Okidata ML321 Turbo, ML320 Turbo Service Manual

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Service Guide ML320/321Turbo

Chapter 0 About This Manual

ML320 Turbo // ML321 Turbo

Dot Matrix Printers

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copy of the OKIDATA Service Training Manual.

09/17/97

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Table of Contents Page

Service Guide ML320/321Turbo

0 About This Manual

Front Cover 1

1 Configuration

1.1. Standard Printer Configuration 2

1.2 Options 3

2 Operation Description

....2.1.1 Summary 4

....2.1.2 Microprocessor and the Peripheral Circuit 5

....2.1.3 Initialization 6

....2.1.4 Parallel Interface Control 7

....2.1.5 Print Control 8

....2.1.6 SP/LF Motor Control 9

....2.1.7 Operation Panel 10

....2.1.8 Alarm Circuit 11

....2.1.9 Power Supply Circuit 12

2.2 Mechanical Operation 13

....2.2.2 Spacing Operation (See Figure 2-4.) 14

....2.2.3 Head Gap Adjusting (See Figure 2-5.) 15

....2.2.4 Ribbon Drive (See Figure 2-6.) 16

....2.2.5 Paper Feed Operation 17

....2.2.6 Paper Detection Mechanism (See Figure 2-15.) 18

....2.2.7 Automatic Sheet Feed 19

....2.2.8 Paper Park Function (Continuous sheet paper) 20

3 Parts Replacement

3. ASSEMBLY/DISASSEMBLY 21

3.1 Precautions for Parts Replacement 22

3.2 Service Tools 23

3.3 Disassembly/Reassembly Procedure 24

....3.3.1 Printhead 25

....3.3.2 Ribbon Protector 26

....3.3.3 Pull-up Roller Assy 27

....3.3.4 Upper Cover, Access and Sheet Guide Assy 28

....3.3.5 Gear Case Assy 29

....3.3.6 PC Connector 30

....3.3.7 Space Motor, Guide Roller Assy 31

....3.3.8 Space Rack 32

....3.3.9 Carriage Cable 33

....3.3.10 Backup Roller Holder Assy 34

....3.3.11 Platen Assy 35

....3.3.12 Driver Board (SDDV) 36

....3.3.13 LF Motor 37

....3.3.14 Operation Panel PCB (LEOP) 38

Table of Contents Page

....3.3.15 Control/Power Supply Board (SDCT) 39

....3.3.16 Transformer Assy 40

....3.3.17 Change Lever and Gears 41

....3.3.18 Carriage Shaft 42

....3.3.19 Paper Pan 43

....3.3.20 Rear Tractor Assy 44

....3.3.21 Rear Pressure Assy 45

....3.3.22 Switch Lever 46

4 Adjustments

4. ADJUSTMENT 47

5 Periodical Maintenance

5.1 Cleaning 48

5.2 Lubrication 49

6 Troubleshooting

6.1 Items to Check Before Repair 50

6.2 Troubleshooting Table 51

6.3 Lamp Display 52

6.4 Connection Circuit Check for Printhead and SP/LF Motor 53

6.5 Troubleshooting Flow Chart 54

A Centronics Parallel Interface

A. PCB LAYOUT 55

B Parts Listing

Parts Listing 56 Figure 11-1 Upper Cover Assy 57 Figure 11-2 Printer General Assy 58 Figure 11-3 Printer Unit 59 Figure 11-4 Carriage Assy 60 Figure 11-5 Option Spare Parts 61

C Software Diagnostics and Adjustments

RS-232C SERIAL INTERFACE BOARD 62

2. OPERATION DESCRIPTION 63

....2.2.1 Operation at power on 64

....2.2.2. RS-232C interface 65

2.3 Communication Procedure Flowchart 66

3. TROUBLESHOOTING FLOWCHART 67

3.3 Local Test 68

Service Guide ML320/321Turbo

1.1. Standard Printer Configuration

This printer consists of the following assemblies:

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Chapter 1 Configuration

1.2 Options

(1) Cut sheet feeder unit (CSF) Single-bin CSF

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Service Guide ML320/321Turbo

Chapter 1 Configuration

(2) Pull-tractor assy

(3) Bottom push tractor unit

(4) Roll paper stand (Narrow only)

(5) Serial I/F

- RS-232C

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Service Guide ML320/321Turbo

Chapter 2 Operation Description

2.1.1 Summary

Fig. 2-1 shows the block diagram of the printer. The control board is made up of the microprocessors, peripheral circuits, drive circuits, sensors and

interface connectors. The power to the control board is supplied by the power board through the connector cord. The power to other electrical parts is also distributed through the connectors within the control board.

