Furuno 1622 Service Manual page 10

2.4!Functions of Each Circuit board
While the target scanning system of the radar uses the method of R#$ coordinates, LCD
display of this radar employs the method of X-Y coordinates, which is similar to so called TV-
sweep method.
The sweep time of the LCD display is independent of that of the radar scanning system, so
VRAM U116 is provided as the interface between them.
In order to write the radar echo signal received after every transmission trigger on VRAM U116,
CPU converts the antenna bearing signal $ into the values of SIN$ and COS$ and send
them to U118. U118 further converts them to X-Y coordinates of RSIN$ and
RCOS$. These values are used as the address to write the radar video signal on VRAM U116.
VRAM U116 also holds the past video signal for display for a trail time specified by the panel
operation.
According to the settings of the operating panel, CPU writes on VRAM U113 the display data
such as the fixed range rings, EBL, VRM, cursor, guard alarm range, and scale of azimuth angle.
Further, CPU also writes on VRAM U113 the character and numbers to be displayed on the
screen. For writing these data, GDC U112 is used.
The data writing/reading onto/from the VRAM is carried out by U118 in time-sharing method.
The display data are read out from VRAM and sent to LCD display using GDC U112.
The signals for controlling scanner unit (including the transceiver) are converted to RS-422 serial
signals in U119 and sent through a balanced RS-422 cable so that the signals may not be affected
by external noise. The control signals include those for switching the transmission on/off,
adjusting the transmitting pulse width and IF amplifier gain, and adjusting STC.
The information from the navigational aid is received through U114 and U126 to be displayed on
the radar screen.
The unit requires power supply source ranging 10.2 to 31.2 V DC. This voltage meets the
voltage requirement for ships: 10% lower and 30% higher than 12V/24V ship's mains. This DC
power is supplied through noise filters, L1, and L2, to the pulse-width-controlled DC-DC
converter mainly consisting of U6, Q6, and T1, which generates the stable voltages of +5 V, +12
V, -6V, and -22 V that are needed in display unit. The voltage +5 V is mainly used for the digital
circuits, +12 V and -6 V are used for the video and other analog circuits, and –22 V is for the
LCD display. The DC-AC inverter consisting of Q52, Q53, and T2 generates AC 210 V which is
used for the backlighting of the LCD display.
If the power supply is reverse-connected to the radar, the reverse-polarity protector activates so
that the circuit breaker is tripped or fuse is blown off to prevent the damage to the unit.
The power supply circuit contains low- and high-input voltage protectors.
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