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Field Service Procedure – Replacement PCU Kit, ST88, ST94 & ST144
1.
Brief Summary:
Troubleshooting document for diagnosing a fault with and replacing the PCU assembly on the ST88, ST94 and ST144
antennas.
2.
Checklist:
Verify Initialization
Measure the Power Supply Input / Output Voltages
PCU Status
Pedestal Error
Verify Stabilization
Verify Targeting
Test for Azimuth Drift
Verify the Communications Path
Test Pol Drive
3.
Theory of Operation:
The MK2 PCU assembly contains the 24VDC pedestal power supply (kit: 135341), PCU motherboard PCB (kit: 135338),
motion platform PCB (kit: 135342) and above decks 400MHz modem PCB (kit: 135349).
The PCU motherboard calculates the amount of movement from the vessel based on the feedback from the sensors on
the motion platform PCB and directional changes from the vessels gyro compass which are fed into the control loop. It
then sends the command to the MDE enclosure to drive the relevant axis by an equal and opposite amount of movement
to maintain stabilization and control the antennas dishscan pattern. The PCU software configures the function of the
pedestal and is calibrated by the N0 parameter which sets the motor gains for the size of the antenna as well as
configuring the dishscan pattern. The MK2 XX09 PCU Motherboard PCB features an integrated Pol Aux relay PCB as well
as status LEDs for diagnostic purposes; a Mini USB port for software uploads and service serial port for Bluetooth
connection.
The motion platform PCB houses 5 sensors. Two solid state MEM sensors which are used as the antennas horizon
reference (level position) and long term stabilization reference, and 3 solid state rate sensors, one for each axis, which are
used for short term stabilization reference. A faulty sensor on the motion platform PCB will cause the antenna to lose
stability and mispoint from the satellite under dynamic conditions; however the system may appear to be operational in
the port when there is no motion to counteract.
RS‐422 Pedestal communications from the DAC‐2202 are modulated into a frequency by the base 400MHz modem and
diplexed with the L‐Band receive signal. The communications frequency will then be demodulated by the pedestal
400MHz modem and converted back into RS‐422 before being sent to the PCU. Radio MandC signals (RS‐232, RS‐422, or
RS‐485) can also be multiplexed along with the pedestal communications to interface with the SSPB.
The 150W, 24VDC power supply is switch mode and will convert either 110VAC or 220VAC into 24VDC. This component
is universally used in the DAC‐2202, XX97 and XX06 pedestal power supplies as well as the XX09 and XX10 PCU's and
NJRC 24V BUC power supplies, meaning only a single unit is needed as a spare to cover a wide range of applications.
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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.
Document No
137738 Rev A
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