Furuno 1622 Service Manual page 11

2.4!Functions of Each Circuit board
2.4.2 Scanner Unit
INT Board (03P9271)
INT board contains: one-chip CPU U3, that includes the RAM, ROM, and analog ports; U5
including I/O ports the stepping motor drive circuits; and U7 including the A/D converter which
outputs tuning, gain, and STC control signals.
The output from U7 is used to control the STC and gain of the IF amplifier and the frequency of
microwave local oscillator for MIC.
The operating conditions of the radar that have been set on the operating panel of the display unit
are sent to the CPU U3 on the INT board through the RS422 communication line. The CPU U3
controls the stepping motor drive circuit U5 which drives the stepping motor to rotate the
antenna. The antenna azimuth signal is created in the stepping motor drive circuit and mixed
with the heading signal (S801), and sent to the display unit.
In order to change the transmitting radar pulse length according to the selected range, the pulse
width information is sent from the INT board to the modulation circuit on the MD board.
There are the automatic mode and manual mode to adjust the gain of the IF amplifier. In the
automatic mode, CPU U3 monitors the video signal from the IF amplifier, and the monitored
signal inputs to the A/D converter U7 through the I/O port U5, and the A/D converter output
controls the IF amplifier gain. In the manual mode, the signal set by manual setting inputs to the
A/D converter, and the A/D converter output controls the gain of the IF amplifier.
This radar employs an automatic tuning system in which the main bang signal from the IF
amplifier is amplified and inputs to CPU U3 as the signal indicating the tuning level.
The CPU U3 controls the output of the A/D converter U7 so that the tuning indication level may
become maximum.
The adjustment of STC is also carried out in the same way as the gain adjustment.
IF Amplifier Board (03P9269)
The IF amplifier, the intermediate frequency of 60 MHz and band width of 7 MHz, consists of
Q1, U1, U2, and a buffer Q4. This board includes the gain and STC control circuits consisting of
Q2 and Q3. Another circuit, consisting of Q5 to Q10, detects the main bangs to indicate the
tuning level.
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