B. Fixing Control Circuit - Canon LBP-1000 Service Manual

B. Fixing Control Circuit

1. Fixing temperature control
The fixing film unit contains a plate-shaped fixing heater to heat the fixing film.
The fixing heater temperature is detected by the thermistor (TH701) on the fixing heater.
When the surface temperature of the fixing heater rises, the resistance value of TH701 decreas-
es, and the voltage of the FIXING HEATER TEMPERATURE DETECTION signal (FSRTH) decreas-
es.
The CPU (IC402) on the engine controller controls the FIXING HEATER DRIVE signal (FSRDO)
based on the voltage of the FSRTH signal in order to bring the fixing heater temperature to the
specified value.
No power is supplied to the fixing heater when the printer is in the STANDBY mode.
When a print instruction command is input from the video controller, the CPU starts the ini-
tial temperature control of the fixing heater.
Fuse
SW201
(FU201)
+3.3V
SSR301
Q302
Thermal fuse (FU1131) J301-1
Thermistor
(TH701)
At this time, the CPU monitors the FSRTH signal and sets the THERMISTOR SWITCHING sig-
nal (THCHG) to "H" when the fixing heater temperature is low (Initial temperature control) and
to "L" when the temperature is high (Print temperature control) in order to improve the FSRTH
Engine controller PCB
Relay
(RL301)
J303-2 J303-1
Fixing film unit
J301-2
Fixing heater (H701)
Figure 2-2-5
Fixing heater safety circuit
+24V
+3.3V
Q304
Q305
+3.3V
FSRTH
IC503
10
-
13
11
+
CHAPTER 2
FSRDO
35
RLYD
20
IC402
CPU
FSRTH
40
+3.3V
THCHG
43
Q303
2 - 9