Help identifying K1P Z4 transistor
Googling SOT23 marking K1P the first hit links to the MMBT2222 datasheet
which contains the following text ( on page 2 in a section called"Marking Information" ). 


  K1P = Product Type Marking Code
  YM = Date Code Marking


and a further table decoding the "ym" date code. The table only goes up to W (=2009) but it's reasonable to guess that Z4 means April 2012.

Seems pretty conclusive to me.
(SOT23 is an industry standard packaging which looks exactly like those in the photo)

And it's a common type of NPN switching transistor so it should be very easy to find a replacement or a suitable substitute.