Alarm Circuits - OKIDATA Pacemark 3410 Service Manual

Page: 21
Service Guide PM3410
Chapter 2 Principles of Operation

2.1.08 Alarm Circuits

Fault Alarm Circuit (in Power Supply Unit)
This protective circuit turns off the power supply when a fault occurs in the printhead, line feed, or bail
motor drive circuits, thus preventing secondary component failure.
To accomplish this, the circuit monitors the overdrive signal of each drive circuit. If the duration of any
drive circuit exceeds a predetermined length of time, the appropriate signal (EVN COM, ODD COM, LF
COM or BM COM) will be sent to the fault alarm circuit. The fault alarm circuit generates the ALM signal
which causes the power supply to turn all DC power OFF.
Printhead Overheat Alarm Circuit
In order to protect the printhead coils, this circuit monitors the printhead temperature by using a thermistor
contained in the printhead. The CPU senses this circuit every time a line is printed.
When printing, the printhead temperature will increase. If the head temperature reaches approximately
115° Celsius, a head overheat ALARM 1 is generated. When ALARM 1 is detected by the MPU, the
printer will begin unidirectional printing. If the printhead temperature increases to 125° Celsius, ALARM 2
is generated and printing is halted until the head temperature decreases. When the head temperature
returns below the ALARM 1 threshold, printing is resumed.
Cover Open Alarm Circuit
When the front access cover is opened, the CVOPEN-N signal is sent to the MPU from the cover interlock
microswitch. The MPU will halt printing immediately and light the ALARM Lamp.
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