Section Three Servicing Cases
3.3.1 Servicing cases
Example 1 Mixed left channel on AV board has no sound
Analysis and troubleshooting: Step 1: use oscillograph to test LO signal on pin 5 of XS401 on power
amplifier board and find that there is no signal, after unplugging flat cable on XS401, LO still has no
signal output, so we can confirm that trouble lies in power amplifier board.
Step 2: use multimeter to test power supply of N8 (TLV272) and it is normal.
Step 3: use oscillograph to test pin 55 and 56 of N12 (TAS5508) and find that there is digital
waveform output, so we can judge that trouble lies in the circuit between N12 (TAS5508) and XS401.
Step 4: use oscillograph to test pin 2 and pin 3 of N8 (TLV272) and find that there is waveform input,
but when testing pin 7 of N8, there is no waveform output, so we preliminarily decide that N8 has trouble,
after changing N8, trouble is removed.
Note: N12 has waveform output but it is certain to be correct, because N12 may probably only
output carrier signal but no modulating signal.
Example 2 Headphone has no sound
Analysis and troubleshooting: insert headphone and test DET signal of pin 7 of XS201 on power
amplifier board and it is low level. Use oscillograph to test pin 5, 6 of XS201 and there is no HR, HL
signal, test pin 61, 62 of TAS5508 and there is output; check power supply of N10, N11 (4580) and it is
normal; test pin 1, 7 of N10 and there is no output! So we doubt that N10 is damaged, after changing
N10, trouble is removed.
Example 3 External input has no sound
Analysis and troubleshooting: adjust DVD plauer in AV IN state, and find that there is sound when
playing disc, so we can preliminarily confirm that the common part of external input and audio output
when playing disc is normal, shown in the figure 3.3.1.1, that is, elements behind N4 are all normal, and
now we only consider N5, N7, N4 and circuit among therm. Use multimeter to test power supply of N5,
N7, N4 and it is normal, use oscillograph to test output pin of N5 pin 13 and 3) and they both have signal
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