Epson Stylus COLOR 1520 Service Manual page 67

‰Common driver circuit for the black head
Gate array E05B33 (IC6) sends serial data to the head nozzle selection circuit on the head to select
nozzles to activate. Then the data is transferred to the common driver on the control board to drive all
piezos that are corresponding to each nozzle. The operating principles for the black head is as follows:
„Nozzle selection circuit
Nozzles for the black head are divided into 2 rows with 64 nozzles on each, and 2 deferent types
of nozzle selection signal (BAHDATA and BBHDATA) are sent in serial data to the corresponding
row. Clock signal (BHCLK) is composed of the pulses from #1 to #64. The nozzles to be activated
is determined by the nozzle selection signal synchronized with the clock signal by the latch signal
(BHLAT). However, the numbers used for the pulses and corresponding nozzles are not the same.
„Common driver circuit
The common voltage (VH) is established to correspond to each of the black printhead
characteristics. This value is stored in advance in the EEPROM when the printer power is off. At
power on, the value is stored in the RAM. The gate array E05B33 (IC6) refers to the value for the
common voltage when outputting the serial data SBDATA as the voltage control signals to the
common driver circuit. The serial data transmission control signals (SCLK, SSTB and SCLR) are
used for this operation. The thermistor controls the common voltage by outputting the signals to
compensate for changes in ink viscosity.
Rev. A
Figure 2-25. Black Data Transmission Timing
Operating Principles
2-25