Epson FX-980 - Impact Printer, Service Manual

Page: 33 / 72

FX-980 Revision A
Operating Principles Control Circuit 33
2.3.3 Printhead Driver Circuit
The standard voltage for the A/D converter is made in ZD1 and input to
CPU port 78. Based on this standard voltage, the A/D converter in the
CPU operates. Port 74 monitors the +35 V line between R70 and R71 to
determine the printhead driver pulse width. Using the monitored
voltage, the CPU converts the voltage to a digital value and decides the
printhead driver pulse width, and then transports the data to the gate
array via CPU ports 15 and 19. Based on the monitored voltage, the
CPU decides the printing interval. Port 73 monitors the printhead
temperature to protect the printhead. If the temperature exceeds 107
°
C
(225 ° F), printing is stopped.
Figure 2-5. Printhead Drive Circuit
2.3.4 CR Motor Driver Circuit
The CR motor driver circuit is shown below.
Figure 2-6. CR Motor Driver Circuit
The carriage motor driver circuit controls the CR motor, using an
open-loop, constant drive arrangement. 2-2 and 1-2 phases excite the
motor. One step of the 2-2 phase switching system corresponds to 2
steps of the 1-2 phase switching system. Ports 1, 8, 11, and 18 of the
SLA7024M are used to change the excitation phase, depending on the
selected print mode. Table 2-2 on the following page describes the
motor driver modes.
The SLA7024M (IC9) CR motor driver circuit detects and regulates the
amount of current flowing in the carriage motor coil. The current flowing
through the coil varies, depending on the speed of the CR motor. The
CPU sets the amount of current via the Address / Data line. Signals are
sent via ports 3 (RFA) and 14 (RFB) to the SLA7024M. The SLA7024M
sets the coil current, depending on the CR speed.
G a t e
A r r a y
C 4 2
Z D 1
+ 3 5 V
7 8 7 9
7 4
7 3
R 7 1
R 7 0
+ 3 5 V
R 7 2
A d d r e s s
D a t a L i n e
P r i n t h e a d D r i v e T r a n s i s t o r Q 2 - Q 1 9
P r i n t h e a d
H T M P
+
C 2
+ 3 5 V + 3 5 V
3 2
1 5
C P U
P r i n t h e a d D r i v e S i g n a l
3 1 1 9
I C 2 C P U
6
5 / I N A
/ I N - A
1 7
1 6 / I N B
/ I N - B
I C 9 S L A 2 0 2 4 M
8
1
1 8
1 1
C N 1 1
1
3
2
4
A
/ A
B
/ B
6 8
P G 0 0
P G 0 1
P G 0 2
P G 0 3
6 7
5
6