About This Manual
ML520 // ML521 Dot Matrix Printers
 Service Guide ML520/521
 Maintenance & Disassembly
 Failure & Repair Analysis
 Illustrated Parts Listing
 Table of Contents
 Service Guide ML520/521
Page
 Product Specifications General Information
 Microline
Printer Weight Microline
 Power Requirements
Product Specifications
 Altitude
Ambient Temperature and Relative Humidity RH
 Product Specifications Agency Approvals 1.5.01 Listings
 Horiz. DPI Vert. DPI
CPI CPS
IPS
HSD
 UPC a UPC E EAN
 Graphics Resolution
Front Panel Switches
Emulations
Fonts Near Letter Quality
 Line Feed Increments Fixed
Menu Mode Switch Action
Selects Group Function
Form Feed / Load Selects Item
 Paper Out Detection
Paper Loading
Paper Tear Capabilities
Print Method Printhead Type General Information
 Gap Control
Printhead Gap Adjustment
Auto Gap
Semi Auto Gap
 80 12 cpi 320 12 cpi 427 12 cpi
Print Modes
 Types Card Stock
Paper Specifications
Continuous Form
Cut Sheet
 Labels
Envelopes
Transparency
 Length
Weight
Number of Copies
Thickness
 Paper
Width
Printing Area
 Eeprom
Memory Specifications
Eprom
03 RAM
 Product Specifications Consumables 1.9.01 Ribbon
 Dual Bin
Page
 Product Specifications Pull Tractor Kit
 Product Specifications Bottom Push Tractor Kit
 Product Specifications Serial Interface
 Product Specifications Roll Paper Stand
 OKISmart Panel Utility
Product Specifications OKISmart Typer Utility
 Reliability
 Electrical Operation
Principles of Operation
 Principles of Operation Main Control Board
 Principles of Operation Block Diagram
 Principles of Operation Program ROM
 RAM
 LSI
 Service Guide ML520/521
 Principles of Operation Initialization
Reset operation initiated by I-PRIME does not reset the MPU
 Principles of Operation Parallel Interface Control
 Principles of Operation Print Control
 Principles of Operation LSI/Printhead Interface
 Principles of Operation Gap Adjust Control
 Also refer to .1.07 Head Drive Time
Principles of Operation Print Compensation Control
 Service Guide ML520/521
 Principles of Operation Line Feed Motor Control
 Principles of Operation Space Motor Control
 Principles of Operation Encoder Disk
 Principles of Operation Operation Panel
Page
 Service Guide ML520/521
 Principles of Operation Low Motor Drive Voltage Alarm
 Principles of Operation Head Drive Time
 +34 vdc or greater
Less than 50%
 Principles of Operation Head Overheat Alarm Processing
 Voltage/Signal Purpose
Principles of Operation Power Supply Circuit
 Service Guide ML520/521
 Principles of Operation Printhead Gap Information
Page
 Service Guide ML520/521
 Principles of Operation Line Feed Motor Resistance
 Principles of Operation Space Motor Resistance
 Principles of Operation Printhead Operation
Page
 Principles of Operation Printhead Temperature
 Principles of Operation Spacing Mechanism
 Principles of Operation Spacing Operation
 Principles of Operation Head Gap Mechanism
Head Gap Setting Operation
Page
 Principles of Operation Ribbon Drive Operation
Page
 Change Lever Paper Path Selection Lever
Principles of Operation Line Feed Mechanism
Paper Clamp Mechanism
Page
 Rear/Bottom Feed for continuous feed paper
Page
 Principles of Operation Cut Sheet Paper Feed Operation
 Service Guide ML520/521
 Service Guide ML520/521
 Service Guide ML520/521
 Service Guide ML520/521
 Bottom Feed Detection
Rear Feed Detection
Page
 Principles of Operation Support Protector Mechanism
 Cut Sheet Paper
Principles of Operation Automatic Paper Load
