Canon NP-70 Service Manual page 96

NP-70
3-59
3.4-10 HEATER CONTROL CIRCUIT — "ZERO~ROSS" (ALL COPIERS EXCEPT 100VAC)
+24VDC O
The "Zero-Cross" Heater Control Circuit operates to maintain the temperature in the Heater
Assembly at 180 ± 3°C, but its operation differs from the previously explained heater control
circuit. These differences are as follows:
a) In machines using the "Zero-Cross" circuit, all heater elements are controlled. In the
100VAC circuit, one element operates continuously while the other two elements are con-
trolled.
b) The "Zero-Cross" circuit is divided into two control portions —one for activating the
heaters in a continuous, but low-level, manner and one for activating the heaters at a high
level when the temperature drops.
c) The "Zero-Cross" circuit uses astep-down transformer to convert the high A. C. line
voltage for controlling operations of the circuit.
Fig. 3-21 shows the "Zero-Cross" circuit and its associated components.
TH1
-~
OVDCp
COMP.
NET.
~--
P
FULL WAVE
1/
ZERO-
CROSS
P/0
TP231
E
T
1/4
ZERO-
CROSS
HALF
WAVE
D231
T201
P/0
TP231
_,
LINE A O C
I M ~ B
HEATER
ASS'Y
Q236
"ZEROLORSS" HEATER CON. CKT. CARD
Fig. 3-21 `Zero-Cross" Con. Ckt. &Associated Components
_J
O
LINE AC
1) OPERATION —GENERAL
The "Zero-Cross" heater control circuit begins operation as soon as the copier is turned ON.
The general operation is as follows:
a) As the copier is turned ON, line voltage is applied to transformer T201 and 24VAC is
applied to bridge-rectifier D231.
© CANON INC.
Second Printing-June, 1974