Screen flickering only when in certain submenus

[stf]

I'm using this screen: https://www.amazon.co.uk/gp/product/B00 ... UTF8&psc=1
With a wire from the second pin of the CHMC chip to the red wire. I'm using it on an external power supply, 12V.
The image is good, no flickering whatsoever when starting up, but as soon as I select a console (any of them), the screen switches off, then on, then off again many times and never gets stable (I can see AV1 showing on top right corner). As soon as I press START or B to exit the menu, the flickering stops.
The screen has been used by another user previously: http://www.sudomod.com/forum/viewtopic. ... t=90#p3054
Makes me think of an issue with automatic switch off when no source is available as this is advertised on the screen's box.
Maybe this will sound familiar to anyone?

[stf]

I'm answering my question myself - the issue came from the fact that both TV 1 and 2 were plugged, while 5V being sent to the screen by the pi. Only TV1 should be plugged in that configuration.