Furuno 1835 Operator's Manual page 110

6. MAINTENANCE, TROUBLESHOOTING
Problem
Radar is correctly
tuned but sensitivi-
ty is poor.
Range changed
but radar picture
does not change.
Range rings are
not displayed.
6-6
Probable cause or
check points
1) [2nd Echo Rejector] is [On]
2) Dirt on radiator face
3) Deteriorated magnetron
4) Detuned MIC
1) RANGE key has faults
2) SPU board
3) Video freeze-up
1) Adjust their brilliance on the
[Brill/Color] menu.
2) SPU Board
Remedy
1) Turn off the [2nd Echo Re-
jector], from the [Echo]
menu.
2) Clean radiator.
3) Check the magnetron cur-
rent with the radar transmit-
ting on 48 nm range. If the
current is below normal,
magnetron may be defec-
tive. Replace the magne-
tron.
4) Check MIC detecting cur-
rent. If MIC detecting cur-
rent is below normal value,
MIC may have become de-
tuned.
1) Try to operate the RANGE
key. If you can not operate
the RANGE key, replace
the keypad.
2) Replace SPU board.
3) Turn off and on radar.
1) Replace associated circuit
board if unsuccessful.
2) Replace SPU Board.