How to enter service menu, thanks to fakefaketington:
There's also a submenu called Tool option 1.* Power off the monitor (soft power-off is fine).
* Press left-left-left-right *while off* (this is the only "magic sequence" bit).
* Press the middle "select" button to power on as normal.
* When the display is on as normal, press the "select" button then press right like you want to enter normal "Menu", but its now tied to the service menu until the next power cycle.
* To exit the service menu, scroll to the blank (no option is selected/colored), and press "select".
I created new thread, because I want it to be indexed by search engines and will be easily googled.