Olivetti ECR 8220, Service Manual

Page: 57 / 122

3-14. PRINTER CIRCUIT
Thermal Head
The thermal head of the printer consists of heat elements, and head drivers to drive the heat
elements.
Serial printing data input from the DAT IN pin is transferred to the shift register synchronously with
the CLK signal, then stored in the latch register with the timing of the LATCH signal.
Inputting the head activation signal activates heat elements in accordance with the printing data
stored in the latch register.
Each 144-dot block for LTPC235 are printed.
Sensor
This printer has Head-up sensor and Paper-end sensor.
Both signals normally outputs Low, but it out puts High when Head-up or Paper-end.
This High signal goes through Nor-gate and changed Low, then it is input into CPU (U1).
Excitation Sequence
As shown in Table 3-14-1, the printer feeds paper in the normal direction when the motor is
excited in the order of step 1, step 2, step 3, step 4 step 1, step 2, ….by inputting the voltage
signals in Figure 3-14-1.
Figure 3-14-1. Input Voltage Signals for the Sample Drive Circuit
Table 3-14-1. Excitation Sequence
Service Manual 57