Why does my MacBook not turn on after teardown?

My new MacBook sustained relatively minor water damage (raindrops). Afterwards it worked just fine except that it wouldn't charge (charger LED did not even turn on). The problem was identified as corrosion in the DC-in board and (with iFixit's help) I was able to remove the logic board, replace the DC-in, and put everything back together. The problem now, ironically, is that it won't turn on at all. Strangely, the charger LED shows that the charging system is now working (amber for a while, then green) so the original problem seems fixed but it won't turn on. I'm perfectly willing to believe I broke something but most of the work in removing and replacing the logic board is more subtle stuff (bluetooth connector, speaker connector, etc) and shouldn't affect basic power delivery. I've double checked that the battery connector was correctly re-seated ... what else? Is it possible there's some kind of reset required when the battery has completely drained, which it did?