Oki ML420 Maintenance Manual

42113901TH01 Rev.3 4 /
Oki Data CONFIDENTIAL
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

Oki ML420 Specifications

General

Brand	Oki
Model	ML420
Category	Printer
Language	English