OHAUS MB25 User manual

SERVICE MANUAL
Ohaus Corporation 7 Campus Drive, Suite 310, Parsippany, NJ 07054 USA [phone]

SERVICE MANUAL
The information contained in this manual is believed to be accurate at the time of publication, but Ohaus
Corporation assumes no liability arising from the use or misuse of this material. Reproduction of this
material is strictly prohibited.
Material in this manual is subject to change.
80252469D © Copyright 2013 Ohaus Corporation, all rights reserved.
TM Registered trademark of Ohaus Corporation.

TABLE OF CONTENTS
Ohaus Corporation www.ohaus.com i MB23 and MB25 Service Manual
CHAPTER 1 GETTING STARTED Page No.
1.1 Introduction..............................................................................................................1-1
1.2 Service Facilities......................................................................................................1-1
1.3 Tools and Test Equipment Required........................................................................1-2
1.4 Specifications...........................................................................................................1-3
1.5 Analyzer Operation ..................................................................................................1-4
1.5.1 Overview of the Controls...................................................................................1-4
1.5.2 Overview of the Display Indicators....................................................................1-4
1.5.3 Operating Modes ..............................................................................................1-5
1.5.4 Power ...............................................................................................................1-7
1.5.5 Power On & Off.................................................................................................1-7
1.6 Communications Interface........................................................................................1-8
CHAPTER 2 TROUBLESHOOTING
2.1 Troubleshooting.......................................................................................................2-1
2.1.1 General Procedures for Troubleshooting ..........................................................2-1
2.2 Error Codes..............................................................................................................2-2
2.3 Problem Solver ........................................................................................................2-4
CHAPTER 3 MAINTENANCE PROCEDURES
3.1 Preventive Maintenance...........................................................................................3-1
3.1.1 Preventive Maintenance Checklist....................................................................3-1
3.2 Opening the MB23 and MB25..................................................................................3-1
3.3 Preliminary Checks of the Top Housing Components ..............................................3-4
3.3.1 Test the Heater Circuit......................................................................................3-4
3.3.2 Test the Temperature Sensor and Cable..........................................................3-4
3.3.3 Test the Fan......................................................................................................3-4
3.3.4 Test the Ground Circuit on the MB23................................................................3-4
3.4 Testing the Power PCB............................................................................................3-5
3.5 Replacing the Power PCB........................................................................................3-5
3.6 Replacing the Main PC Board..................................................................................3-6
3.6.1 Replacing the Display LCD...............................................................................3-6
3.7 Replacing the Load Cell...........................................................................................3-7
3.8 Repairing and/or Replacing the Heating Unit Parts ..................................................3-8
3.8.1 Testing the Heater Circuit .................................................................................3-8
3.8.2 Removing the Heater on the MB23...................................................................3-9
3.8.3 Removing the Heater on the MB25.................................................................3-10
3.8.4 Replacing the Heater on the MB25 .................................................................3-10
3.8.5 Replacing the Heater on the MB23 .................................................................3-11
3.8.6 Testing the Thermal Overload Device.............................................................3-11
3.8.7 Replacing the Thermal Overload Device.........................................................3-12
3.8.8 Replacing the Fan...........................................................................................3-13
3.8.9 Replacing the Temperature Sensor.................................................................3-14
3.9 Installing the Top Housing......................................................................................3-15
CHAPTER 4 FINAL TESTING Page No.
4.1. Final Testing ............................................................................................................4-1
4.2 Operational Test ......................................................................................................4-1
4.3 Segment Display Test..............................................................................................4-1
4.4 Performance Tests...................................................................................................4-1

TABLE OF CONTENTS
MB23 and MB25 Service Manual ii Ohaus Corporation www.ohaus.com
CHAPTER 4 FINAL TESTING continued Page No.
4.4.1 Precision Test...................................................................................................4-2
4.4.2 Repeatability Test.............................................................................................4-3
4.4.3 Linearity Test....................................................................................................4-4
CHAPTER 5 DRAWINGS AND PARTS LISTS
5-1 MB23 and MB25: Housing & Internal Parts..............................................................5-2
Appendix A STANDARD CALIBRATION
A.1 Weight Calibration...................................................................................................A-1
A.2 Temperature Calibration..........................................................................................A-2
A.3 Service Calibration..................................................................................................A-3
Appendix B SOFTWARE SERVICE TOOL
B.1 Software service tool location..................................................................................B-1
LIST OF TABLES
TABLE NO. TITLE Page No.
1-1 Specifications ......................................................................................................1-3
1-2 Functions of Display Controls ..............................................................................1-4
2-1 Error Codes.........................................................................................................2-2
2-2 Problem Solver....................................................................................................2-3
4-1 Types of Performance Tests & Tolerances....................................................4-1
5-1 MB23 & MB25: Housing & Internal Parts.............................................................5-3
LIST OF ILLUSTRATIONS
FIGURE NO. TITLE
1-1 MB23 and MB25 Function Labels........................................................................1-4
1-2 MB23 & MB25 Display Indicators.........................................................................1-4
1-3 AC Power ............................................................................................................1-7
1-4 RS232 DB9-pin setup..........................................................................................1-8
1-5 Solder Points on PCB..........................................................................................1-8
3-1 MB25 with Top Open...........................................................................................3-2
3-2 Housing Chamber................................................................................................3-2
3-3 Lifting Out Plug in Housing ..................................................................................3-2
3-4 Clear Plastic In-use Cover...................................................................................3-2
3-5 Three screws in Top Housing ..............................................................................3-2
3-6 Lifting the Housing...............................................................................................3-3
3-7 Fan, Temperature Sensor, Heater cable connectors on Power PCB ...................3-3
3-8 Cables for Temperature Sensor, Fan, Ground and Heater disconnected.............3-4
3-9 Power PCB Connectors.......................................................................................3-5
3-10 Power PCB..........................................................................................................3-5
3-11 Load Cell Cover...................................................................................................3-6
3-12 Main Printed Circuit Board...................................................................................3-6
3-13 Display LCD on Main PCB...................................................................................3-6
3-14 Load Cell.............................................................................................................3-7
3-15 Load Cell with Ribbon Cable Attached at Bottom.................................................3-7
3-16 Screws Holding Chamber Top to the Heater Frame Housing...............................3-8
FIGURE TITLE Page No.
3-17 Separating the Chamber Top from the Heater Frame Housing............................3-8
3-18 Testing Heater Leads’ Resistance.......................................................................3-8

