Kyocera Mita DC-2060, Руководство по обслуживанию

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1AH
2-3-12
(1) Abnormally high fixing temperature detection circuit
CPU
(IC32)
I/O
(IC27)
1
IC35B
H ALARM
TR11
IC47D
R149
R150
18 67
CN10-3
CN11-7 FTH
H REM
S
S
S G
S G
+
–
Figure 2-3-13 Abnormally high fixing temperature detection circuit
CPU (IC32) of the main PCB monitor the fixing temperature by voltage of the fixing unit
thermistor (FTH) input at pin 1 (A/D input) and controls the fixing heater on/off that it
output the fixing heater control signal (H REM) to the composite PCB via pin 67 of the I/
O control LSI (IC27). At the same time, this voltage is input to the inverted input terminal
of the comparator (IC35B) on the Abnormally high fixing temperature detection circuit .
Reference voltage (abnormally high fixing temperature voltage) 5 V DC set by resistors
(R149, R150) is applied to the non-inverted input terminal of IC35B. When voltage of
the fixing unit thermistor (FTH) is exceeded by the voltage at the inverting-input, the
output of IC35B goes low.
This signal is input at the base of the transistor (TR11) as the abnormally high fixing
temperature detecting signal (H ALARM). When the input goes low, transistor turns off,
regardless the fixing heater control signal level at pin 67 of the I/O control LSI (IC27),
the corrector voltage goes high, IC47D output goes high. The fixing heater control signal
(H REM) of the composite PCB goes high, the fixing heater turns off.
The H ALARM signal is input pin 18 of the I/O control LSI (IC27), and is detected from
CPU (IC32). CPU determines abnormally high fixing temperature if this H ALARM signal
continues more than 4 s, and display service call “C640”.