Chosen Solution

After replacing the keyboard and battery, a1990 does not show signs of life and does not respond to turning on or charging. I tried:

  1. Reset SMC & NVRAM - no signs of life.
  2. I tried to restore a1990 using MB16m1 DFU- a message appeared on “Cannot Use ThunderBolt Accessory”, on MB16m1, but a1990 did not switch to the DFU mode. Any ideas what’s going on? Is it possible to consider “Cannot Use ThunderBolt Accessory” a sign of life and performance a1990? Will a1990 run on mains with the battery disconnected?

Strip it again and check you haven’t pulled a board connector. Solder connections can sometimes break if handled incorrectly. You might need a microscope. Or the parts you fitted aren’t compatible.