Furuno FS-1503 - 5.5 How to Change PA Transistor

5-11
5.5 How to Change PA Transistor
CAUTION: Apply a thin coating of silicone grease to transistor 2SC3240. The
grease aids the transfer of heat from the transistor to the chassis. Before wiring,
transistor must be fixed to the chassis securely.
The PA bias must be checked after replacing the PA transistor.
1. Disconnect "PA IN" connector.
2. Make a open circuit on FL3 and connect a DC current meter.
3. While pressing the PTT switch down, adjust R39, PA BIAS so that the meter reads
450 to 550 mA.
SW REG
PA/FIL Boar
d
(05P0667)
Front Panel
K1
T4
FL3
PA BIAS
(FIL circuit)
(PA circuit)
Q
6
Q
7
Q
4
Q
5
U3
R69 0.22Ω
Q4/5 BIAS: 40 to 60 mV
Q6/7 BIAS Adj.: 500 mA ± 50 mA measured at FL3
R39
PADRIVE
PA BIAS measurement
(Cut copper foil)
DC current
meter
+
–
FL3
500 mA ± 50 mA
PA IN
Figure 5-5 PA Circuit
Collector bias of Q4 and Q5 measured across R69, 0.22 ohm is 40 to 60 mA normally.