How To Change Pa Transistor; Pa Circuit - Furuno FS-1503 Service Manual

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.
Front Panel
R69 0.22Ω
Q4/5 BIAS: 40 to 60 mV
Collector bias of Q4 and Q5 measured across R69, 0.22 ohm is 40 to 60 mA normally.
SW REG
PA/FIL Board
(05P0667)
(FIL circuit)
DRIVE
Q4

(PA circuit)

PA IN
Q5
U3
PA BIAS
R39
Q6/7 BIAS Adj.: 500 mA ± 50 mA measured at FL3
Figure 5-5 PA Circuit
5-11
PA
FL3
Q6
T4
Q7
K1
PA BIAS measurement
(Cut copper foil)
FL3
–
+
DC current
meter
500 mA ± 50 mA