.
ON-Hook
OFF-Hook
Digital Board
Photo transistor Signal (IC501-43 pin)
OFF High level
ON Low level
Digital Board
SW Signal (IC501-35 pin)
OFF High level
ON Low level
153
KX-FP81BX / KX-FP81CX / KX-FP82CX