Adjusting the output voltages from the power supply modules
If you need to adjust the output voltages from a power supply module, this must be done while measuring the voltage on the TRXU Terminal block in the Transceiver Unit. This is necessary because you need to compensate for any voltage drop in the power cables.
Prerequisites
Two people are required to do this task.
The MS70 is switched on and working in normal operational mode.
You must be equipped with a standard set of tools. This tool set must comprise the normal tools for electronic testing, as well as the necessary tools for relevant disassembly/assembly for test access. Each tool must be provided in various sizes. We recommend that all tools are demagnetized to protect your equipment.
You need the following test equipment:
•  Multimeter
WARNING
High voltages are used. This equipment must only be serviced by qualified personnel familiar with the construction and the operation of the MS70, as well as the potential hazards involved. Failure to observe this precaution could result in bodily injury.
Context
The outputs from the three power supply modules are connected to the terminal block on the left cabinet wall. The output from the +75 VDC power supply is fed through an NTC resistor. In order to filter out voltage variations caused by noise or load variations, large capacitors are connected to each of the +12 VDC and +6 VDC supplies. These capacitors are physically located in the three TRXU subracks in the Transceiver Unit.
The DC cables from each of the three Power Supply Units to the Transceiver Unit are all separate conductors in a bundle. 230 Vac is also included in order to power the fans in each TRXU subrack.
Inside the Transceiver Unit, the power cables are terminated in three TRXU Terminal blocks, one for each subrack. From these terminal blocks, the three DC cable bundles are fed up to the rear side of the subrack, and terminated with plugs on the Power Connector Panel.
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Each TRXU Terminal block is used to make the connections between the Power Supply Unit and the relevant subrack in the Transceiver Unit. The cables from each Power Supply Unit are connected to the top of the terminal block. Connections are then made to the Amphenol plugs that match the Power Connector Panel.
The AC power provided by the Power Supply Units is also terminated on the Power Connector Panel.
The following cables are included in the bundle:
•  230 VAC to TRXU subrack fans
•  +6 VDC (two red cables)
•  -6 VDC (two blue cables)
•  +12 VDC (one red cable)
•  -12 VDC (one blue cable)
•  +75 VDC (one red and one blue cable)
Note
If you need to adjust the supply power output voltages while the MS70 is turned off, make the measurements on the terminal block on the left side of the Power Supply Unit.
Procedure
1 Open the Power Supply Unit.
2 Open the rear door on the Transceiver Unit.
3 Observe the terminal blocks on the left side of the cabinet.
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4 Do one of the following steps
a Measure the individual voltages while the MS70 is turned off.
Measure the voltages on the terminal block in each Power Supply Unit. Verify that the voltages are approximately:
•  +6 VDC (Approximately)
•  +12 VDC (Approximately)
•  +75 VDC (Approximately)
b Measure the individual voltages while the MS70 is operating normally.
Measure the voltages on the terminal blocks in the Transceiver Unit. Verify that the voltages are:
•  +6.30 VDC ± 0.1 VDC
•  +12.0 VDC ± 0.1 VDC
•  +75.0 VDC ± 0.1 VDC
5 Adjust the relevant output voltage using a short screwdriver on the adjustment screw.
6 Close the Power Supply Unit.
7 Close the rear door on the Transceiver Unit.