OHAUS EB SERIES, Service Manual

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CHAPTER 2 DIAGNOSIS
Ohaus Corporation www.ohaus.com 2-10 EB Series Scales Series Service Manual
2.8.2.1 General Load Test
This test checks the Main PC Board circuitry by simulating accurate load cell voltages at 0%,
50% and 100% load capacities.
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.
4. Unsolder the Load Cell cable from the Main PC Board. Refer to Figure 2-2 for
location.
5. With the Simulator set to zero, connect the Simulator test leads to the Main PCB by
soldering test leads in place of the load cell. Make sure connections are correct.
6. Connect a known good AC Adapter to the scale and connect to a power source.
7. Turn on the scale, an error may be displayed. This is normal.
8. Review Table 2-10 and adjust the Simulator to simulate 0% load, 50% load and
100% load for the rated capacity of the scale. If the resulting readings are unstable,
the Main PC Board is defective. Use the Simulator to calibrate the scale in the next
procedure to verify if the Main PC Board is good or bad.
2.8.2.2 Calibration Test
This test calibrates the scale using the simulator and can verify that the Main PC Board is
functioning properly or improperly.
1. With the scale on and the Membrane Switch connected, enter calibration mode by
pressing and holding the Zero switch until CAL is displayed and perform calibration.
2. Follow the scale prompts. When the scale indicates a given weight should be placed
on the scale, set the simulator to an equivalent value based on Table 2-10. For
example, when a span value of 3 kg for a 3 kg scale is shown, the simulator should
be set to output 9.1mV (2.7 + 6.4).
3. Upon completion of calibration, the Main PC Board can be further checked using the
Simulator to simulate various weight values. If simulator settings and weight reading
on the scale agree, the Main PC Board is functional. If the scale readings vary, or do
not agree with readings in Table 2-10, the Main PC Board is defective and should be
replaced.
4. Remove power from the scale and proceed with Section 3.3 and replace the Main
PC Board.
5. After Main PC Board replacement and assembly of the scale, proceed with
Performance Tests in Chapter 4.