OHAUS SD Series, Руководство по обслуживанию

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CHAPTER 2 TROUBLESHOOTING
2.4.3 Testing the Printed Circuit Board (PCB)
The PCB 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.
PCB Voltage Measurements
Note: Prior to the voltage measurements, test and install new batteries.
1. Disconnect the power and remove the Top Housing.
2. Connect the AC Adapter to the Indicator and turn it on.
3. Using a DVM, measure the excitation voltage (EXE+ and EXE– in Figure 2-1.)
The reading should be 3 volts dc. This is the excitation voltage for the Load Cell
and is regulated. If the voltage is lower, replace the PCB. (See Chapter 3.)
Then perform Operational Tests. (See Chapter 4.)
4. Measure incoming power from the AC Adapter Connector. (See Figure 2-1.) It should
read between 9 and 14 volts dc with power off and above 9 Volts dc with power on.
5. Perform simulator testing.
Simulator Testing
To perform these tests, the use of a Simulator is required. The 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.
General Load Test
This test checks the Main PC Board circuitry by simulating accurate Load Cell voltages at zero
load, 50% and 100% load capacities.
1. Disconnect power from the Indicator, and remove the Top housing.
Remove the batteries.
2. Disconnect the Load Cell cable from the PC Board.
3. With the Simulator set to zero, attach it to the PCB, using the Load Cell Cable solder
points on the PCB. (See Figure 2-1.).
4. Connect a known good AC Adapter to the Indicator and connect to a power source.
5. Turn on the Indicator. An under load error may appear. This is normal.
6. Set the Indicator to indicate weight in kilograms (kg) and set the calibration value to
maximum span value.
7.
Adjust the Simulator to simulate 0% load, 50% load and 100% load for the capacity
that the unit is rated for. (See Table 2.3 for values to use.) If the resulting readings
are unstable, the Main PC Board is defective.
8.
Use the Simulator to calibrate the scale in the next procedure.
Ohaus Corporation www.ohaus.com 2-6 SD Series Scales Service Manual