Blank Screen after DC in Power Board Replacement

I have a mid-2012 macbook pro that was working fine except that the magsafe had to be wiggled to charge and it would really heat up sometimes. The power board was looking pretty beat up. So I bought a new DC in Power Board (made by Apple - identical to the old one) and replaced it per https://www.youtube.com/watch?v=hGHov4t3.... When I booted up, I would get the chime, keyboard would light, but blank screen. Apple logo on outside cover does not light and shining a light thru it does not show my login, so I conclude the backlight does not work. Tried NVRAM/PRAM and SMC resets multiple times w/out success. Tried closing the cover for a while and reopening it w/out success. Removed cover and redid all the connections and checked the cables w/ a magnifying glass to check for damage w/out success. Even replaced the original DC in Power Board and triple checked all connections w/out success. Also tried to hook up an external monitor but no success. Any ideas? Thanks.