OHAUS EB SERIES, Service Manual

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CHAPTER 2 DIAGNOSIS
EB Series Scales Series Service Manual 2-9 Ohaus Corporation www.ohaus.com
2.8 TESTING THE MAIN PC BOARD
The Main PC Board can be tested by measuring voltages and by using a simulator. The
simulator replaces the Load Cell during testing and is a useful tool for diagnosing problems.
2.8.1 Main PC Board Voltage Measurements
Prior to making the voltage measurements, the battery should have been fully charged and
tested.
1. Disconnect power from the scale.
2. Remove the Top housing, refer to Section 3.1 and leave the Membrane Switch
connected to the scale.
3. Disconnect the battery from the Main PC Board.
4. Remove screws and washers holding the Main PC Board and lift out the board and
lay it flat.
5. Connect the AC Adapter to the scale.
6. Refer to Figure 2-2, Interconnection Diagram which illustrates the interconnections to
the Main PC Board and is shown as a top view.
7. Turn the scale on.
8. Using a DVM, measure the excitation voltage EXE and -EXE leads it should
be 5 volts dc. This is the excitation voltage for the Load Cell and is regulated. If the
voltage is lower, replace the Main PC Board, refer to Section 4.3 and then proceed
with Performance Tests in accordance with Chapter 4.
9. Measure incoming power from the AC Adapter connector shown in Figure 2-2. The
voltage should read above 6 Volts dc with power on.
10. Connect the battery to the Main PC Board and measure the voltage across Black
and Red leads on the battery connector. The full battery voltage should read a
minimum of 6.0 Volts dc. If the voltage is lower, the battery may require charging or it
may be defective. Refer to Section 2.7 and test the battery.
11. Perform simulator testing.
2.8.2 Simulator Testing
To perform these tests, the use of a Simulator is required. The basic function of a Simulator is to
simulate the output of a full bridge Load Cell allowing the scale to be separated from the Load
Cell for the purposes of troubleshooting and calibration. The Load Cell used in the scale is rated
at 2mV/V output with a 5 Volt excitation voltage applied.