59
SC-LX81
5
6
7
8
5
6
7
8
A
B
C
D
E
F
[5] Power Amp Section Troubleshooting
In the speaker output, the sinusoidal wave of about 430k - 4
8
0 kHz 2
V
rms (when immediately after the current is applied with no
signal/no load; the switching frequency varies by the connected load, signal level and the energizing time) is always output.
It is the switching waveform (±64
V
square wave) in the output stage that has been attenuated through LPF.
If such remained waveform can be observed, it can be assumed that the amplifier is operating normally.
W
hen a signal is input to the amplifier, the output signal of the speaker shows the waveform such that the remained switching waveform
is superimposed onto the audio signal.
N
ote that when the input signal level is extremely small, it may not be easy to confirm the audio
element since it is buried in the remained switching waveform (approximately 2
V
rms).
W
hen no sound is produced with a specific function or sound mode, it is not caused by a failure in the power amplifier block.
W
hen
there is a failure in the power amplifier block, no sound is produced with every function.
It is recommended to set the speaker setting to "LARGE" for all the channels and the function to "MULTI CH I
N
" when examining the
power amplifier.
Amplifier Diagnosis with Current Applied (1)
N
o
Yes
Is the energization
state maintained?
If the protection circuit shuts it down immediately,
perform
Amplifier Diagnosis without Current Applied
.
N
o
Yes
Check the path (cables and connectors) of
AMUTE and SBMUTE.
Check again whether the audio signal is
not output in the speaker output even if
the input signal level is increased.
Confirm that the input signal comes to C
N
6
8
00,
the input connector of ICE BUFFER Assy.
Perform
Amplifier Diagnosis
with Current Applied (2)
N
o
Yes
Yes
Does the
speaker output shows
the remained switching waveform?
(Sinusoidal wave of
about 430k - 4
8
0kHz,
2
V
rms)
N
o
Is the
speaker relay on?
(Confirm the relay operation noise
using the SPEAKER button
within the front door)
Check the relay power supply ±12
V
(pins 5 and 6 of C
N
4903), relay control
signal (pins 9 - 12 of C
N
4000) and the
path (cables and connectors).
N
o
Yes
Yes
N
o
Check the ±12
V
path (such as connectors).
Does the input
signal come to the input of
ICEPO
W
ER AMP Assy? (Ex. the
pin 6 (FLch) of C
N
3
8
20 and the
pin 1 (Cch) of C
N
3
8
10 of
ICE I
N
TERFACE
Assy)
Is the
ICE BUFFER Assy OPAMP
power ±12
V
supplied? (C
N
6
8
10
and C
N
6
8
20 of ICE BUFFER Assy, power
is supplied separately to each channel.
(Ex. Pin 7 (-12
V
) and pin
8
(+12
V
) of C
N
6
8
20
for FLch)
Is the MUTE disabled?
(Are the pins 5 and 6 of C
N
4000
of ICEPO
W
ER AMP
Assy set to H?)
