Ricoh C211 Service Manual page 433

9-3. Temperature Ascent Detection of Thermal Head/Power Supply: SS950
A thermistor located on the thermal head and a thermal guard located on the power
supply board are used for thermal protection. This is to prevent the temperature of the
thermal head and the power supply
ing a solid image.
Thermal head detecting temp.
Thermal head return temp.
Power supply detecting temp.
board from overheating when continuously
process-
54°c
50"C
85°C
When the thermistor is open, a detection signal is applied.
d=
5V
Thermistor
Thermal head
Thermal Quard I
CN404 +5V
CN702-7
-
-13m
!
CN404
,
CN702-6 -llfi
u
Thermal Head
Drive PCB
CN4011
I
P
-ll,_J
I
__!!!-l
Psu
Master Processing
Control PCB
CN402
)
-11
Main Board
The thermal head temperature detection signal is applied if CN404-I 1 becomes greater
than 3.13 volts (Thermal head detecting temp--- 54"C).
Note:
The thermal head temperature detection signal is applied if the thermistor is open.
The thermal head temperature return signal is applied when CN404-I 1 becomes 2.98
volts (Thermal head return temp --- 50"C).
The thermal guard detection signal is applied if CN401 -11 is O volt (Power supply detect-
ing
temp---
85°C).
The thermal guard temperature return signal is applied when CN401 -11 becomes 5 volts.
When the temperature ascent signal is applied CN402-I 1 goes HIGH.
When the temperature ascent signal is applied during master processing, master
processing continues until completion. The machine stops after the master making
process is finished.
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