Fixing Roller Heater Control; Thermistor Malfunction; Fixing Roller Temperature - Canon LBP-CX Series Service Manual

Temperature
(oC)
WAIT
I
STBY :
I
I
I
I
INTR-PRINT-LSTR STBY
Auxiliary (manual) feed
180
170
- - - - - - 1 - - - - -i- - - _,......_ ....... """"' ........ _.......,_,_-.,._ - - - - - - - - --
1 I
- - - - - - l.. - - - -
L -
I
I I \
I
I \
160 ...c>~~~-
- - - - - - - -
--1-\-\- -
.1- .........
-~
............................ ,.,
I \ \
I \ \
I I \ \
I \
- - - L - - - - - - - - - - - - - - -
---\-'r- ----- -----
: l
I
1
140
Power
switch on
F" •
I
OK If H1
I
t
f
1xmg temp.
burned Malfunction
out (ROY is FALSE)
Figure 3-45 Fixing roller temperature
(1)
Introduction
The fixing roller heater temperature control
circuit keeps the temperature of the fixing roller
even, and changes the temperature according to the
printer printing sequence. During STBY, the tempera-
ture is maintained at 160°C. During INTR, PRINT
and LSTR, the temperature is maintained at 170°C
for cassette feed and 180° C for auxiliary (manual)
feed.
(2) Operation
·1~
LC
Temperature
~ ~
ACP1
FSRTH sense
Figure 3-46 Fixing roller heater control
Microcomputer IC208 reads the FIXING ROL-
LER TEMPERATURE signal (FSRTH) from thermis-
tor THI, which contacts the upper surface of the
fixing roller when ACPl from the zero-cross gen-
erator (See Fig. 3-42) is TRUE. IC208 detects the
surface temperature of the fixing roller and checks
whether the temperature has reached the specified
level. If it is lower, IC208 sends a TRUE FIXING
ROLLER HEATER DRIVE command (FSRD) to
photocoupler PClOl on the AC driver. PClOl turns
on transistor 'QlOl. When QIOl turns ON, a gate
voltage is applied to gate G of triac QI and QI turns
ON. Power is supplied to fixing roller heater Hl.
(3) Thermistor malfunction
Microcomputer IC208 self-diagnoses any thermis-
tor malfunction detected. To prevent damage to the
printer, power to fixing roller heater Hl is cut, and
the READY signal (RDY) sets FALSE. This informs
the external device that a malfunction has occurred.
The external device responds by sending a STATUS
REQUEST to the DC controller over the COMMAND
/STATUS signal (SC). When the DC controller re-
ceives this command, it sends a FIXING ASSY MAL-
FUNCTION status report back to the external device
via the SC signal.
Printing is disabled at the time the READY signal
goes FALSE.
Thermistor
Detection
malfunction
Open circuit At power ON or PAUSE command
input, the temperature does not
reach a specified value (160°C)
after about 70 seconds.
During printing, the temperature
drops below the lower limit
(140°C).
Short circuit
The temperature exceeds the
upper limit (230°C) ..
Table 3-5 Thermistor malfunction
Notes:
IC208 begins detecting the lower limit tempera-
ture after the upper fixing roller temperature once
reaches the specified value.
If the thermistor is short-circuited and the power
is switched ON, IC208 assumes the fixing roller
heater is at the upper limit temperature. The
printer is disabled from printing.
If a breakdown of the thermistor is detected by
microprocessor IC208, the microprocessor sends
a fixing assembly breakdown signal (FSERL) to
the buffer IC (IC203), via 1/0 port IC227.
COPYRIGHT
©
BY CANON lllC. CANON LBP-CX SERIES REY.2 JULY 1985 PRINTED IN JAPAN (IMPRIME AU JAPONJ
3-37