Note: when headphone has no output, firstly make clear whether relay is disconnected, then test
whether SHUTDOWN pin voltage of LM4880 is normal ( 2.5V when in normal condition), and finally
judge whether headphone has trouble or LM4880 has trouble.
Example 6 Symptom: no sound output
Description: after power on, connect to 5.1CH, main channel has no output, centre and surround
have output, power board FL101, FL102 fuse is burnt down.
Analysis and troubleshooting: change FL101, FL102 fuse, power on again, fuse is burnt down,
power off, shown as in the figure 3.3.1.5, test resistence to ground of power board Vc+, Vc- and
resistance is zero ohm, unplug power board flat cable holder XS8, test resistance to ground of power
amplifier board Vc+, Vc- and it also zero, so we preliminarily judge that trouble lies on power amplifier
board. Test resistence between each pin of power pipe V112 of power amplifier board and they are all 0,
resistance between each pin of power pipe V113 is 0, V112, V113 have been stricken through, change
V112, V113, change fuse, after power on again, output is normal and trouble is removed.
[
]
Note: when a certain channel has no output, firstly make sure voltage of each channel power
amplifying circuit is normal. Generally, test stage by stage from final stage of signal output and analyse
the reasons. For voltage is unstable, power IC is easy to burn down; machine vibrates in the course of
con, which may break the line of PCB board of signal board, or make copper piece of element pin fall off.
When analysing questions, we should consider.
Example 7 Symptom: no screen display
Description: after power on, relay attracts, output signal is normal, VFD has no display.
Analysis and troubleshooting: connect to power, test voltage of panel XS10 and it is normal, change
VFD display screen, display is normal and trouble is removed.
[
]
C101
10u/16V
C103
47u/100V
C105
100u/16V
C107
47u/100V
R105
2K
R106
2K
R107 47
R108
47
V102
2N5551
V103
2N5551
V104
2N5551
VD102
1N4148
VD103
1N4148
R110
510
R109 1K
R112
1K
R116
150
R113
150
R121
33K
R111
33K/0.5W
V105
2N5401
V107
2N5551
V106
2N5551
V132
2SC5248
V112
2SC5200
V113
2SA1943
V133
2SA1964
R 114 4.7K
R115
2.2K
C108
33p/500V
C109
47n
R 117
220/0.5W
R125
220/0.5W
R120
100/0.25W
R122
100/0.25W
R126
0.25/7W
R127
0.25/7W
R104
47K
R103
1K
R102
100K
C104
220p
Vc+
Vc-
V101
S8050
R128
4.3K
R130
4.3K
R129
1.5K
C110
0.47u/16V
V114
2N5551
VD104
1N4148
R101
10K
Figure 3.3.1.5 Power amplifier circuit diagram
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