microphone not working in my acer aspire E5-571G-52R7 since last two month

Try running this Terminal command:

sudo echo "options snd-hda-intel model=dell-headset-multi" > /etc/modprobe.d/snd-hda-intel.conf

Then reboot and retest your mic.

If it does not work for you, please try replacing dell-headset-multi with one of the following model options:

!!! Only test ONE model option at a time between each reboot of your PC !!!

Test all audio jacks at the front and the back of your PC after each reboot.

ALC22x/23x/25x/269/27x/28x/29x (and vendor-specific ALC3xxx models)
======
  laptop-amic Laptops with analog-mic input
  laptop-dmic Laptops with digital-mic input
  alc269-dmic Enable ALC269(VA) digital mic workaround
  alc271-dmic Enable ALC271X digital mic workaround
  inv-dmic Inverted internal mic workaround
  headset-mic Indicates a combined headset (headphone+mic) jack
  headset-mode More comprehensive headset support for ALC269 & co
  headset-mode-no-hp-mic Headset mode support without headphone mic
  lenovo-dock Enables docking station I/O for some Lenovos
  hp-gpio-led GPIO LED support on HP laptops
  dell-headset-multi Headset jack, which can also be used as mic-in
  dell-headset-dock Headset jack (without mic-in), and also dock I/O
  alc283-dac-wcaps Fixups for Chromebook with ALC283
  alc283-sense-combo Combo jack sensing on ALC283
  tpt440-dock Pin configs for Lenovo Thinkpad Dock support

sudo echo "options snd-hda-intel model=dell-headset-multi" > /etc/modprobe.d/snd-hda-intel.conf

Won't work,

You need to use:

echo "options snd-hda-intel model=dell-headset-multi" | sudo tee /etc/modprobe.d/snd-hda-intel.conf

tried still not working

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