Toshiba e-STUDIO520 Service Manual page 302

6) Temperature detection circuit
Thermistors are elements whose resistance decreases as they detect a higher temperature. Thus,
the input voltage to the main-CPU is changed and the main-CPU judges whether this change is
abnormal or not. If one of these thermistors is broken, the control circuit judges that the temperature
of the fuser roller or the pressure roller is extremely low. Then the circuit keeps turning the IH coil on.
As a result of this, the fuser roller temperature rises, and this may activate the thermostats, a safety
protection element. To prevent this problem in advance, the main-CPU works to detect the wire
breaking of each thermistor.
These thermistors also check the temperature of the fuser roller or the pressure roller regularly to
prevent them from excessive heating caused by a circuit abnormality or a thermistor abnormality. If
the temperature of these rollers has exceeded a specified level, the thermistors automatically turn
the power of the equipment OFF.
Fuser roller
center thermistor
Fuser roller
rear thermistor
Fuser roller
front thermistor
Pressure roller
thermistor
e-STUDIO520/600/720/850 FUSER UNIT
+5.1VC
MTH--1A
+5.1VC
STH--1A
+5.1VC
ETH--1A
+5.1VC
PTH--1A
Fig.14-8
14 - 12
IC58
Main CPU
THMCH-1
1
0
IC24
Analog
multiplexer
March 2005 © TOSHIBA TEC