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Service Guide ML320/321Turbo

Chapter 2 Operation Description

2.1.2 Microprocessor and the Peripheral Circuit

(1) Microprocessor (Q7: 67X640) This processor is a CMOS single-chip computer with integrated peripheral device functions and a 16-bit

MPU core, all OKI original architecture. The processor has a 20-bit address bus and a 16-bit data bus. It is capable of accessing up to 1M word program memory and 1M bytes of data memory. The following characteristics are also provided:

- Built-in type data memory of 512 bytes

- 8-bit 4-channel A/D converter x 1

- 16-bit automatic reload timer x 2

- 8-bit serial port x 2

- 8-bit parallel port 3 3 (bitwise I/O specification available) And others. The function of this microprocessor is to provide a central mechanism for the entire printer by executing

the control program through the LSI and driver circuits. (2) Program ROM This is a 256 x 16 bits (4M bit) [MAX] EPROM with the control program for the printer stored. The MPU

executes instructions under this program. The program ROM is assigned to the program memory area of the MPU and is fetched by the PSEN

signal of the MPU. The following shows the operation of the memory access.

(3) RAM (MSM51C464A-80RS) The RAM is CMOS dynamic RAM with (64K x 4-bit) x 2 configuration, and used as buffers (such as

receiving buffer, printing buffer, DLL buffer and working buffer). The following shows examples of the memory access operation.

(4) EEPROM The EEPROM is a CMOS serial I/O type memory which is capable of electrically erasing and writing 1,024

bits. The EEPROM contains menu data. The following shows the memory access operation.

(5) LSI This LSI detects and controls the SP motor speeds by monitoring the two-phase sensor signals obtained

from the DC motors and modifying the excitation phases as appropriate. This LSI is connected in multiplex to the MPU.

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Service Guide ML320/321Turbo

Chapter 2 Operation Description

2.1.3 Initialization

This printer is initialized when the power is turned on or when the I-PRIME-N signal is input from the host side via the parallel interface.

For the initialize operation, the RST-N signal is first output from the reset circuit to reset the MPUs and LSIs. When resetting ends, the program starts and the LSIs are reset by MPU via LSIRST-N. Reset operation by I-PRIME starts the program to initialize, but does not reset the MPU. The program sets the mode of the LSI including the MPU, checks the memories (ROMs and RAMs), then carries out carriage homing, and determines the LF motor phase.

Finally, the program establishes the interface signals (P-I/F: ACK-P signal sending, and S-I/F: BUSY-N signal off) and lights the SELECT lamp. When the ready state is set, the host is informed that the printer is ready to receive data.

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Service Guide ML320/321Turbo

Chapter 2 Operation Description

2.1.4 Parallel Interface Control

The parallel data input from the host to the interfaced LSI is latched to its internal register at the falling edge of the STROBE-N signal.

At the same time, the LSI sets the BUSY signal to the high level to inform the host that the data is being processed, and outputs the RXD signal to inform the MPU of data reception. The data is read upon receiving the RD-N signal from the MPU.

When the data processing ends, the BUSY signal is set to off and the ACK-N signal in sent to request the next data. When reception is impossible because the buffer is full, the BUSY signal is sent to stop data transmission.

Service Guide ML320/321Turbo

Chapter 2 Operation Description

2.1.5 Print Control

Print data is transmitted as parallel data (HEAD1-HEAD9) from the LSI to the print head. The LSI generates the print timing and drive time.

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Print Compensation Control

The print compensation methods are shown below: (a) Voltage compensation (b) Temperature compensation (c) Pin stroke compensation

(See 2.1.8 "Alarm Circuit."

)

(d) Simultaneous Compensation of the number of impact pins The MPU is provided with the compensation table for each pin to compensate as necessary.

Number of impact pins Drive time Short < ------ >Long

(e) Print mode compensation According to the thickness of the printing medium, the print mode is compensated as shown in the table

below

Few < ----- > Many

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Service Guide ML320/321Turbo

Chapter 2 Operation Description

2.1.6 SP/LF Motor Control

(1) Space motor control The SP motor driver (HA13412) drives the three-phase brushless motor based on the phase signal (SPU,

SPV and SPW) and the speed instruction data from the LSI. The MPU can identify the current speed of the space motor by measuring through the LSI the pulse length of the output (øA, øB) of the slit encoder included in the space motor.

By comparing the target speed for each print mode with the actual current speed to change the speed instruction data, the motor speed is increased or decreased to maintain the specified speed for each print mode.

