Furuno GP-90 Service Manual page 15

If GPS selftest detects an error, it is indicated by an error code listed in table 4.4.
Errors
ROM Error
RAM Error
BACK UP MEMORY Error
RTC (Real Time Clock) Error
ROM Error and RAM Error
ROM Error and BACK UP
MEMORY Error
ROM Error and RTC Error
RAM Error and BACK UP
MEMORY Error
Table 4.5 lists an error vs. defective parts.
No.
1 ROM Error
2 SRAM Error
3 BACK UP MEMORY Error
4 RTC Error
Table 4.4 GPS selftest error codes
Error
codes
03 RAM Error and RTC Error
04 BACK UP MEMORY Error and RTC Error
ROM Error, RAM Error and BACK UP
10
MEMORY Error
20 ROM Error, RAM Error and RTC Error
ROM Error, BACK UP MEMORY Error and
07
RTC Error
RAM Error, BACK UP MEMORY Error and
13
RTC Error
ROM Error, RAM Error, BACK UP
23
MEMORY Error and RTC Error
Discontinuity of cable between GN-8091
14
and NP Board.
Table 4.5
Error
12
Errors
Faulty Parts
U4
U5
BT1, CR3, and surrounding
circuit on NP Board
U1
4. Troubleshooting
Error
codes
24
30
17
27
33
34
37
FF