Horizontal Sync Generator Mechanism; Laser Chip Thermistor Malfunction; Beam Detect Pulse - Canon LBP-CX Series Service Manual

condition in the the thermistor, it cuts power to the
laser heater, and sets the READY signal (RDY)
FALSE. The video controller thus knows that a mal-
function has occurred, and responds by sending a
STATUS REQUEST command to the DC controller
via the COMMAND/STATUS signal (SC). Upon
receipt of this command, the DC controller sends a
status report to the external device (via SC) noting
that a malfunction has occurred in the laser tempera-
ture control circuit.
Thermistor
Detection
malfunction
Open
At power ON, the temperature
circuit
does not reach the specified value
within about 10 minutes.
During printing, the temperature
drops under the lower limit
(34°C).
Short The temperature exceeds the
circuit · upper limit (50°C).
Table 3-6 Laser chip thermistor malfunction
Notes:
IC208 begins detecting lower limit temperature
(34°C) once the laser chip temperature reaches the
specified value. This prevents the printer from
being disabled for printing (RDY is FALSE) when
the power is switched ON.
If the thermistor is short-circuited, IC208 starts
detecting the upper limit temperature and printing
is disabled.
Printing is disabled when the READY signal
goes false. Once this signal goes FALSE, and the
printer is switched OFF, temperature adjustments
will not be made on the laser chip for about 10
minutes. This allows plenty of time for the laser to
cool and prevents overheating.
After power is switched back ON, microcom-
puter IC208 will not check for a thermistor malfunc-
tion for about 10 minutes, but even though heated by
by the laser heater, this is not enough time to damage
the laser chip.
d. Stationary mirror and horizontal sync generator
(a part of the the DC controller)
Beam-to-drum
Photo-
sensitive
drum
LO
Scanner motor
Figure 3-53 Horizontal sync generator mechanism
+24V
Optic
~
P0201 , - ; - - - - - - - ,
+5V -5V
J203
R259
Figure 3-54 Beam detect pulse (IBD)
The horizontal sync generator mechanism is
shown in Figure 3-53. The circuit for the horizontal
sync generator is shown in Figure 3-54.
The laser beam strikes the stationary mirror after
reflecting off the scanning mirror and passing through
the focusing lens. Reflecting off the stationary mirror
once every scan, the laser beam, which is transmitted
by an optic fiber, illuminates photodiode PD201,
which causes IC212 to produce a pulse (IBD).
IC212 is a comparator: when PD201 is illumina-
ted, IC2 l 2-2 is more positive than IC2 l 2-3, which
sets IC212-6 HIGH; when PD201 is not illuminated,
IC212-2 is more negative than IC212-3, which sets
IC212-6 LOW.
!--!
2- 4 µsec
1
.Sms
IBD
Figure 3-55 Beam detect pulse (IBD)
3-42
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©
BY CANON INC. CANON LBP-CX SERIES REV.2 JULY 1985 PRINTED IN JAPAN (IMPRIME AU JAPONJ