Furuno FAR-2107 Series Service Manual page 426

7.2.6 MSS board (MSS7497)
The MSS board is used for S-band radars and not compatibly used due to different part
by differences in antenna motor voltage.
MSS7497A
ANT motor power supply: 380/440VAC
Since the antenna size of S-band radar is large, there is a risk that the antenna revolution
mechanism and motor may be damaged due to too large loads if the rated voltage is
applied to the antenna motor suddenly. To prevent this, the antenna revolution is
generally increased without applying the rated voltage onto the motor at the time of
power-on. After rotating loads are decreased, the rated voltage is applied. At the time of
power-on, only two phases of V and W are connected to the motor to make the motor
rotate slowly. The switching circuits of Q1, 2 and 3 are controlled by voltage generated
by full-wave rectification to change the conduction angle of the remaining one phase.
- At the time of power-on:
Q3 (junction transistor) is brought into conduction after waiting for delays by the
time constant of R6 and C3 and turns on the triacs CR2 and CR13 by way of the
photo triac couplers U1 and U2. When U1 and U2 are turned on, C4 is discharged
through Q3, and Q3 is turned off.
Fig. 7.2.15 Circuit Diagram of MSS board
7-21
MSS7497
ANT motor power supply: 200/220VAC
7.2 Antenna Unit