MacBook Pro A1708 No sound/audio, sound card is not showing up in the system repair

Problem description
When A1708 is not playing audio and the audio device is not showing up in the system

Symptoms

 * No audio out
 * Sound card not showing up in the system

Solution
It could be a chipped off R2041 on the backside of the CPU, so no AUD_PWR_EN on L6361 and therefore only 0.3 V on L83_1V8 for the U6300 chip. Installed new resistor and sound card shows up.

You may want to check these four main ICs responsible for sound on the 820-00840/00875 boards U6200/6300/6400/6420. Compare diode mode reading with known good board in regard to these ICs. Also refer to schematic and check VIN, enables, data lines (U6400/6420 AUD_I2C_SDA/ AUD_I2C_SCL) etc. Check values of all resistors associated with these four ICs (refer to schematic for values)