Schiller AT-102, Service Handbook

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2.5
Article Number 2. 540 028
SCHILLER AG 2002
AT-102 Service Handbook
Section 2
Functional Overview
MK 18 - 1 Main Board
Printer Timing
Strobe generation is controlled by the CPU when one complete pixel line of data is ready to
be written. Pulse length of STRB1 and STRB2 (each of which controls half of the pixel
array) depends from TPH temperature and so form the pulse width of the TPHT signal.
Paper Mark
The pulsed paper mark signal from the printer is fed to a comparator. A detected papermark
sets PMARK at the output of comparator (U44), to logic 0.
Power On Reset
The Power on reset circuit controls the master reset of the CPU. This circuit has two
functions as follows:
To provide a delay on initial switch-on to ensure that the power supply is fully
stabilized and give the 200ms reset time required by the 68332 processor.
To disable the unit if the +5V rail drops below +4.75V.
Stepper Motor Controller
The printer stepper motor controller sets the speed of the printer motor with a clock
frequency dictated by the master CPU.
The purpose of the stepper motor controller circuit is to ensure that the motor speed
requested by the microprocessor is achieved and maintained.
ECG Isolated Power Supplies
DC/DC converter circuits produce all the isolated power voltages required by the ECG
Amplifier circuit.
The -2.0Vi and the 2Vi isolated reference voltages are generated from the -5Vi supply.
Note: When taking measurements always ensure that the isolated ground is used for
reference.