Specifications

11.4.2 Overheat Protection
IC121 and Q110 form an overheat protection circuit. When the fusing lamp is
controlled within the normal range, pin 7 of IC121 stays LOW; therefore,
Q110 stays on, allowing PC402 to operate. If the hot roller temperature
reaches 240
o
C, the resistance of the thermistor becomes too low. At that
time, pin 7 of IC121 becomes HIGH, turning off Q110 and stopping PC402.
At the same time "E53" lights on the operation panel and the power relay
(RA401) turns off.
Even if the thermistor overheat protection fails, a thermofuse is installed in
series with the fusing lamp. If the thermofuse temperature reaches 169
o
C,
the thermofuse opens, removing power from the fusing lamp.
1 December 1990
2-75