Black Printing - Epson Stylus 1500 Service Manual

Operating Principles

Black Printing

Common Driver Circuit
The common voltage (VH) corresponds to characteristics of the specific black printhead installed.
This value is stored in advance in the EEPROM on the C172 MAIN board by the host computer.
(See Head Data Writing Operation in Chapter 4.) Gate array E05B16 (IC2) refers to this value when it
outputs parallel data for voltage control signals (BHV0 - BHV5) to the common driver circuit. The
common voltage is then established at one of 64 levels, with 26 V as the center driver voltage value.
The CPU monitors the signal from the thermistor in the black printhead driver circuit to
compensate for changes in ink viscosity based on the temperature surrounding the printhead. The
CPU then adjusts the VH value and the interval (Thd) between the first and second common pulses
in one dot.
Head Driver Circuit
Gate array E05B16 (IC2) converts print data into serial data and outputs it from port CHSO (pin 39)
to the color head driver circuit. Head driver SED6100D then latches the head data when gate array
E05B16 outputs the BHLAT signal, and the latched data becomes 64-bit parallel data for the black
head. One bit corresponds to each nozzle.
When data transfer and nozzle selection are complete, gate array E05B16 outputs the signal all
nozzles ON (NCHG), the black head charge pulse (BH1C/2C), and the black head discharge pulse
(BH1/2D) to the common driver circuit. This circuit then generates the trapezoidal pulse and
applies it to the printhead as a common driver pulse. After this, the nozzle selected by the head
data is activated to eject the ink.
BHSO
# 1
B HC L K
BHLAT
NCHG
COM
BH1/2C
BH1/2D
Figure 2-27. Normal Dot Data Transmission Timing
2-24
# 6 4
V H
Tdh
Rev. A