Gennadiy, i've used
this guide to succesfully resuscitate a couple of Audiences and a hap ac2.
Match the netinstall version to the firmware you want to revert to and, if ac3 doesn't show up, try another version - I had a situation like yours, where netinstall version opened would not see the device but I tried with another version, an older one, and all went smooth.
You can find older release
here.