OKIDATA ML320 Turbo User manual

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Service Guide ML320/321Turbo
Chapter 0 About This Manual
ML320 Turbo // ML321 Turbo
Dot Matrix Printers
Adobe Acrobat printable reference
copy of the OKIDATA Service Training Manual.
09/17/97
Note: This Adobe Acrobat version of the Okidata Service Training Manual was built with the
pictures rendered at 300 dpi, which is ideal for printing, but does not view on most
displays well.
Okidata is a registered trademark, and OkiPage is a trademark of Oki Electric Industry Co., Ltd. HP,
LaserJet and PCL5e are trademarks of Hewlett-Packard Co. Adobe and Acrobat are trademarks of Adobe
Systems Incorporated.
Copyright 1997, Okidata, Division of OKI America, Inc. All rights reserved. See the OKIDATA Business
Partner Exchange (BPX) for any updates to this material. (http://bpx.okidata.com)

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

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Service Guide ML320/321Turbo
Chapter 1 Configuration
1.1. Standard Printer Configuration
This printer consists of the following assemblies:

Copyright 1997, Okidata, Division of OKI America, Inc. All rights reserved. See the OKIDATA Business
Partner Exchange (BPX) for any updates to this material. (http://bpx.okidata.com)

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Service Guide ML320/321Turbo
Chapter 1 Configuration
1.2 Options
(1) Cut sheet feeder unit (CSF)
Single-bin CSF
(2) Pull-tractor assy

(3) Bottom push tractor unit
(4) Roll paper stand (Narrow only)
(5) Serial I/F
- RS-232C

Copyright 1997, Okidata, Division of OKI America, Inc. All rights reserved. See the OKIDATA Business
Partner Exchange (BPX) for any updates to this material. (http://bpx.okidata.com)

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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.

Copyright 1997, Okidata, Division of OKI America, Inc. All rights reserved. See the OKIDATA Business
Partner Exchange (BPX) for any updates to this material. (http://bpx.okidata.com)

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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.

Copyright 1997, Okidata, Division of OKI America, Inc. All rights reserved. See the OKIDATA Business
Partner Exchange (BPX) for any updates to this material. (http://bpx.okidata.com)

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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.

Copyright 1997, Okidata, Division of OKI America, Inc. All rights reserved. See the OKIDATA Business
Partner Exchange (BPX) for any updates to this material. (http://bpx.okidata.com)

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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.
Copyright 1997, Okidata, Division of OKI America, Inc. All rights reserved. See the OKIDATA Business
Partner Exchange (BPX) for any updates to this material. (http://bpx.okidata.com)

Page: 8
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.
Print Compensation Control
The print compensation methods are shown below:
(a) Voltage compensation (See 2.1.8 "Alarm Circuit." )
(b) Temperature compensation (See 2.1.8 "Alarm Circuit." )
(c) Pin stroke compensation