GE marquette MAC 1100, Servicing Instructions

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Marquette Hellige GmbH MAC 1100/1200 V 1.1 Page
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2.3.9 Printhead control
The printhead controller takes on the complete control of the 216-mm thermal
printhead with a line width of 200 mm.
The output rate to the printhead is 1000 /sec. The resolution in the Y-direction is
8 dot/mm, in the X- time axis up to 40 dots/mm.
Thermal Printhead Dot Control:
The MPC821 prepares a complete dot column and sends it to the FIFO. A complex
PLD reads out a complete column of the FIFO and generates the digital control
signals for the printhead, which are shifted in series.
The duration of heating a dot column is defined through the pulse width of the PWM
Signal HEAT that is generated from the complex PLD too.
In addition, the duration of heating a dot column is influenced by the thermal
printhead monitoring.
Thermal Printhead Temperature Monitoring:
The thermal printhead temperature monitoring measures the temperature of the
thermistor, located on the printhead. A constant current source effects a
temperature-dependent voltage drop.
If a printhead temperature of 55°C is exceeded, the signal REC_OVHEAT_ is
activated and the heating of the printhead is prevented by disabling the signal
STROBE.
Only when the printhead temperature drops below 50°C is the signal
REC_OVHEAT_ disabled and the heating via the signal STROBE re-enabled.
In addition, a continuous reduction of the heating duration occurs with increasing
printhead temperature, resulting in a regular typeface throughout the entire
temperature range.
2.3.10 Motor control
Paper transportation for the speeds 5mm/s, 25mm/s and 50mm/s is driven by a
stepping motor. The stepping motor is controlled by an integrated stepping motor
driver circuit. The current for the motor is adjusted by the sense resistors of the
stepping motor driver.
For the speed 5mm/s, the motor current is reduced, triggered by the signal
LOW_SPEED.
The motor speed is controlled by the frequency of the signal RECTMR_STEP, which
is generated by the timer unit of the MPC821.
The driver circuit is enabled by the signal REC_MOTEN, the driver is powered from
+22,5V.