Interface(I/F) Circuit; Head Temperature Detector Circuit; Head Drive Voltage Measurement Circuit; Rear And Front Paper End Detector Circuit - Epson LQ-670 Service Manual

Chapter 2 Operating Principles

2.2.2.9 Interface(I/F) Circuit

The interface of this printer consists of gate array, parallel I/F connector and optional type-B I/F connector.
Input of parallel I/F is pulled up by 3.3K resistance and goes to 10 resistance, which is serially
connected to the port DIN0-7 of the gate array. The output is done from the port in the gate array via
LS06. The input signal of Type-B I/F; /CMREQ, /WRRDY, /RDREQ and output signal INH are connected
to the gate array via 100 resistance which is connected serially. The input signals are pulled up by 1K
resistance, and are connected to the gate array serially. The output signals are output from the gate array
via serially connected 100 resistance.

2.2.2.10 Head Temperature Detector Circuit

This printer has the thermistor in the print head, which monitors the head temperature in order to prevent
the head coil from being degraded or worn out by the continuous high duty printing.
The head temperature signal HTMP measures the resistance value of the thermistor as voltage in the A/D
converter of the CPU port AN0 by sending the current to the 1.21K 1% resistor, which is connected
serially to the thermistor.

2.2.2.11 Head Drive Voltage Measurement Circuit

The head voltage drive circuit consists of the partial pressure resistance and CPU. Drive voltage is
pressured 1/9 by resistance and is input to the port of CPU as VREF signal, and is measured by A/D
converter in the CPU inside.

2.2.2.12 Rear and Front Paper End Detector Circuit

The PE detector circuit of this printer consists of PE detectors(each at front and rear) by micro-switch and
CPU. Each detector opens when there is a paper, and shorts when there is no paper.

2.2.2.13 Paper Width Detector Circuit

The paper width detector circuit consists of the paper width detector on the mask holder and CPU. The
paper width detector uses photoelectric transfer method and detects top and bottom of the paper and
paper width. The signal of the paper width detector is input to the port P52 of CPU, and is detected its
level by the A/D converter. When there is a paper, the paper width detector shorts and opens when there
is no paper.

2.2.2.14 Carriage Home Position (HP) Detector Circuit

The HP detector circuit of this printer consists of photoelectric transfer method type detector and CPU.
The HP detector detects the carriage home position. The output of the HP detector is input to the port P53
of CPU and is detected its level by the A/D converter which is built inside. When the carriage is in the
home position, the detector opens, and shorts when the carriage is out of home position.

2.2.2.15 Release Lever Detector Circuit

The release lever detector circuit consists of the release lever detector micro switch and gate array. The
release lever detector signal(RELEASE) is detected in the port of the gate array. The detector opens at
the friction mode and shorts at the tractor mode.

2.2.2.16 Adjust Lever Detector Circuit

The adjust lever detector circuit of this printer consists of the micro switch detector and CPU. The detector
shorts, and printing speed becomes copy mode when the adjust level is more than 2 levels. The detector
opens, and printing speed becomes normal when the adjust level is less than 1 level.
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Rev. A