Furuno FELCOM 12 Service Manual page 74

Send Level NG
Send level is calculated based on the current on the power supply line to the antenna unit.
The current detector R51 locates at the output of the rectifier on the SW REG board. The
signal detected by R51 is sent to U8, Q55 and Q51, and output to the CPU board as ANT
CUR signal. On the CPU board, the ANT CUR signal is A/D-converted by U71 and
delivered to CPU2 U23.
Transmission sequences:
The HPA ON signal generated by CPU2 U23 is sent to the PIO U13 and then the voltage
controller Q52/U10 through U54 and U57 on the SW REG board. The voltage controller
selects +29V for transmission, resulting that the current on Q51 increases and Q56 goes
on to turn on the fun. The send level is more than 123, normally the maximum 255. If the
level is less than 123, TX circuit in the antenna unit or the SW REG board may be
defective.
Power trans
(T1)
IN
U8 •F RC9083
SW REG
(16P0149)
CPU2
(U23)
Voltage control
Rectifier
(Q52/U10)
R52 R51
(0.05Ħ)
5V
Q55
Q51
Q56
ANT VOL
ANT CUR
AGC LEV
A/D
TX LEV
(U71)
HPA ON
PIO
(U13)
+ 18V (RX)
J3-1
or + 29V (TX)
R61
J4-6 ANT VOL
R62
J4-5
Q57 Q54
J4-8
J4-7 ANT CUR
J5-2 FAN
FAN
12V
J5-2
J9-7
J9-6
J9-8
CPU
(16P0148)
6-6
Antenna unit
HPA ON