Thank you for the very helpful comment - I was facing the same issue!
The card identified in the pictures is not a combined Wi-Fi / Cellular card. It is just a 3G cellular card; the WiFi card is the other card tucked under the flat ribbon next to the card pictured in this guide
It could be the AC power adapter is not functioning correctly. You may want to double check the charging port, too. (Samsung Chromebook Series 3 Charging Port Replacement)
Some creative placement helps: lay keyboard flat (ribbons up), fold chromebook hinge to 90 and lay on its side slightly overlapping the keyboard: this should gives the ribbons enough slack while giving us visibility and room for hands. Don’t forget to close the little “locks” on each side of the wide ribbon.
For me, in this step, all the screws were T5.