Oki Microline 390, Руководство по обслуживанию, Страница: 37 / 174

Printhead overheat alarm circuit
In order to protect the printhead coils, this circuit monitors the printhead temperature by
using the thermistor which is built into the printhead.
If heavy-duty printing is performed continuously for a long time, the printhead temperature
increases.
The timing and types of alarms and printing actions with respect to printhead temperature
are as shown in the following.
Printing Mode
2nd Alarm
Bit IMAGE
3 PASS print P.H. stop
(See Note
Uni-direction print P.H. stop
3rd Alarm Others
3 PASS print Normal print
Uni-direction print Normal print
Note 1.
Note 4. 3 PASS Print,
tensseconds
afterprinthead
temperature has
Temp
exceeded 90°C for the
first time.
For the period during
temperature is higher
than 130%
For
several
tens seconds
afterprinthead
temperature fallen
below 130%
Each line is printed out
being divided into
three cycles --with 8
dots for each cycle.
Note 5. When approximately20 seconds has
halting, 3
PASS printing
in starts.
Alarm detection is performed as follows:
When the temperature in the printhead increases, the resistance of the thermistor decreases
and the voltage at the comparator
positive input decreases to invert the comparator
output, causing the HEAD TEMP signal to be sent to the motor control
3.1.9 Paper end detection circuit
When no paper is installed or a end of paper condition exists, the photo-sensor on the control
board is turned off changing the PAPER END signal to a low level. This signal is fed to pin 55 of the
motor control
which causes the printing operation to halt and the ALARM indicator to
illuminate.
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