Troubleshooting Power Amplifiers After Removing Power Transistors - Pioneer tuning fork Service Manual

; Lv. Point Service Technique
Troubleshooting Power Amplifiers
After Removing Power Transistors
In the supplement to T U N I N G FORK, "Troubleshooting
Power Amplifiers", issued in 1984 we discussed several
troubleshooting methods. Here we will discuss the check­
ing method of driver stage and preceding stages of main
Driver stage
(a)
Driver stage
Fig. 1 Typical Amplifier Circuits
Power stage
Output
- B
Power stage
+B
Output
- B
( 0
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
(b)
Checking 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. Output
power becomes 1W or less when the emitter resistors on
the driver stage are more than 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 output terminal. There are two ways to obtain
the signal from the output.
Power stage
+ B
Output
- B
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