OKIDATA Microline 395, Service Handbook

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%2.1.08 Alarm Circuits
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/ribbon 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 (HDE ALM, HDO ALM, LF
COM or RBN COM) will be sent to the fault alarm circuit. The fault alarm circuit generates the ALM signal
(high) 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 rises. If the head temperature reaches approximately 115
degrees Celsius, a head overheat condition (ALARM 1) is generated.
When ALARM 1 is detected, bi-directional printing stops. Uni-directional printing continues.
If the printhead temperature continues to rise, ALARM 2 is generated. All printing stops.
Printing resumes when the head temperature falls below the ALARM 1 level.
Cover Open Alarm Circuit
When the front access cover is opened, the COVOPEN-N signal is sent to the Slave MPU from the cover
interlock microswitch. The Slave MPU relays the switch status to the Master MPU. The Master MPU will
halt printing at the completion of the current line and light the ALARM Lamp.
ML395 ( 96-02-03 )