With custom code, the standard i2C-Scanner sees the MPR121 touch sensor chip at the right address but the TouchTest (in the MPR121 examples) reports that it is not communicating. [The chords work but the harp is silent.] Any suggestions on what components to look at?
[That MPR121 has such a fine pin pitch (no pun intended). Our soldering did not go so well, but it looks OK under a microscope and even X-Ray’d.]