System Reset Circuit; Printhead Driver Circuit - Epson LQ-2170 Service Manual

Operating Principles

2.3.2 System Reset Circuit

Control circuits IC1 and IC2 are initialized when a RESET signal (LOW level) is output from port 1 (VOUT)
of IC10. IC10 monitors the +5 V line on port 3, and resets under the following conditions:
1. When the power supply is turned on, a RESET signal is output. RESET is canceled when the
+5 V line goes up to 4.2 V, and then 100 ms passes.
2. When the +5 V line goes below +4.2 V, a RESET signal is output. RESET is canceled when the
+5 V line goes back up to 4.2 V and then 100 ms passes.

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 R50 and
R51 to determine the printhead drive pulse width. Using the monitored voltage, the CPU converts the
voltage to a digital value and decides the printhead drive pulse width, and then transports the data to the gate
array via CPU port 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 110° C (228° F) ,
printing is stopped.
2-24
IC2
+5V
RESET
R47
1K
IC10
PST5920
+5V
VOUT 1
MRES
2
VCC
3
GND
4
C16
0.1U
Figure 2-32 Reset Circuit
(v)
5
4
100ms
3
2
1
RESET
Power On
VOUT (RESET)
Figure 2-33 Reset Signal Output Timing
Print Head
Printhead Drive Transistor Q5~Q13, Q14~22
Printhead Drive Signal
69 76~89 91~93
28
37
Address
Gate
CPU
Data Line
Array
21
44
32 19
79 78
Figure 2-34 Printhead Drive Circuit
E05813YA
61
IC1 TPM96C041AF
23 RESET
100ms
RESET
VCC (+5V line)
+35V +35V
HTMP
+
C9
R49
R50
+35V
74
73
R51
ZD1
+35V
C19
LQ-2170 Service Manual
Rev.A