I installed a RepRapDiscount FULL GRAPHIC Smart Controller on my Geeetech A10M.
but i had a screen with back light but no info displayed.

If i shorted pins 18 and 19 briefly to test contrast, i got info on the display but contrast was too much.

I modified the contrast circuit buy adding 5v to contrast pot. This needed to solder a link, cut a track and remove contrast pot and rotate anti-clockwise.

see photos for details.

12864 Display frame is to go between LCD and main PCB to stop them being squeezed together. Need to just to make thingiverse happy because you cant upload unless you have an model.