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4.29.3 PWM Verification
Several verification methods are available for the PWM:
• Verify if the PWM is draining energy.
• Verify functionality of the five output channels.
• Verify functionality of the five (5) diode sets.
4.29.3.1 Verify if the Bearing PWM Amplifier is Draining Energy
1. Remove the Service Side Cover. Refer to "4.2.3.1 Service Side Cover Removal and Installation"
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 as described in Section "1.8 Electrical Isolation" on page 19.
5. Wait for the LEDs on the Backplane to completely 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 as described in Section "1.8 Electrical Isolation" on page 19.
10. Wait for the LEDs on the Backplane to completely turn off.
11. Remove the PWM from the Backplane. Refer to "4.29.4 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.
4.29.3.2 Verify Functionality of the Five Output Channels
1. Verify the bearing coil resistances are within specification.
2. Verify the bearing sensor resistances are within specification.
3. Verify the voltages at the HV+, +17HV, and +5V Backplane test points are within the expected
voltage ranges shown in "Table 4-43 Backplane Test Point Values" on page 211.
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 is faulty.
NOTE
A faulty PWM Amplifier may be the result of a bearing failure and may cause a failure of the DC-DC resulting in a blown F1 fuse on
the Soft Start.
If a PWM Amplifier is found to be faulty, the bearing actuator coils, DC-DC and F1 Fuse must also be verified.
Summary of Contents for Turbocor TTS Series
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