lorielawrence , Find below 1st link, a guide to show how to disassemble your Game Pad to replace mother board and a couple links to where you can purchase replacement part, which you can also do a search on for better pricing perhaps. Good luck.
I hope this helped you out, if so let me know by pressing the helpful button.
[guide|57150]
http://www.ebay.com/itm/Replacement-Motherboard-Mainboard-for-Nintendo-Wii-U-GamePad-Controller-WUP-010-/112050618036
https://www.aliexpress.com/wholesale?catId=0&initiative_id=SB_20170313160950&SearchText=Nintendo+Wii+U+GamePad+motherboard