 Principles of Operation Continuous Feed Paper
 Paper Park Operation
Principles of Operation Paper Park
 Maintenance & Disassembly General Information
 Maintenance & Disassembly Maintenance Tools
 Handbook when the any of the following occur
Maintenance & Disassembly Maintenance Precautions
 Service Guide ML520/521
 Maintenance & Disassembly Preliminary Items
Page
 Perform this procedure
Maintenance & Disassembly Printhead Assembly
Page
 Perform these procedures 3.2.01 ,
Maintenance & Disassembly Ribbon Protector
53562801 Protector Ribbon Rspl Both B.2.07
 Maintenance & Disassembly Gear Case Assembly
 Maintenance & Disassembly Pull-up Roller Assembly
 When cleaning, refer to .4 of this Service Handbook
Page
 Installation
Maintenance & Disassembly Control Board Fjim
Page
 Maintenance & Disassembly Power Supply Assembly
Page
 Perform these procedures 3.2.01 , 3.2.06 ,
Maintenance & Disassembly Operator Panel PCB Leop
 Perform these procedures 3.2.01 , 3.2.02 ,
Maintenance & Disassembly PC Connector
 56729601 Connector PC HD40 Rspl Both B.2.07
 Perform these procedures 3.2.01 , 3.2.02 , 3.2.04 ,
Page
 Perform these procedures 3.2.01 , 3.2.06 , 3.2.07 ,
Maintenance & Disassembly Carriage Cable
 When cleaning, refer to .4 of this Service Handbook
Maintenance & Disassembly Space Rack
Page
 Maintenance & Disassembly Roller/Holder Backup Assembly
 Maintenance & Disassembly Guide Rail and Adjust Cam
Page
 51010301 Plate Left Ground Rspl Both B.2.04
Maintenance & Disassembly Left Ground Plate
 51010201 Plate Right Ground Rspl Both B.2.05
Maintenance & Disassembly Right Ground Plate
 Perform these procedures 3.2.01 , 3.2.06 , 3.2.07 , 3.2.16 ,
 When lubricating, refer to .5 of this Service Handbook
Maintenance & Disassembly Platen Assembly
Page
 Maintenance & Disassembly Paper Chute Assembly
Page
 Maintenance & Disassembly Line Feed Motor Assembly
 56627201 Cord Connection Line Feed Rspl Both B.2.04
 50923201 Spring Reset Rspl Both B.2.05
Maintenance & Disassembly Reset Spring
 Maintenance & Disassembly Idle Gear and Change Lever
Page
 Maintenance & Disassembly Pressure Spring
Page
 Maintenance & Disassembly Carriage Shaft
Page
 Maintenance & Disassembly Leaf Spring
Page
 Maintenance & Disassembly Bottom Paper Sensor Levers
Page
 Maintenance & Disassembly Front Pressure Roller Assembly
Page
 Maintenance & Disassembly Tractor Assembly
Page
Page
 Maintenance & Disassembly Main Frame
 Service Guide ML520/521
 Procedure Setup Phase
 Parallel Adjustment Phase
Printhead Gap Modification Phase
Verification Phase
Page
 SEL + FF/LOAD
Maintenance & Disassembly Key Combinations Description
 Printing the Menu
Menu Mode
 Procedure
Reset Menu to Factory Defaults
Limited Operation General Information
Page
 Group Setting
Maintenance & Disassembly Menu Settings
 Valid
 Yes No
Page
 Setting Top of Form
Maintenance & Disassembly Top of Form General Information
Reset the Top of Form to Factory Default
 Procedure Continuous Feed to Single Sheet
Maintenance & Disassembly Paper Park General Information
Procedure Single Sheet to Continuous Feed
 Maintenance & Disassembly Tear Feature
 Vertical Line Spacing Problems
Maintenance & Disassembly Forms Tear Off
 Checking Top of Form with Form Tear Off Activated
Using
 Factory default Top of Form Setting is 1 inch
 Cleaning
Maintenance & Disassembly
Cleaning Schedule
Cleaning Tools
 Lubrication Schedule
Lubrication
Lubrication Types
Lubrication Amounts
 Areas Not Lubricated
