Audio Systems: jvc no audio help!, rca jacks, internal speakers

Question
i have two jvc projection sets model av-56wp74 with no audio.internal speakers are turned on & center channel input is turned off.audio is not muted.there is no audio from rca jacks & using a signal tracer i can find no audio anywhere.i believe both sets have identical problem as swapping citcuit boards between sets still produces no audio.i have 40 years experience repairing consumer electronics but these dogs have me stumped.i have service manual but cannot pinpoint where audio originates.

Answer
SAP Off?  

These are analog sets you know, you will get no service from antenna signal.

Also, check the noise muting function as if it is turned on it can kill the audio  (owners manual page 41).

And, check, if you haven't already, for dc voltages at the audio output stages.  Sometimes a regulator in the main power supply will fail that feeds the audio section.  If there are dc voltages appropriate to the operation of the amps, then inject a test signal right at the input of the power module/amp and see if you are getting speaker output.  If not, check with scope right on the output of the amps at the heatsink area.  Far fetched but could speaker wires out of the amp be broken or open (or a hidden link fuse?)...

Let me know; sounds like a weird one!  cleggsan at cleggsan dot com