Furuno FAR-28x7 Series Operator's Manual page 235

Problem
Marks, indications and
noise appear but no echo
(Transmission leak
representing own ship
position is absent)
Picture not updated or
picture freeze-up
Incorrect orientation of
picture
Cannot operate radar from
on-screen boxes
Radar is properly tuned but
poor sensitivity
Range changed but radar
picture not changing
(Continued on next page)
Advanced troubleshooting (con't)
Probable causes or check
points
1) TX fuse
2) Magnetron
3) Modulator board
4) SPU board
1) Bearing signal generator
board (in antenna unit)
2) SPU board
3) Video freeze-up
1) SPU board
2) Gyro interface
SPU Board
1) Deteriorated magnetron
2) Detuned MIC
3) Dirt on radiator face
4) Water ingress to the
waveguide or other
feeder line
5) Second trace echo
rejection is ON
1) Defective range key
2) SPU board
3) Video freeze-up
6. MAINTENANCE, TROUBLESHOOTING
Remedy
1) If fuse is blown, replace it. If it blows
again, the modulator or associated
circuit may be defective.
2) Check magnetron current.
Replace magnetron.
3) Replace modulator board.
4) Replace SPU board.
1) Check the connection of signal
cables.
2) Replace SPU board.
3) Turn off and on the radar.
1) The message GYRO appears when
the heading pulse is not received
during standby.
2) Replace the gyro interface.
Replace SPU Board.
1) With the radar transmitting on 48 nm
range, check magnetron current.
If current is below normal, magnetron
may be defective. Replace it.
2) Check MIC detecting current. If it is
below normal value, MIC may have
become detuned. MIC must be
tuned.
3) Clean the radiator surface.
4) Remove water from the feeder line.
5) Disable the second-trace echo
rejector referring to paragraph 1.37.
1) Try to hit RANGE [+] and [-] keys
several times. If unsuccessful,
replacement of keypad may be
required.
2) Replace SPU board.
3) Turn off and on radar.
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