ARC stopped working on Onkyo NR-636

I returned home from work last night only to find my previously working home cinema setup had gone on the fritz, and after few hours of trying everything I can think of in the OSDs, I'm turning to you for help.

Setup:
LG 49-850V 4K TV
Onkyo NR-636 receiver

Previously this combo has worked fine over ARC, using HDMI 2 (ARC) socket on the TV to the main/ARC HDMI socket on the amp.

However, when I got home last night the amp had somehow switched itself to Zone 2 which gave no audio (unsurprisingly given I have no speakers connected to Zone 2).

After switching the amp back to Zone 1, I also noticed that the HDMI logo on the amp's screen was no longer showing, indicating that it wasn't syncing with the TV.

After lots of back and forth, such as disabling then renabling ARC (on both devices) I've convinced the TV's device connection menu that the Onkyo NR-636 does exist, and it now can control the volume on the AMP again (i.e. you can see the numbers on the amp going up and down), However, there still isn't actually any audio, and the amp still doesn't turn on/off when the TV does (it previously did this fine).

I suspect the amp itself is fine as switching to another source such as DVD is okay, with perfect audio and picture.

I've found a few threads online with people having similar experiences, and they fixed it by on the amp disabling ARC, exiting setup, enabling ARC, and exiting setp (which forces the amp to rescan for connections). However, this doesn't resolve the problem for me.

Forgot to ad, I've also tried reseating the HDMI cables on both devices.

Any ideas?

 

Sounds like a case for an Onkyo service engineer.

 

Have you powered at least the TV and AVR off at the mains (unplug if needed) for a few minutes, then re-powered them? {not just standby}. As advised by Onkyo in the manual, if my 515 is anything to go by, when setting up.

HDMI CEC/ARC is a black art and occasionally gives everyone grief.

Onkyo have had hdmi board issues Onkyo | Customer Care Program

 

Thanks to you both for the suggestions. This morning I did a full factory reset on the TV and the AVR but it didn't resolve the issue so after speaking to the UK Onkyo customer service team I've returned the unit to Richer Sounds for them to have a play with and if necessary return to Onkyo for repair.