MBP 2015 A1398 820-00138 audio problem

[MicroSMD Lab]

Hello group, there is no sound from the internal speakers and it does not show up as a device, when I plug in a headphone, headphone does show up but all i hear is a recurring pop. The digital audio output gets activated.
PP3V3_S0_AUDIO_ANALOG is 20ohm to gnd and PP4V6_AUDIO_ANALOG is 4.3ohm to gnd. Are these resistances ok, is voltage injection safe on these lines? Thanks in advance.

[mon2]

Re: MBP 2015 A1398 820-00138 audio problem

What are the voltage measurements of these power rails?

They do sound (no pun) low to me. Do not do injection yet.

[MicroSMD Lab]

Re: MBP 2015 A1398 820-00138 audio problem

PP3V3_S0_AUDIO_ANALOG is 3.3V and PP4V6_AUDIO_ANALOG is 1.7V
4V5_REG_IN is 4.9V

[mon2]

Re: MBP 2015 A1398 820-00138 audio problem

I don't have the schematics in front of me but locate all caps on this rail PP4V6_AUDIO_ANALOG.

Start with the largest and carefully remove off the pcb or slide to one pad only. Then check the resistance of that rail again. Some part, likely a cap is shorted. The voltage should not be this low. Often the bad players are polarized tantalum capacitors.

[reformatt]

Re: MBP 2015 A1398 820-00138 audio problem

U6200 (TPS71745) is only rated to 150ma max. 4 ohms will exceed that (V=IR). There are only 4 caps on this line and U6201 to isolate what is causing it.

[MicroSMD Lab]

Re: MBP 2015 A1398 820-00138 audio problem

Thanks for the responses mon2 and reformatt. I removed all 5 capacitors and U6200 but no change in resistance... removed the U6201 and short is gone