Is it possible to turn the a500 display off when connecting to a TV using HDMI out? If you try to lock the device (hit the power button), it halts the device completely. There is not brightness option for "completely off," so that's not an option. Ideally, I'd like to save battery if I'm watching a movie via HDMI. Does this require a 3rd party app, if so, do you know of any? Thanks in advance!