when you took the LCD out the iPad are you sure you didn't damage it? there is adhesive on the back of the LCD which without being heated up properly it can cause the LCD to break? if you can lift the digitiser up without breaking, you can inspect the LCD? There is a small, bottom right which sometimes comes loose, try popping that back in? Also it could be another short circuit, maybe a component damaged on the logic board? hope this helps.
Have you tried checking settings to see if fast charge is enabled? Sounds stupid but i found that to happen once or twice on mine. also you could purchase a USB voltage detector online which are a few quid, and see the voltage going in to the phone? Hope this helps.