The failure mode on the Quattro’s that I’ve had problems with is very odd. Walking, talking, chewing, loud noise all seem to reactivate external mic input but the mic input dies away if I’m just sitting around. All the failed Quattro’s I’ve had, too, worked fine just after booting but die away just sitting around. Jostling the HA body or the receiver wire reactivates the mic, too. Streaming is always stellar, even on a failed device.
One thing that I’ve noticed is that all Quattro’s but my latest left replacement have somehow accumulated gunk internally. When one looks at the bottom of the HA body at the clear plastic window over the internal serial number, on all previous Quattro’s, the inside of the window has accumulated debris like very fine dandruff, dust, dirt, obscuring the serial number. So I’ve also been wondering if as originally manufactured, the Quattro’s don’t have high enough dirt resistance (the IP rating is 58) whereas the Ones have an IP 68 rating as do the Marvels and the Paradises as well. So if dust and dirt had anything to do with the problems I’ve experienced, I’m not sure why walking, talking chewing, and other movements reactivate the sound. Sweat-induced corrosion has been mentioned as a possibility in the past but in the last two years, especially with the pandemic, I haven’t been doing any real sweating and don’t wear the devices outdoors when it’s hot out in Texas.