Oki ML520, ML521 manual Principles of Operation Head Overheat Alarm Processing

Page: 41

Service Guide ML520/521

Chapter 2 Principles of Operation

Head Overheat Alarm Processing

If the printhead temperature exceeds 110 degrees Celsius, the printer will switch to uni-directional print. If the temperature exceeds 118 degrees Celsius, printing will stop. Once the printhead cools, printing will resume.

Two thermistors are used to monitor the printhead temperature. One is contained in the printhead. The other is in the printhead driver.

A thermistor in the printhead prevents over-heating of the coil during periods of continuous bi-directional printing. If the temperature of the coil exceeds the pre-determined limits, the control circuit detects the thermistor signal (TSD).

Another thermistor monitors the temperature of the printhead driver. If the temperature of the driver exceeds the pre-determined limits, the control circuit detects the thermistor signal (TSD).

The voltage of the TSD signal is monitored at the MPU A/D port to control the pass number and print method (uni-directional / bi-directional) at each of seven levels.

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