Chosen Solution
No boot sound and no sound when in OS (10.14.3). System Preferences shows that the internal speaker is there. I can plug in headphones and the output source changes to headphones and sound does play through them. I’ve replaced the speaker, I/O Board, and cable that connects I/O Board to logic board. I’ve tried resetting SMC and PRAM. I’ve booted to a live Linux USB and sound doesn’t work there either. I’ve run out of ideas besides replacing Logic board and/or CPU riser board. Thanks for the help.
Did you replace the Port board? It has the DAC chip (Cirrus) on the same side as the speaker. I’m suspecting the one of the trace lines going to it from the speaker is your problem. Check the solder joints on the chip and the surrounding area. Trace the speaker connection to the DAC
