(2)
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
1stAlarm
2nd Alarm
Bit IMAGE
3 PASS print
P.H. stop
(See Note
5.)
Others(characters) Uni-direction print P.H. stop
3rd Alarm
Others
3 PASS print
Normal print
Uni-direction print Normal print
Note 1.
lstA/arm:
Note2
2ndAlarm:
Note3.
3rdAlarm:
Note 4.
3 PASS Print,
Forseveral
tensseconds
afterprinthead
temperature has
Temp
exceeded 90°C for the
[“C)
first time.
For the period during
whichprinthead
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
elapsedafter
halting, 3 PASS printing
in
uni-direction
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 (97) positive input decreases to invert the comparator
output, causing the HEAD TEMP signal to be sent to the motor control
LSI.
3.1.9 Paper end detection circuit
When no paper is installed or a end of paper condition exists, the photo-sensor
(PE)
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
LSI
(Qll),
which causes the printing operation to halt and the ALARM indicator to
illuminate.
3-10
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