Damn .. i should have opened it up myself too .. I had the same issue as you, sent mine back to Onkyo HK for repairs .. Unit was sent back during Jan 2020, received my phone back in July 2020 ... 6 months of delay due to the chaos and Covid ...
Can you tell me who you contacted at Onkyo? What email or phone number? The Aliexpress seller did not send the battery and I still need to get a battery for my DP-CMX1.