Hello everybody.
Some time ago I made a homebrew PCB to take a VGA output from this board. I believe that the logic inverters schematics is more efficient compared with the discrete transistors based like it was in the A20-OlinuXino-MICRO.
There is a drawing of this shield, maybe it will be useful for someone: https://yadi.sk/i/4rXUP2E23KG6zL (https://yadi.sk/i/4rXUP2E23KG6zL)
There are gerbers of the shield: https://yadi.sk/d/D0rCo_u63KG7i2 (https://yadi.sk/d/D0rCo_u63KG7i2) Keep in mind that position of connectors XS1 and XS2 is critical. Also it's important to have inverter with T index because of it's 3.3V logic compatibility (74ACT series, but 74HCT must be fine as well).
Some photo of the result:
(http://www.picshare.ru/uploads/170619/3uSyOsJ4gP_thumb.jpg) (http://www.picshare.ru/view/8143033/) (http://www.picshare.ru/uploads/170619/2KDh1B2Ai0_thumb.jpg) (http://www.picshare.ru/view/8143036/) (http://www.picshare.ru/uploads/170619/1ALDxvKi0t_thumb.jpg) (http://www.picshare.ru/view/8143039/)
And about my question: I noticed the VGA picture is slightly overexposed, so to speak. This is most noticeable in the light areas of the image:
(http://www.picshare.ru/uploads/170619/PK41E26A1M_thumb.jpg) (http://www.picshare.ru/view/8143043/) (http://www.picshare.ru/uploads/170619/1E1PG93LzP_thumb.jpg) (http://www.picshare.ru/view/8143044/)
It looks like the RAMDAC was not turned properly. I beleive it must be some software for the A20 SoC that can make a gamma correction and change other image parameters. Do you know anything about this?