Furuno GP-90 Service Manual page 17

Symptom: Fails to power
Flow 1
Supply voltage?
10.2 to 31.2 V
Blown fuse?
No
Power switch is
normal?
Open - circuit between #19 and
#20 of J9
Power on with J2
disconnected
Neither +5 V nor +12 V on J2
Vo of U8 is
+9 V?
9 V
Defective power supply
circuit on NP Board
<10.2 V
Yes
Short - circuit between #19
and #20 of J9
+5 V and +12 V is normal
on J2
0 V
GND line is equal potential to negative
power supply line.
14
Defective power supply
Wrong polarity
Defective power switch
1) GN - 8091 Board is defective, if the unit is
powered on with GN - 8091 disconnected
2) LCD unit is defective, if the unit is powered
on with J10 on the NP Board disconnected
3) MPU on the NP Board is not running if
CR7 is not blinking
Defective regulator U8 (PQ09RA1)
Top view of U8
#4 #3 #2 #1
Power on/off Vin
At power-off 24V
At power-on 24V
(Measured with 24 V power supply)
4. Troubleshooting
#1 : Vin
#2 : Vo
#3 : GND
#4 : Vc
Vo Vc
0V 0V
7V 16V