TABLE OF CONTENTS
Ohaus Corporation www.ohaus.com iii MB23 and MB25 Service Manual
3-19 Screws and Washers that Secure the Reflector...................................................3-9
3-20 MB23: Screws and washers anchoring cables on each side of Heater ................3-9
3-21 Spring Tab on Connector.....................................................................................3-9
3-22 Lifting Out the Heater (MB23)..............................................................................3-9
3-23 Screw and washer anchoring Heater Cables.....................................................3-10
3-24 Lifting Out the Heater (MB25)............................................................................3-10
3-25 MB23: Installing the Heater................................................................................3-11
3-26 Reset Button on the Thermal Overload Device..................................................3-11
3-27 MB25 Thermal Overload Device........................................................................3-12
3-28 MB23 Thermal Overload Device........................................................................3-12
3-29 MB 25 Thermal Overload Device Installed.........................................................3-12
3-30 Screws in Fan Plate...........................................................................................3-13
3-31 Grommets Slide Out from the Bottom Plate.......................................................3-13
3-32 Lid Position Rod and Spring under the Fan Plate ..............................................3-13
3-33 Removing the Fan .............................................................................................3-12
3-34 Removing Screw to Access Temperature Sensor Cable....................................3-14
3-35 Removing Clip that Secures Heater, with Needle Nose Pliers ...........................3-14
3-36 Removing Screws and Washers Securing Temperature Sensor........................3-14
3-37 Connecting Cables to the Power PCB ...............................................................3-15
3-38 Placing Plug on Top Housing.............................................................................3-15
3-39 Installing Protective Glass..................................................................................3-15
3-40 Clear plastic In-use Cover..................................................................................3-16
3-41 Housing Chamber..............................................................................................3-16
3-42 MB25 with top open...........................................................................................3-16
4-1 Segment Display .................................................................................................4-1
5-1 MB23 & MB25: Housing & Internal Parts.............................................................5-2
A-1 Temperature Calibration Kit installed..................................................................A-1

TABLE OF CONTENTS
MB23 and MB25 Service Manual iv Ohaus Corporation www.ohaus.com

CHAPTER 1 GETTING STARTED
MB23 and MB25 Service Manual 1-1 Ohaus Corporation www.ohaus.com
1.1 INTRODUCTION
This service manual contains the information needed to perform routine maintenance and
service on the MB23 and MB25 Moisture Analyzers. Familiarity with the Instruction Manual is
assumed. The contents of this manual are contained in five chapters:
Chapter 1 Getting Started –Contains information on service facilities, tools, specifications,
and the mechanical and electronic functions of the product.
Chapter 2 Troubleshooting –Contains a diagnostic guide and error code table.
Chapter 3 Maintenance Procedures –Contains preventive maintenance procedures and
disassembly, repair and replacement procedures.
Chapter 4 Testing –Contains a list of required test masses, an operational test, segment
display test, performance tests and adjustments.
Chapter 5 Drawings and Parts Lists –Contains exploded views of MB23 and MB25 Moisture
Analyzers identifying all serviceable components.
Appendix A Standard Calibration –Explains procedures for Standard Calibration, performed
prior to use and after service.
1.2 SERVICE FACILITIES
The service area should meet the following requirements:
Should be temperature controlled and meet specifications for temperature environmental
requirements.
Must be free of vibrations such as fork lift trucks close by, large motors, air currents or
drafts from air conditioning/heating ducts, open windows, people walking by, fans, etc.
Area must be clean and free of excessive dust.
Work surface must be stable and level.
Moisture Analyzers must not be exposed to direct sunlight or radiating heat sources.
Use an approved Electro-Static Device.

CHAPTER 1 GETTING STARTED
Ohaus Corporation www.ohaus.com 1-2 MB23 and MB25 Service Manual
1.3 TOOLS AND TEST EQUIPMENT REQUIRED
1. Digital Voltmeter (DVM) - Input impedance of at least 10 megohms in 1 Volt dc position.
2. Standard electronics tool kit
3. Soldering iron (50 watt) and solder (rosin core solder, not acid core).
4. Solder remover
5. Ohaus Temperature Calibration Kit P/N 11113857
6. 50g calibration weight
7. Strain Gage Simulator (optional)
8. Soft, lint-free cleaning cloth
9. Anti-static bags for PCBs
10. Anti-static wrist strap and mat
11. RS232 Cable, P/N 80500525