Pioneer SC-LX81 Service Manual page 59

5
[5] Power Amp Section Troubleshooting
In the speaker output, the sinusoidal wave of about 430k - 480 kHz 2Vrms (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 (±64V 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.
When 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. Note 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 2Vrms).
When no sound is produced with a specific function or sound mode, it is not caused by a failure in the power amplifier block. When
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 IN" when examining the
power amplifier.
Amplifier Diagnosis with Current Applied (1)
Is the energization
state maintained?
Yes
Does the
speaker output shows
the remained switching waveform?
(Sinusoidal wave of
about 430k - 480kHz,
2Vrms)
Yes
Does the input
signal come to the input of
ICEPOWER AMP Assy? (Ex. the
pin 6 (FLch) of CN3820 and the
pin 1 (Cch) of CN3810 of
ICE INTERFACE
Assy)
Yes
Is the MUTE disabled?
(Are the pins 5 and 6 of CN4000
of ICEPOWER AMP
Assy set to H?)
Yes
Check again whether the audio signal is
not output in the speaker output even if
the input signal level is increased.
5
6
No
If the protection circuit shuts it down immediately,
perform Amplifier Diagnosis without Current Applied.
Is the
speaker relay on?
No
(Confirm the relay operation noise
using the SPEAKER button
within the front door)
Yes
Perform Amplifier Diagnosis
with Current Applied (2)
Is the
ICE BUFFER Assy OPAMP
power ±12V supplied? (CN6810
No
and CN6820 of ICE BUFFER Assy, power
is supplied separately to each channel.
(Ex. Pin 7 (-12V) and pin8
(+12V) of CN6820
for FLch)
Yes
Confirm that the input signal comes to CN6800,
the input connector of ICE BUFFER Assy.
No
Check the path (cables and connectors) of
AMUTE and SBMUTE.
SC-LX81
6
7
Check the relay power supply ±12V
No
(pins 5 and 6 of CN4903), relay control
signal (pins 9 - 12 of CN4000) and the
path (cables and connectors).
No
Check the ±12V path (such as connectors).
7
8
A
B
C
D
E
F
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