Yes, this is yet-another-amp-not-detected post, sorry for this.
I've got my Amp+ in April, installed, configured, all worked fine with volumio.
Then as it happened, I didn't use the assembled device for half a year. A couple of days ago I tried it again — it didn't even start. Took it out of the case, took the Amp+ off. Pi works. Put Amp+ back again — volumio loads fine, but Amp+ is not detected. Upgraded to the latest kernel. Tried raspbian from your download pages. Always same, dmesg says
snd-hifiberry-amp sound: ASoC: CPU DAI (null) not registered
snd-hifiberry-amp sound: snd_soc_register_card() failed: -517
platform sound: Driver snd-hifiberry-amp requests probe deferral
tas5713 1-001b: ASoC: failed to probe component -5
snd-hifiberry-amp sound: ASoC: failed to instantiate card -5
snd-hifiberry-amp sound: snd_soc_register_card() failed: -5
snd-hifiberry-amp: probe of sound failed with error -5
with the 3.18 kernel, or
snd-hifiberry-amp soc:sound: ASoC: CPU DAI (null) not registered
snd-hifiberry-amp soc:sound: snd_soc_register_card() failed: -517
snd-hifiberry-amp soc:sound: ASoC: CODEC DAI tas5713-hifi not registered
snd-hifiberry-amp soc:sound: snd_soc_register_card() failed: -517
tas5713 1-001b: ASoC: failed to probe component -110
snd-hifiberry-amp soc:sound: ASoC: failed to instantiate card -110
snd-hifiberry-amp soc:sound: snd_soc_register_card() failed: -110
snd-hifiberry-amp: probe of soc:sound failed with error -110
with 4.4.30. Either way, only "bcm2835 ALSA" device is found, amp+ isn't.
Sometimes it doesn't even start at all — both red and green leds stay on and nothing happens. Removing Amp+, booting pi once on and off, putting Amp+ back — that helps to make it start again.
