Epson Stylus Photo785EPX, Service Manual

Page: 51 / 192

EPSON Stylus PHOTO 895/785EPX/915/825 Revision B
Operating Principles Electrical Circuit Operating Principles 51
2.2.2.2 Printhead Driver Circuit
The printhead driver circuit consists of the following two components:
„
Common driver IC (IC12:E09A14RA) directly attached to the C408/C498
MAIN board.
„
Nozzle selector IC on the head board.
The common driver (IC12:E09A14RA) generates a reference drive waveform
according to the output signals from the C408/C498 MAIN board. The reference drive
waveform is amplified by the transistors Q2 and Q3 and then transferred to the nozzle
selector IC on the head board. Print data is converted to serial data by the CPU (IC2)
and then sent to the nozzle selector IC on the head board. Based on the serial data, the
nozzle selector IC determines the nozzles to be actuated. The selected nozzles are
driven by the drive waveforms produced by the common driver. See Figure 2-20.
"Printhead Driver Circuit" for the printhead driver circuit block diagram.
†
Head common driver circuit
The reference head drive waveform is produced in the common driver
(IC12:E09A12RA) based on the following 12 signal lines output from the CPU
(IC12); A0-A4, CLK1, CLK2, RST, FLOOR, DATA, DCLK, and E.
By the DATA signal output from the CPU (IC9), the original data for the head
drive waveform is written in the memory in the IC12. The addresses for the written
data are determined by the A0 - A4 signals, and, of among, data used to determine
the waveform angles is selected. Then, setting the selected data, producing
trapezoid waveform value, and canceling the data are performed by the rising
edges of the CLK1 and CLK2 signals.
†
Head nozzle selector circuit
Printing data is converted into serial data by the CPU (IC2). Then the converted
data is allocated to the six rows, the number of the head nozzle rows, to be
transferred to the nozzle selector through the six signal lines (HS01 to HS06). Data
transmission from the CPU (IC2) to the nozzle selector synchronizes with the LAT
signal and SCK clock signal. Referring to the transferred data, nozzles to be
activated are selected, and the PZTs of the selected nozzles are driven by the drive
waveform output from the head common driver.
Figure 2-20. Printhead Driver Circuit
HWA0
HWA1
HWA2
HWA3
HWA4
HWCLK
HWCLK
HWFLR
HWRST
HWSDA
HWSCL
HWSLA
HCH
HLAT
CRAI0
CRAI1
SWC0
SWC1
HSO1
HSO2
HSO3
HSO4
HSO5
HSO6
HSOCM
HNCHG
HSOCLK
ANO
A0
A1
A2
A3
A4
CLK1
CLK2
FLOOR
RST
DATA
DCLK
E
VCC
NPNB
FB
PNPB
COB
COA
SI1
SI2
SI3
SI4
SI5
SI6
SP
NCHG
SCK
THM
CH
LAT
ENA
ENB
VHV
COM
COM
COM
COM
CN8
CN9
F1
IC2 CPU
E01A22C*
IC12
Common
Driver IC
Nozzle Selector
IC
Head Drive
Pulse
VHV