Short Pulse And V Trig Signal - Furuno FAR-2107 Series Service Manual

2. Short pulse and V TRIG signal

U1 (MB3776AP) on the MD board is a switching power supply and generates the
power supply to the trigger amplifier circuits of the RFC board (Q1 -12) and MD board
(Q5-20). The adjustment of output voltage of U1 is made at VR1 on the MD board. This
is the adjustment of Magnetron current which has been set at the factory. There is no
need for this adjustment when the Magnetron is replaced in the field. The "SHORT
PULSE" signal controlling U1 from the RFC board increases voltage and TX output at
S1 pulse. This signal also turns on K1 on the MD board to make the pulse trailing edge
steep. This is achieved by short-circuiting L1 for a certain time and reducing the
residual voltage of the Magnetron. In a similar manner, K1 and K4 are controlled at S1
and S2 pulses on the S-band radar.
3. TX PROTECT signal
TX high voltage is divided (R1/2, R3/4, R40) on the MD board, and output to the RFC
board as TX-HV protect signal. If it is higher than the TX high voltage specified in the
"MODEL" setting of the INITIALIZE menu, the RFC board stops TX triggers. This
signal is also used as monitor signals for TX high voltage.
Tx-HV
Fig. 7.2.6 Schematic diagram of TX protection circuit
Fig. 7.2.5 MD board (03P9244)
R1, 2
Q1-4
R3, 4
TRIG 1-4
TRIG 1-4
R40
MD p.c.b
(03P9244)
R75
R76
RFC p.c.b
(03P9346)
Compareter
R74
R77
REF 2P5
U4, 5
7-10
Mag.
From RFC p.c.b
TX-HV PROTCT
RF TXD/RXD
DATA/ADD.
-
TX-HV INHBIT N
U22
+
7.2 Antenna Unit
VR1
For adjustment of
Magnetron current
VR1 on the MD board
(No need for adjustment
in the field)
Including HV monitor signal
To MD p.c.b
TRIG 1-4
at