Oki ML421 Series User manual
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Oki Data CONFIDENTIAL
ML420/421 PRINTER
Maintenance Manual
ODA
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PREFACE
This maintenance manual describes how to maintain the ML420/421 printer in the field.
This manual is for customer engineers.
For further information, refer to the Users Manual for handling or operating the equipment.
The relation between the destination point and the model name of this printer is as follows.
For ODA ML420* ML421
* ML420 has a standard color and a Dell color (black).
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Contents
1. CONFIGURATION ...............................................................................................6
1.1 Standard Printer Configuration ............................................................................................ 6
1.2 Options................................................................................................................................. 7
2. THEORY OF OPERATION ..................................................................................9
2.1 Electrical Operation.............................................................................................................. 9
2.1.1 Summary................................................................................................................. 9
2.1.2 Microprocessor and the Peripheral Circuit.............................................................. 9
2.1.3 Initialization ........................................................................................................... 16
2.1.4 Interface Control ................................................................................................... 17
2.1.5 Print Control .......................................................................................................... 20
2.1.6 SP/LF Motor Control ............................................................................................. 22
2.1.7 Operation Panel .................................................................................................... 25
2.1.8 Alarm Circuit ......................................................................................................... 27
2.1.9 Power Supply Circuit............................................................................................. 30
2.2 Mechanical Operation ........................................................................................................ 31
2.2.1 Printhead Mechanism and Operation ................................................................... 31
2.2.2 Spacing Operation ................................................................................................ 34
2.2.3 Head Gap Adjusting.............................................................................................. 35
2.2.4 Ribbon Drive ......................................................................................................... 37
2.2.5 Paper Feed Operation .......................................................................................... 38
2.2.6 Paper Detection Mechanism................................................................................. 48
2.2.7 Automatic Sheet Feed .......................................................................................... 50
2.2.8 Paper Park Function ............................................................................................. 52
3. ASSEMBLY/DISASSEMBLY..............................................................................53
3.1 Precaution for Parts Replacement ..................................................................................... 53
3.2 Service Tools ..................................................................................................................... 54
3.3 Disassembly/Reassembly Procedure ................................................................................ 55
3.3.1 Printhead............................................................................................................... 57
3.3.2 Ribbon Protector ................................................................................................... 58
3.3.3 Pull-up Roller Assy................................................................................................ 59
3.3.4 Upper Cover Assy, Access Cover Assy and Sheet Guide Assy ........................... 60
3.3.5 Gear Case Assy.................................................................................................... 61
3.3.6 PC Connector ....................................................................................................... 62
3.3.7 Space Motor, Guide Roller Assy........................................................................... 63
3.3.8 Space Rack........................................................................................................... 64
3.3.9 Carriage Cable...................................................................................................... 65
3.3.10 Backup Roller Holder Assy ................................................................................... 66
3.3.11 Platen Assy ........................................................................................................... 67
3.3.12 Control Board (NNS)............................................................................................. 68
3.3.13 LF Motor................................................................................................................ 69
3.3.14 Operation Panel Board (LEOP) ............................................................................ 70
3.3.15 Power Supply Board (TPW).................................................................................. 71
3.3.16 Transformer Assy.................................................................................................. 72
3.3.17 Change Lever and Gears...................................................................................... 73
3.3.18 Carriage Shaft....................................................................................................... 74
3.3.19 Paper Pan ............................................................................................................. 75
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3.3.20 Rear Tractor Assy ................................................................................................. 76
3.3.21 Rear Pressure Assy .............................................................................................. 77
3.3.22 Switch Lever ......................................................................................................... 78
4. ADJUSTMENT ...................................................................................................79
5. CLEANING AND LUBRICATION .......................................................................87
5.1 Cleaning............................................................................................................................. 87
5.2 Lubrication ......................................................................................................................... 88
6. TROUBLESHOOTING AND REPAIR ................................................................95
6.1 Items to Check Before Repair............................................................................................ 95
6.2 Troubleshooting Table ....................................................................................................... 95
6.3 Lamp Display ..................................................................................................................... 96
6.4 Connection Circuit Check for Printhead and SP/LF Motor............................................... 100
6.5 Troubleshooting flow chart............................................................................................... 102
APPENDIX A PCB LAYOUT...............................................................................114
APPENDIX B SPARE PARTS LIST....................................................................115
APPENDIX C RS-232C SERIAL INTERFACE BOARD (OPTION)....................126
1. GENERAL............................................................................................................................ 126
2. OPERATION DESCRIPTION .............................................................................................. 126
2.1 Element Description .................................................................................................. 126
2.2 Circuit Description ..................................................................................................... 127
2.2.1 Operation at power on.................................................................................... 127
2.2.2. RS-232C interface.......................................................................................... 127
2.3 Communication Procedure Flowchart ....................................................................... 128
2.3.1 Mode a .......................................................................................................... 128
2.3.2 Mode b .......................................................................................................... 129
3. TROUBLESHOOTING FLOWCHART ................................................................................. 130
3.1 Before Repairing a Fault............................................................................................ 130
3.2 Troubleshooting ......................................................................................................... 130
3.3 Local Test .................................................................................................................. 133
3.3.1 Circuit test mode ............................................................................................ 133
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1. CONFIGURATION
1.1 Standard Printer Configuration
This printer consists of the following assemblies:
Figure 1-1 Configuration
Upper cover
Access cover assy
Platen knob
Sheet guide assy
Control board
Power supply board
Transformer assy Pull-up roller assy
Main chassis assy
Operation panel assy
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1.2 Options
(1) Cut sheet feeder unit (CSF)
(Narrow and wide versions available)
Dual-bin CSF Single-bin CSF
(2) Pull-tractor assy
Attachment assy Attachment assy
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(3) Bottom push tractor unit
(4) Roll paper stand (Narrow only)
(5) RS232C Serial interface board
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2. THEORY OF OPERATION
2.1 Electrical Operation
The electrical operation of the printer circuit is described in this section.
2.1.1 Summary
Figure 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.
2.1.2 Microprocessor and the Peripheral Circuit
(1) Microprocessor
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 ×1
• 16-bit automatic reload timer ×2
• 8-bit serial port ×2
• 8-bit parallel port ×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.
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Figure 2-1
HTEMP
14.456
MHz
4
POWLEV
HTEMP
HEADGAP
SPTEMP
A/D
PE-SENSOR
OPERATION
PANEL Serial
Alarm
-circuit HD alarm
Over-V alarm
Over-V alarm
FAN alarm
Power-off
Transformer Rectifier
circuit
50 volt
12 volt
5 volt 42V
-8V
3.3V
5VS
Reset
circuit
I/F-IPT
Print-IPT
EEPROM
1Kbits
Microproce-
ssor
ADDRESS
Serial
Serial
ROM
4Mbit
AD-BUS
DRAM
4Mbit
LSI
RESET
5VD
POWLEV
Fuse
42 V
SP/LF
driver
HD alarm
SPTEMP
Head
driver
Photo sensor
HEAD
M
M
SP
Thermister
LF
FAN
HTEMP
(opt.)
Serial-
I/F
(opt.)
Roll paper
stand
(opt.)
CSF
AC-input
SW
AC Fuse
Divider
Converter
Release-SW
Bottom-SW
HEADGAP-SWHEADGAP
Para-
I/F
USB
I/F
M
USB
Controller
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