Comb (Fs-5075) - Furuno FS-1575 Service Manual

7. COMB (FS-5075)

This test menu is used to conduct the COMB board tests in the 4 MHz band.
The "COMB" tests are conducted with "TX IF signal: 36 kHz" outputted from CODEC,
mode set to "J2B," power data set according to the model of the system in use, and
output power of approximately 20 W. The COMB board is determined to be OK when
the detected level of the "VR PA" signals of both PA-1 and PA-2 boards is not higher
than a specified level.
The detected level can be checked by selecting [MENU] -> 9.SERVICE -> 3.RT
SETUP -> 1.SETUP -> 2.SELF CHECK -> "PA -> VR" or "COMB UNBALANCE."
The I/O: input/output impedance of the PA and COMB boards is 50 ohms. If the COMB
and PA boards cause a mismatch in their I/O impedance, for example, due to burnout,
wire disconnection, or short circuit in the COMB board, this will result in an error in
input impedance to increase the reflected voltage of VR PA, allowing for making an
acceptance judgment of the COMB board. If the COMB board test results in NG, the PA
check will definitely result in "NG.."
Furthermore, the TX, DRV, and PA boards are set to transmission "ON," and the TX FIL
board output is terminated with the 50 ohm dummy load.
RF IN 1
RF IN 2
CONFIDENTIAL (internal use only)
This confidential document is used only by FURUNO authorized persons.
It is strictly prohibited to reproduce the document in whole or in part without prior written permission of FURUNO.
CR1
T3
T4
COMB
Fig. 6.1.12 COMB Board Block Diagram
6-13
UN_BAL
T1, T2
R1
25 ohm
140W
RF OUT
6.1 [MENU] -> TEST