Ipad pro 12.9 no power after screen replacement :(

Hi can't seem to find much information on the ipad pro repairs?

swapped a screen on ipad pro 12.9 (2nd ipad pro 1st no probs.

followed all of the usual steps and took great care in my workshop as usual however I now have no power and no response when plugged into iTunes.

i have tried to disconnect battery for 30 mins or so.

checked all soldering and connections second part still nothing.

can't find schematics or any info anywhere. customer device :(

thanks in advance.