Canon CP660, Service Manual

Page: 216 / 407

COPYRIGHT © 1999 CANON INC. CANON 660/2100 REV.0 FEB. 1999 PRINTED IN JAPAN (IMPRIME AU JAPON)
C. Protecting the Fixing Assembly
The printer unit is equipped with the following three types of protective mechanisms
to prevent malfunction of the fixing heater:
• The M-CPU monitors the voltage of the upper fixing roller temperature detection sig-
nal (FXTHU) and the lower fixing roller temperature detection signal (FXTHL). If
either or both incur an error, the M-CPU will identify the condition as a fixing heater
fault, and will communicate the fact to the printer board*
1
to cut off the power to the
heaters.
• If the fixing temperature increases abnormally and, as a result, either or both upper
and lower thermistor (THU, THL) readings exceed about 230°C, the safety circuit will
cut off the power to the heaters regardless of the output of the M-CPU. At the same
time, the M-CPU identifies the condition as a power supply fault, and communicates
the fact to the printer board1 by way of the D-CPU.
• If the fixing temperature increases abnormally and, as a result, the temperature of
either or both upper and lower thermal switch exceeds about 240°C, the upper/lower
thermal switch will turn off to cut off the power to the fixing heaters.
*
1
Reader controller PCB (when making prints with the reader unit installed).
D. Detecting a Fault in the Fixing Assembly
A fault in the fixing assembly is checked by the following three:
1. M-CPU on the DC controller PCB
2. Fixing heater safety circuit (in the power supply circuit)
3. Fixing assembly error detection circuit (in the power supply circuit)
Details follow.
1. M-PCU on the DC Controller PCB
If the fixing assembly is abnormally heated or it fails to reach a specific temperature,
the M-CUP uses the D-CPU to stop the operation of the fixing heater, and cut the relay
(RL101) to shut off the power to the fixing heater.
The DC controller then communicates the fault in the fixing heater to the printer
board*
1
.
Specifically, the M-PCU detects a fault in the fixing heater under any of the following
conditions:
a. A fixing assembly error is stored in the error memory capacitor (C259) on the DC con-
troller PCB at time of power-on. (error low temperature E003 or error high tempera-
ture E001)
b. The increases in temperature are monitored every 20°C from 20°C to when the stand-
by temperature is attained after the fixing heater is driven; the time required is com-
pared against the reference time, and the time required is longer than the reference
time.
c. The fixing assembly temperature drops below 120°C after it has reached the target
level. (error low temperature E003)
d. The fixing temperature reaches about 230°C or more during standby or during copy-
ing. (error high temperature E001; Note 1)
CHAPTER 6 FIXING SYSTEM
6-4
Note:
To reset the printer unit after a fixing heater error has been stored in the error memo-
ry capacitor (C259), turn it off and then on after leaving it alone for 30 min or more.
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