Troubleshooting Driver Amplifier & Bias Network Circuits; Protection Light Will Not Go Off After Replacing Output Transistors - Sony STR-DE845 Training Manual

Troubleshooting Driver Amplifier & Bias Network Circuits

Protection light will not go off after replacing Output transistors

Most modern Power Amplifiers use an IC package for the Drive Amplifier (shown in Figure 11-1). If you have
small DC offset voltages at the Driver amplifier output, the protection circuit will be triggered and the receiver will
enter the protection mode. In this case, change the Driver amplifier IC. If that does not solve the problem, check
the positive and negative power supplies to the Driver amplifier IC. Sometimes there are switching networks in
the B+ and B- paths to the Driver amplifier IC. These switching networks are used to limit the gain of the Driver
amplifier.
NOTE: Small offset voltages on multiple channels are usually caused by bad ground connections (troubleshoot
for open ground trace or traces).
C601
R601
10
1
50V
IN
+
C602
100
INPUT
1
NF
2
3
4
-VEOUT 5
+VEOUT 6
R4
V55
7
GNO
8
D2
D1
VCC
9
R9
IC601
STK350-230
1 2 3 4 5
C606
R604 68
C604
C605
47
+
16V
FIGURE 11-1 - PROTECTION MODE
11. Troubleshooting Driver Amplifier & Bias Network Circuits
IC601 STK350-230
TR3
TR1
TR2
TR4
TR7
TR5
R3
R8
R7
R5
TR8
6 7 8 9
(+)
(-)
NETWORK
FB
39
R1
R2
R5
TR8
D3
D4
(+)
BIAS
FB
(-)
OUTPUT
11.1A124
OUT
T
RE
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