Toshiba e-STUDIO2500c Service Manual page 334

[ 2-7 ] Temperature detection circuit
The therrmistor is a device whose resistance varies according to the detected temperature, and the
thermopile is a device whose output voltage varies according to the detected temperature. The ASIC
detects voltages output from these devices, and judges whether the operation of the fuser unit is nor-
mal or abnormal from the changes in voltages.
If one of the thermistors and thermopiles is broken, the control circuit judges that the temperature of the
fuser belt or pressure roller is extremely low and keeps turning the heater lamps ON. As a result, the
temperature of the fuser belt or pressure roller rises, and possibly activates the thermostat which is a
safety protection device. To prevent this in advance, the ASIC works to detect whether each thermistor
and thermopile is broken or not.
Also, the the control circuit constantly checks the temperature of the heat roller and the pressure roller
to prevent them from excessive heating by circuit abnormality or thermistor abnormality, and automati-
cally shuts OFF the power when one of these temperatures exceeds the specified temperature.
Fuser belt
front thermistor
Fuser belt
center thermopile
Fuser belt
rear thermopile
Pressure roller
center thermistor
Pressure roller
rear thermistor
e-STUDIO2500c/3500c/3510c FUSER UNIT / PAPER EXIT SECTION
+5.1VB
BHETH
SG
+5.1VB
BHCTH
SG
+5.1VB
BHSTH
SG
+5.1VB
PHCTH
SG
+5.1VB
PHETH
SG
Fig. 15-5
15 - 10
IC72
A/D
converter
IC41
ASIC
May 2006 © TOSHIBA TEC