4.28.3.1 Verify if the Bearing PWM Amplifier is Draining Energy
1. Remove the Service Side Cover. Refer to Section 4.1.3.1 Service Side Cover Removal and Installation on
2. Disable compressor operation while keeping the compressor energized.
3. Measure and record the voltage at the HV+, +17HV, and +5V test points on the Backplane.
4. Isolate compressor power.
5. Wait for the LEDs on the Backplane to turn off.
6. Disconnect the rear/axial bearing current output cable and the front bearing current output cable.
7. Apply power to the compressor.
8. Measure and record the voltage at the HV+, +17HV, and +5V test points.
9. Isolate compressor power.
10. Wait for the LEDs on the Backplane to turn off.
11. Remove the PWM from the Backplane. Refer to Section 4.28.4 PWM Removal and Installation on page
12. Apply power to the compressor.
13. Measure and record the voltage at the HV+, +17HV, and +5V test points.
14. If the voltages do not change, the PWM is not the source (or not the only source) of energy drain.
4.28.3.2 Verify Functionality of the Five Output Channels
1. Verify the bearing coil resistances are within specification. Refer to Section 4.29.3 Bearing Verification
2. Verify the bearing sensor resistances are within specification. Refer to Section 4.29.3 Bearing
3. Verify the voltages at the HV+, +17HV, and +5V Backplane test points are within the expected voltage
ranges shown in Table 4-42 Backplane Test Point Values on page 215.
4. Perform a bearing calibration using the SMT.
5. Watch the bearing forces while the compressor is going through its calibration steps. The software
should display both a positive and negative bearing amperage for each bearing position (Front Radial
X, Front Radial Y, etc.). If you do not see bearing amperage at all, or in only one direction (+/-), its
possible the PWM is faulty on that channel assuming the bearing coil verified in Step 1 was good.
NOTE
If one of the PWM output channels has failed, the corresponding bearing channel returns a gain of 0 when a bearing calibration is
performed.
6. If all bearing resistances are good and one or more of the gains is/are 0, but not all the gains are 0, the
PWM could be faulty.
4.28.3.3 Verify Functionality of the Five Diode Sets
To verify the diode sets within the PWM channels, complete the following steps:
1. Isolate compressor power as described in Section 1.8 Electrical Isolation on page 22.
2. Remove the Service Side Cover. Refer to Section 4.1.3.1 Service Side Cover Removal and Installation on
3. Verify the LEDs on the Backplane have turned off.
4. Unplug the 250VDC input (J4) from the Backplane. Refer to Figure 4-238 Backplane Connections on
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Summary of Contents for Turbocor TT Series
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