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Field Service Procedure – Replacement PCU Kit, ST88, ST94 & ST144
Page 4 of 22
Document No
137738 Rev A
Copyright © Sea Tel, Inc 2012 - The information contained in this document is proprietary to Sea
Tel, Inc. This document may not be reproduced or distributed in any form without prior written
consent of Sea Tel, Inc.
7.2. Error Types.
The 3 types of pedestal error are.....
1. Servo Limit (CL, LV and AZ ) – A servo limit error means the PCU motherboard is issuing the command to the
motor driver enclosure to drive the relevant axis harder than it should under normal operation (the servo limit has
been reached). This could be whilst the antenna is trying to maintain its pointing angle, or whilst the antenna is
driving the axis to a target position.
2. Stability Limit – A stability limit error means the antenna has mispointed from its desired target position by more
than half a degree. When a stability limit error is flagged on a VSAT antenna the DAC will send the TX Mute
command to inhibit the transmit function of the satellite modem (It’s common to see the servo limit and stability
limit errors together).
3. AZ Reference Error – An azimuth reference error means there is a corrupt reading in the antennas relative scale.
This could be caused by the system completing a 360 degree rotation without the sensor coming into contact with
the home flag, the sensor coming into contact with the home flag too early, or a physical problem such as the chain
or belt slipping on the motor pulley or the pulley slipping on the motor shaft.
7.3. Troubleshooting Pedestal Errors – Servo Limit and Stability Limit.
1. Reinitialize the pedestal. Does it drive correctly or not at all? ‐ If none of the axis drive verify the N0 and motor gain
parameters (N1 = CL, N2 = EL and N3 = AZ) are correctly configured in the PCU through the Remote Command
window of the DAC.
2. Verify the balance of the antenna and check for physical restrictions on the pedestal. If the axis isn’t correctly
balanced the PCU will be outputting additional drive commands to maintain the antennas level position.
3. If the motor isn’t driving correctly or no motor drive is present, test the motor for faults using the procedure in
section 8 of this document. If you find the motor is defective replace it and then test the function of the motor
driver. If the axis still fails to drive correctly the motor may have damaged it. Replace the motor driver.
4. Verify if the brakes have released properly. If the movement of the axis is restricted measure the output to the
motor to verify if the 12VDC is present. If so the brake hasn’t released the motor is defective. If the 12VDC isn’t
present trouble shoot the harness / motor driver enclosure.
5. Another potential problem could be a damaged or intermittent harness connection. Remove the harness back
shells and verify all the pins are seated correctly, check continuity from pin to pin and also across the pins to verify
there is no short in the connections.
7.4. Troubleshooting Pedestal Errors – Azimuth Reference Error.
1. Reinitialize the system and verify the sensor comes into contact with the home flag as the system drives clockwise
in azimuth (the LED will illuminate). If not verify if the home flag/sensor is present, if correct then it’s a
sensor/feedback failure.
2. Drive the azimuth axis in 90 degree increments and verify that the antenna points correctly and that the DAC
displays the correct relative position. Also verify that there is no physical restriction on the azimuth axis such as the
chain or belt slipping on the motor pulley or the pulley slipping on the motor shaft.