I have a strange situation that occurs. Every now and then, the Shure MPA-3C does not operate correctly with my iPhone. It is like the iPhone is ignoring or mis-interpretting the MPA-3C output. Sometimes I can restore the MPA-3C functions by doing a "hard reset" of the iPhone software. A friend recommended that I restore the firmware on the iPhone. Do you think it is the MPA-3C or the iPhone?
Sorry to say, but it is likely the iPhone's software or firmware. The MPA-3C is a simple device. It provides a switch closure which is interpretted by the iPhone software. The following link describes the functioning of the MPA-3C:
The following link describes problems from lint/dirt being in the connecting jack/plug:
The function of the MPA-3C can be checked by trying it with a different iPhone, or checking it with an ohmmeter, or send it to Shure Service for examination/repair. However, if the MPA-3C operates OK at times, it is very likely that the problem lies within the iPhone software/firmware.