User manual

95.08.23.11.30
Color LaserWriter 12/600 PS Basics & Theory 1–117
• When the THI signals are compared after changing the sensitivity of
the thermistor (see note 3 below) from the high range to the low
range, there is almost no difference recognized (the wiring for the
thermistor is broken).
Notes:
1 If a failure occurs in the fuser heater, do not turn on the printer
power switch for about 30 minutes. Even if the power switch is
turned on during this time period, the CPU determines the fuser
heater failure has occurred and the fuser heater will not be turned on
to prevent it from overheating. Discharging jumper JP102 on the DC
controller board will reset this circuit.
2 The off-timer circuit on the DC controller board can measure the
lapse of time after the power is turned off. The measured time is
used for release of fuser assembly errors and for tempera-
ture/humidity sensing.
While the power is turned on, the CPU (IC101) sets the off-timer
charge signal (
/TCCHG) to be output to IC102 to “L” to charge
C106. After the power is turned off, C106 begins to discharge.
When the power is turned on again, the CPU detects the voltage of
C106 with the off-timer sense signal (
OFTMR), sets the TCCHG
signal to “L,” and charges C106 to the specified voltage. Then the
off-timer discharge signal (
TCDIS) is set to “H” and C106 is forcibly
discharged to the voltage level measured at the time of power-on,
and the required time is measured. Based on this measured time, the
time during which the power was turned off is calculated.
3 The sensitivity of the thermistor differs between its high and low
temperature ranges. In order to increase the detection accuracy in
either range, the CPU in the DC controller uses the thermistor sensi-
tivity select signal (
THSEL) to switch the thermistor sensitivity
between the mode in which the detection accuracy is higher at low
temperatures and that in which it is higher at high temperatures.
When the
THSEL signal goes “H,” the thermistor is put in the low
temperature detection mode, and when “L,” in the high temperature
detection mode.
DC Controller Board
/TCCHG
TCDIS
OFTMR
CPU
IC101
5V
Off-Timer Circuit
IC102
C106