Canon CP660 Service Manual page 220

CHAPTER 6 FIXING SYSTEM
b. Open Circuit in the Fixing Heater (E004)
At the start of temperature control, the printer unit drives the upper fixing heater and
the lower fixing heater, one at a time to check the FXSTS signal for an open circuit in the
fixing heaters.
The fixing assembly error detection circuit detects AC current flowing through the fix-
ing heater. If AC current is absent, the M-CPU on the DC controller PCB will assume the
condition as an open circuit in the fixing heater, stopping the drive to the fixing heater and
communicating the fact to the printer board*
The AC current to the upper/lower fixing heater is checked in reference to the voltage
induced at T101. The voltage occurring at T101 is monitored by pin No. 10 of IC102. If the
upper/lower fixing heater has an open circuit or if the upper thermal switch opens, AC cur-
rent stops flowing and the output of pin No. 13 of IC102 goes '1'. As a result, the output
of pin No. 14 of IC102 will be '1', and the fixing heater status detection signal (FXSTS)
will go '0'.
If AC current is flowing, on the other hand, the FXSTS signal alternates between '1'
and '0' at specific intervals, allowing the M-CPU to use the FXSTS signal to detect an
open circuit in the fixing heater.
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* Reader controller PCB (when making prints with the reader unit installed).
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COPYRIGHT © 1999 CANON INC.
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as a fault in the fixing assembly.
CANON 660/2100 REV.0 FEB. 1999 PRINTED IN JAPAN (IMPRIME AU JAPON)