; Lv.
Point Service Technique
Troubleshooting Power Amplifiers
After Removing Power Transistors
In t h e supplement to T U N I N G F O R K , "Troubleshooting
P o w e r A m p l i f i e r s " , issued in 1984 we discussed several
troubleshooting m e t h o d s . Here we will discuss the check
ing m e t h o d of driver stage and preceding stages of main
amplifiers by removing power transistors and heat sinks
which occupy large space. The method varies with the type
of circuit. Fig. 1 shows three typical circuits of power am
plifiers.
Driver stage Power stage
Driver stage Power stage
Output
Output
(a)
(b)
Driver stage Power stage
+B
Output
Fig. 1 Typical Amplifier Circuits
C h e c k i n g m e t h o d
1. Circuits (a) and (b) (Fig. 1 Typical Amplifier
Circuit)
Amplifiers employing the circuit (a) or (b) can also be
checked by keeping power transistors removed. O u t p u t
power becomes 1W or less when the emitter resistors on
the driver stage are m o r e t h a n 200 Q .
2. Circuit (c)
In this circuit, output signal is unobtainable when power
transistors are removed because driver stage is not connect
ed to the o u t p u t terminal. There are two ways to obtain
the signal from the o u t p u t .
21
- B
+ B
- B
- B
( 0