 Shipping Instructions
Return for Service
All Other Returns
 Failure & Repair Analysis Introduction
 Service Guide ML520/521
 Header
Failure & Repair Analysis Firmware Revision Identification
 Service Guide ML520/521
 Failure & Repair Analysis Problem Lists
 Course Critique
Failure & Repair Analysis Reporting Methods Okilink
Fax Number
Mailing Address
 Okilink
Technical Service Bulletins
Faxable Facts
 Service Guide ML520/521
 Alarm Lamp Blinks Fatal Errors
Failure & Repair Analysis Problem Categories
Operational Errors
Alarm Lamp Lights Paper End/Jam Conditions
 Start
Failure & Repair Analysis Start Here Flowchart
 This Service Handbook
Failure & Repair Analysis Tips for Preventing Image Problems
 Failure & Repair Analysis Common Problems
 Always power OFF the printer before you turn the platen knob
Page
 Uneven Print Density
 Inconsistent Line Feed
Smeared Print
 Drifting Margin
 Failure & Repair Analysis Left Margin Drifting Problem
 Failure & Repair Analysis
Fault Alarms
 Alar Utility PRO NLQ HSD Menu
 Blinkin Kin
 Refer to RAP
Page
 Service Guide ML520/521
 Failure & Repair Analysis RAP Index RAP Number Description
 Start
Page
 Failure & Repair Analysis RAP 02 No Spacing Operation
Page
 Failure & Repair Analysis RAP 03 Printhead Homing Error
Page
 Service Guide ML520/521
 Failure & Repair Analysis RAP 05 Printhead Pins Not Firing
 Failure & Repair Analysis RAP 06 Poor Print Quality
 Failure & Repair Analysis RAP 07 Ribbon Feed Problem
 Failure & Repair Analysis RAP 08 Line Feed Problem
Page
 Failure & Repair Analysis RAP 09 Operation Panel Malfunction
 Failure & Repair Analysis RAP 10 Parallel Interface Problem
Page
 Failure & Repair Analysis RAP 11 Serial Interface Problem
 Handbook
 Printer Tests
 Procedure
Page
 Failure & Repair Analysis Font Test General Information
Page
 Failure & Repair Analysis Serial Interface Loopback Test
Loopback Connector Configuration
Page
 Failure & Repair Analysis Serial Cable Information
 Service Guide ML520/521
 Service Guide ML520/521
 Hex Data Dump
Example
 Service Guide ML520/521
 Layout Diagram
 Service Guide ML520/521
 Failure & Repair Analysis Line Feed Motor Resistance
 Failure & Repair Analysis Space Motor Resistance
 Service Guide ML520/521
 Description Board Designation Section Main Controller Board
Chapter a Reference Charts
Operator Panel Board
 Chapter a Reference Charts Board Layout
 Firmware
Switches
Fuses
Jumpers
Page
 Shift
Page
 Chapter a Reference Charts Power Supply Assembly Function
Page
 Chapter a Reference Charts Space Motor Board Function
Page
 Masked to the MPU Socket is empty
Page
 Service Guide ML520/521
 Chapter B Illustrated Parts Listing Format
 Remember
Chapter B Illustrated Parts Listing Current Part Numbers
 Rspl
 521
520
Both
 Placing a Parts Order
 Charts
 Chapter B Illustrated Parts Listing Overview
 Refer to
Comments
 Comments Refer to
 53067201 2PA4094-7382G1 Cover Access Wide Rspl
 ROM
 PCB Leop
 Service Guide ML520/521
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 Service Guide ML520/521
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 Service Guide ML520/521
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Page
 Service Guide ML520/521
 N/A
 Service Guide ML520/521
 PCB Lxhi
 Service Guide ML520/521
 PCB Ncsf
 52107001 N/A Ribbon Black Consumable Both
Chapter B Illustrated Parts Listing Consumables
 To B.1.02
Comments Refer
 Service Guide ML520/521
Page
 Okidata P/N Oki-J Description
 Comments Refer
 Comments Refer