Chosen Solution

I recently replaced my Macbook Pro’s battery. When I completed the last step, I rebooted my Macbook and everything was perfect except for the keyboard. Not one key worked - not even the power button. The only way to get it to boot has been to disconnect the battery cable and plug in the MagSafe power cord. After about 10 seconds, the laptop boots, just be virtue of the fact I’ve connected it tp AC power. Things I have tried since then: Replaced the trackpad/keyboard cableReinstalled the OS.Connected a USB wired keyboard and tried resetting the PRAM and SMC.I was successful resetting the PRAM with the wired keyboard, but have never been successful in resetting the SMC. Even on this USB keyboard, that key combo does nothing. In short, everything about the laptop is perfect and normal (and yes, the trackpad works) except for two things:

  1. If I shut it down, the only way to power it back up is by first disconnecting the battery, then plugging in the Magsafe.
  2. The built in keyboard is completely dead. I’ve combed through support forum threads for days, without success. Does anyone here have any ideas? Update (06/22/2020) Well, more fun. I successfully replaced the keyboard … and …. everything works EXCEPT for the keyboard. So, there must be something else afoot here. Any ideas? Again, here are the oddities - everything else works:
  3. If I shut it down, the only way to power it back up is by first disconnecting the battery, then plugging in the Magsafe.
  4. The built in keyboard is completely dead. The trackpad works beautifully and the keyboard backlight works. I can only use the laptop with a USB keyboard.
    Thoughts?

The SMC should reset when you disconnect the battery. Since you have replaced the keyboard cable the only other thing you can try without taking voltage and diode measurements would be a replacement keyboard.

There is one component you might have disturbed when lifting the flap on the connector. It is R5710 if that has been nudged it could cause these symptoms.