Furuno 1715 Service Manual page 9

1.2 Display unit
The unit operates on universal voltage ranging from 10.8 V to 31.2 V DC. This range covers the
voltage requirement for 12 V/24 V ship's mains 10 % lower and 30 % higher. The ship's mains is
supplied through a noise filter to the pulsewidth-controlled DC-DC converter which generates
the stable voltages; +5 V, +12 V, +8 V and –24 V. The ship's mains is also supplied to the
scanner unit, bypassing the power supply circuit in the display unit. +5 V is mainly used for the
digital circuits, +12 V for the video circuits, +8 V for the backlight, and –24 V for the LCD
display. The DC-AC inverter consisting of Q33, Q34 and T1 generates 210 V AC for the
backlighting of the LCD display.
If the power supply is connected to the radar in reverse polarity, the reverse-polarity protector
activates so that the fuse is blown off to prevent the damage to the unit.
The power supply circuit contains low- and high-input voltage protector.
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