iPod Nano 6th Gen - No Screen Activity - Black Screen, Even After Digitizer/LCD Replaced - But is Otherwise Operable [Works Fine with iTunes, etc.]. Troubleshooting Help?

As mentioned in the title, I'm working with an iPod Nano 6th gen where there's nothing happening on the screen, regardless of what help method you try. It's been fully charged, remains active and responsive to iTunes [has been successfully restored, able to add/remove files, play songs, etc.], and has even had the LCD digitizer and screen completely replaced.

Regardless, there is zero screen activity going on. It remains dark [with both the original and brand new digitizer], so I'm seeking assistance on what the root cause here may be.

I'm thinking it's either the battery, as I've heard similar stories where all else was fine but a bad battery kept the screen from functioning. But I would think that having it on a live connection would allow the screen to function..... And then I think it's the logic board, but that appears to be just fine given the otherwise operable state of the device.

Any help would be greatly appreciated.

Thanks.