The two screws in step 24 are different.
One is indeed a 1,5mm (the one on the left in the picture (Seen from bellow)). The other is a 1.0 mm? (I don't have a caliper on hand).
The important part of this is that the 1,0mm? won't fasten in the socket to the left! - it's just not long enough to catch the grooves... which could result in a loose power button.