Furuno FAR-2107 Series Service Manual page 274

Transmission HV Protection Circuit
For instance, if the transmission high voltage 500 V for 25 kW type is used with 12 kW TR
unit, the protection circuit is activated to stop transmission.
High voltage is detected in TX high voltage input circuit on the MD board by dividing the
resistnace. The transmission high voltage detected in this way is compared with U22. If the
TX high voltage is higher than the specified value, TX triggers are stopped.
R40
X-band 12 kW TR unit: 39 kohm
X-band 25 kW TR unit: 18 kohm
S-band 30 kW TR unit: 18 kohm
Note:
1. TX pulse waveform differs depending on the setting of [Menu] -> 0 -> 4 -> 6:MODEL.
Though this is not related to the operation of protection circuit, be sure to check the
MODEL setting.
2. To check TX high voltage on the TR unit side, set [MENU] -> 0 -> 3-> 5:ANT SW to
OFF and stop antenna rotaion. Then, execute a check.
3. The detected TX high voltage is inputted to U19 (CPU) and this value is used for "HV"
indication on the self-test display. The self-test is executed by [Menu] -> 9 -> 8 -> 2 ->
2.
R1, 2
Tx-HV
R3, 4
R40
MD p.c.b
RFC p.c.b
(03P9346)
U4, 5
Fig. 4.14.2 Transmission HV Protection Circuit
4.14 Change of Transmission HV setting: HV-9017
Mag.
Q1-4
From RFC p.c.b
TRIG 1-4
TRIG 1-4
(03P9244)
R75
TX-HV PROTCT
R76
Compareter
R74
-
TX-HV INHBIT N
U22
+
R77
REF 2P5
4-71
RF TXD/RXD
Including HV
DATA/ADD. monitor signal
To MD p.c.b
TRIG 1-4