Ricoh FT5540, Service Manual

Page: 93 / 734

6.7 TONER OVERFLOW SENSOR CIRCUIT
31 August 1989
The toner overflow sensor signals the CPU when the toner collection bottle is full.
A tiny tuning fork is used as the sensing element for the toner overflow sensor. This tuning
fork is a damping element in a multivibrator circuit. As long as there is nothing in contact with
the tuning fork, the oscillating frequency of the circuit stays LOW and the transistor stays off.
When toner presses against the tuning fork, the resistance of the piezoelectric elements that
are in contact with the tuning fork changes and the oscillating frequency increases. The
frequency detection circuit passes the higher frequency signal to the rectifier which activates
the switching transistor. The transistor sends a LOW signal to CN103-7 on the main board.
When the CPU receives this LOW signal, it signals the copier to stop, lights the Used Toner
Bottle indicator, and blinks the Service Call indicator. Also, a message instructing the
customer to call for service is displayed on the guidance display.
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