(2) Encoder disk In the operation of the spacing motor, the PHASE-A and PHASE-B signals are generated when the encoder disk interrupts the photo sensor. The LSI divides these edge pulse signals in accordance with the print pitch, and sends the IPT signal to provide dot-on timing and carriage position detection timing.

(3) LF motor control The LF motor driver (MTD2005F) drives the LF motor in two-phase or 1-2 phase bipolar, based on the phase changeover data and the output current data from the LSI. The data from the LSI is processed by a specific register contained in the LF motor driver to measure the overdrive time and to change the phase.

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Service Guide ML320/321Turbo

Chapter 2 Operation Description

2.1.7 Operation Panel

The clock synchronization OPCLK signal of the LSI is used to input the switch data and output the LED data through the operation panel control LSI (IC1: BU5148S).

A 2-byte (15 bits + 1 even parity bit) command signal (OPTXD) is transmitted to the LSI(BU5148S) in synchronization with the OPCLK signal. The LSI decodes this command and when it is found to be legal, returns a 2-byte command response back to the LSI which includes data on Switch information, LED status, receive command ACK/NAK and 1 odd parity bit. Any transmission errors found cause the command to be reissued after the transmission of the OPCLR-N signal.

ote: From the illustration above, you can see that the command and the command response are output at the same time. This is because the bit 0 to bit 3 the OPRXD signal are fixed so that the response can be returned before decoding the command.

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Service Guide ML320/321Turbo

Chapter 2 Operation Description

2.1.8 Alarm Circuit

(1) Head drive time alarm circuit This circuit monitors the drive time using the HDALM signal interlocked with the overdrive signal of each

drive circuit. If the drive time of any drive circuit exceeds the specified time, the drive fault alarm circuit sends an

ALARM-N signal to turn on the SCR (SO). This causes the secondary coil (40V) of the transformer to short-circuit, causing an overcurrent to flow

through the primary coil and open the AC fuse (transformer assy). (2) Alarm processing when DC power is low. + 40V is converted into the POWLEV signal (0V to +5V) by R28 and R29 and input into the A/D port of the

MPU to control the drive time and the print speed (pass number) of the head.

(a) Head drive time

The head drive time is lengthened to compensate for the amount of voltage drop by monitoring the POWLEV signal once every 500 m sec. to control and maintain the impact necessary for each printing pin at the fixed value.

(b) Print Speed

(3) Head overheat alarm The voltage of the output TSD signal of the thermistors, one of which is in the printhead and the other in

the printhead driver, is monitored by the CPU/AD port to control the voltage

- When the temperature is between a°C and 119°C, the mode switches sequentially to higher level. When the temperature falls below ß°C, the mode switches to lower level.

- When the temperature exceeds 119°C, printing stops.

- When temperature gradient is steep, the higher mode is specified directly.

Service Guide ML320/321Turbo

Chapter 2 Operation Description

2.1.9 Power Supply Circuit

This power supply circuit supplies the +5VDC, +8VDC, +40VDC, 10VAC.

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The uses of output voltages and signals are described below.

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Service Guide ML320/321Turbo

Chapter 2 Operation Description

2.2 Mechanical Operation

2.2.1 Printhead Mechanism and Operation (See Figure 2-2 below). The printhead is a spring charged 9-pin driving head using a permanent magnet. It is attached to the

carriage, which moves parallel to the platen. Electrically, this unit is connected to the control circuits through the control board.

(1) The printhead configuration The printhead is composed of the following parts: (a) Wire guide (b) Spring assembly (Wire, Armature, Spring, Yoke, Spacer) (c) Magnet assembly (Magnet, Core, Coil, Yoke) (d) Printed circuit board (e) Fin (2) Printhead Operation (See Figure 2-3 below). (a) When the printhead is idle, the armature is attracted by a permanent magnet and the spring fixing the

armature is compressed. The print wires fixed to each armature are thus concealed under the wire guide. (b) When a signal for a character to be printed is detected, a current flows through the coil. When the coil

is activated, the magnetic flux (caused by the permanent magnet between the armature and the core) is canceled to eliminate the attracting force. The armature is driven in the direction of the platen by the force of the armature spring. The print wire fixed to the armature protrudes from the tip of the wire guide, strikes the paper through the ribbon and prints a dot on the paper.

(c) After the character has been printed, the armature is magnetically attracted again and the print wires are again concealed under the wire guide.

A thermistor in the printhead prevents burning caused by overheating of the coil during extended continuous bi-directional printing. When the temperature of the coil exceeds a predetermined limit (about 119°C) the control circuit detects a thermistor signal. Printing will then be intermittent or stop completely until the coil temperature falls below the limit value.

Figure 2-3

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Okidata ML321 Turbo, ML320 Turbo Service Manual

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