Electrical Circuit Operating Principles

The Stylus 1500 contains the following circuit boards:

□ C172 MAIN Board (main control circuit board)

□ C172 PSB/PSE Board (power supply circuit board). This is the same board used in the Stylus Color printer.

□ C172 PNL (control panel board)

In addition to the circuit boards above, part of the printhead drive circuit is built on a separate circuit board installed in the carriage unit; the printhead is attached directly to this board. The figure below shows a block diagram of the electrical circuitry.

Electric Circuit Diagrams Epson
Figure 2-18. Electrical Circuit Block Diagram 2.3.1 Power Supply Circuit Operating Principles

The power supply circuit for this printer is provided either by the C172 PSB board (120 VAC) or by the C172 PSE board (220-240 VAC). Both boards are identical in design and function, except for the components in the primary circuit that accommodate the specified input voltage. The input voltages and applications of output voltages are summarized in the table below.

Table 2-7. DC Voltage Distribution

Voltage

Application

+42 VDC

□ Motor drive (carriage and paper feed) □ Printhead (through the drive voltage generation circuit)

+5 VDC

□ C172 MAIN board logic circuit □ Sensors (home position, paper end, no ink cartridge, head thermistor) □ C172 PNL control panel board, head nozzle selector

The figure below shows a block diagram of the power supply circuit (C172 PSB/PSE). The power switch is in a secondary circuit that allows the CPU to remain active for a minimum of 20 seconds after the printer is turned off. This allows the printhead to return to the capping position. The CPU, which is mounted on the C172 MAIN Board, monitors the PSC (power on/off) signal. If this signal goes LOW, the CPU resets each device after performing the head-capping sequence.

This board also employs an RCC (Ringing Choke Converter) switching system. The AC voltage is first input to the filter circuit for higher harmonics absorption and is then input to the rectification and smoothing circuit, converting it into DC voltage. This DC voltage is input to the switching circuit. Along with the switching operation on the primary side, +42 VDC is generated after passing through the +42 V line voltage detection circuit. This +42 VDC output level is stabilized and is also input to the +5 VDC generation circuit to produce a stable +5 VDC.

Figure 2-19. Power Supply Circuit Diagram

+5 VDC Line Overvoltage Protection Circuit

The output voltage level of the +5 V line is monitored by a Zener diode (ZD53). If the voltage level exceeds +9 V, the status is fed back to the primary switching circuit through photocoupler PC1 to cut the +42 V until the power is turned on again.

+5 VDC Line Overcurrent / Overvoltage Control Circuit

The output current is monitored by a +5 VDC generation switching control IC (IC51), which also monitors the output voltage. This information is input to the internal comparator and cuts the +5 VDC when the voltage or current becomes abnormal.

+42 VDC Line Overvoltage Protection Circuit

The output level is monitored by two Zener diodes (ZD52 and ZD87). If the voltage level exceeds +48 V, photocoupler PC1 is activated to stop the primary switching circuit operation.

+42 VDC Line Drop Protection Circuit

The output level of the +42 VDC line is monitored by a detection circuit consisting of Zener diodes (ZD51 and ZD81 to ZD86). This circuit feeds back the output voltage level status through photocoupler PC1 to the primary switching circuit, to control the on/off time of the switching transistor for constant output voltage.

+42 VDC Line Overcurrent Protection Circuit

The output current is monitored by transistors Q81 and Q82. This circuit feeds back the output voltage level status through photocoupler PC1 to the primary switching circuit to stop the circuit's operation.

2.3.2 Main Control Circuit Operating Principles

The main control circuit for this printer is the C172 MAIN Board, which is controlled by a 16-bit TMP96C061AF CPU (IC1) running at 24.57 MHz. A 4M DRAM (CAS method) on this board is controlled by the CPU itself. The CPU manages the Type-B interface control.

Gate array E05B16 (IC2) manages the printhead driver control, external Centronics parallel I/F, control panel, and control motors.

This board is also equipped with a 93C46 EEPROM (IC11) to store parameters such as the printer mechanism control parameter, default setting parameters, and the special counter value used for printhead (ink management) protection.

The NJU6355E timer IC (IC10) counts each time the printer is cleaned and keeps track of how long the printer is not used, thereby allowing the printer to be cleaned only when necessary.

Reset IC for Logic

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