I'd first try changing resolution or refresh rate.
The exact labels used will differ depending on which firmware you have on your device.
In general, click on a settings icon if you have one. If not, open the list of all currently installed Android applications, and scroll until you find Settings, and click on it.
If you have a black background, then look for entries titled Screen and/or Display. Now look for HDMI mode. If the resolution/refresh rate are set to auto, turn that off. Now change the mode to something different. If NOTHING appears on your screen, don't click anything on your remote, and the device will revert to your previous settings. If you can see a message asking if you want to keep this new mode, confirm you do. Not check if the picture pulses off and on. Repeat for each mode you can select until you find one that your LG is happy to display.
If you have a colourful settings screen, head to the last tab and click on the More or Advanced Settings button, then follow the steps in the previous paragraph.
Thank you for testing on a different TV by the way, that has helped to speed this process up!
