Fuser Heater Lamps Control Circuit - Kyocera Mita FS-C5016N - Color LED Printer Service Manual

FS-C5016N

(1) Fuser heater lamps control circuit

Power supply PWB
AC input
TRA1
PC1
Fuser
heater
lamp 1
thermisotor 2
The ON/OFF action of the fuser heater lamp 1 and 2 are controlled by the fuser heater lamp 1 and 2 lighting ON signals
(HEAT1ON, HEAT2ON) output from the No.35 and 36 pin of ASIC (U13) of the engine controller PWB. When the
HEAT1ON and HEAT2ON signals reach the H level, the photocouplers (PC1, PC2) and triacs (TRA1, TRA2) turn on
because the transistors (Q47, Q50) turn on and then the AC voltage is loaded to the fuser heater lamps. The HEAT1ON
and HEAT2ON signals turn ON/OFF the photocouplers (PC1, PC2) and triacs (TRA1, TRA2) being synchronized with the
zero cross signal (ZCROSS) that is detected by the zero cross signal detection circuit on the power supply PWB. The
ZCROSS signal detects the zero cross point (0V) where the AC power source changes between positive/negative
domains and it is input to the No.39 pin of the ASIC (U13) of the engine/high voltage PWB. Since the ON/OFF operation of
the photocouplers (PC1, PC2) and triacs (TRA1, TRA2) are performed at the zero cross point (0V), it can avoid the sharp
change of current and restrain noises generated from the AC power source.The fuser thermistor detection voltages (TH1,
TH2) are input to the micro controller (U8) and branched to input to the comparator (U1-1, U1-2). The comparator (U1-1,
U1-2) compares the TH1 and TH2 signals voltage with the unusually high temperature voltage. If the voltage TH1 and TH2
signals voltage are higher than unusually high temperature voltage, the output level is L. For the HEAT1ON and HEAT2ON
signals, the circuit that forcibly turns off the fuser heater lamps by the hardware-based method and forcibly makes the
HEAT1ON and HEAT2ON signals to L level regardless of controls by ASIC (U13) is provided fuser heater lamp ON signals
(HEAT1ON, HEAT2ON).
This circuit is provided for the purpose of fail safe, it usually monitors the unusual high temperature in the software system
by the input voltage of the TH1 and TH2 signals that are input to the No.3 and 4 pin of micro controller (U8), therefore, the
circuit operates the control to turn off the fuser heater lamps before the mentioned circuit is activated and stops the
machine, and then indicates the error code 6020 or 6120 that shows the fuser high temperature failure according to the
self diagnosis function.
2-3-4
Zero
cross
signal
detection
circuit
TRA2
PC2
Fuser
thermisotor 1
Fuser
heater
lamp 2
Fuser
Engine controller PWB
Pulse
HEAT1DR
Fuser heater lamp 1
3
2
Q47
HEAT2DR
1
Fuser abnormal
+5V1
Q50
3
Fuser heater lamp 2
2 ON circuit
1
Fuser abnormal
temparature
+5V1
detection
circuit
(U1-2)
Figure 2-3-3
39
ZCROSS
ON circuit
35
HEAT1ON
48
temparature
H1HTEMP
detection
circuit
(U1-1)
36
HEAT2ON
49
H2HTEMP
Micro
controller
3
TH1
4
TH2
ASIC
(U13)
(U8)