Sorry I couldn't help. My RG350m and 280m only turn off the screen when I'm already in the main menu.
BTW, it might just be an issue with some of Anbernic's screens, but one time I left the screen off on my 350m for an extended period of time, and it looked completely washed out when I turned it back on. It's happened to other people, and the display seems to always recover fully, but I avoid turning off the display at all while the device is powered, just in case. I mentioned the issue in my "open handhelds" thread.
If I didn't already have two JZ4770 handhelds I'd be all over the 351m. The 351v looks great as well. Not top-heavy like some of the vertical devices.
The v doesn't have wifi built in, right? Have you tried going online with it? If so, are you able to update the cores from within Retroarch, like you can on computer and android releases?
I like how you can
set this generation of devices up to launch directly into Retroarch, or whatever else, but I'm going to try to sit out Rockchip. Anbernic can't seem to stop putting these things out, and I'll jump back in as soon as they release something that will perform on the same level as the Tegra 4 (Shield Handheld) without burning your hands or requiring active cooling.