Sharp LC-90LE657U Service Manual page 63

Is the audio output from the monitor set at "VARIABLE" or "FIXED" on the menu screen?
YES
Are there the audio signal outputs at pins (AN34) (HP_MONITOR_L) and (AN35) (HP_MONITOR_R) of IC3301 (CPU)?
YES
Does the audio signal come from pins (2) (MONI_HP_L) and (11) (MONI_HP_R) of IC1702 (Line-out Amplifier) to pins (3) (L) and (2) (R) of J504?
YES
Check the connector (J504) and their peripheral circuits, and speakers and the Cable.
Does the signal come to 1pin of LAN-jack J9401?
(see fig-1, fig-2)
Does the signal come to AT18 pin of IC3301?
(see fig-2)
Check IC3301 and its peripheral circuits.
fig-1
No monitor audio output
Check IC3301 (CPU) and its peripheral circuits.
Check IC3301 (CPU) and its peripheral circuits.
Check the line between IC1702 and J504 and their peripheral circuits.
Check the LINE_MUTE line and its peripheral circuits(Q506/Q510, etc).
No connect network
YES
YES
LAN-jack J9501
1pin
NO
NO
NO
NO Check the interface device and peripheral circuits.
(power-LED of hub, LINK-LED of hub)
NO Check the line between J9401 and IC3301.
Check the LAN-jack J9401.
fig-2
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LC-90LE657U