Line of first rule out the horn and waiting for the circuit fault. pmSservice manual download site
 pmSservice manual download site
Key tone to the audio, if there is the sound and no voice call is usually the headphones circuit fault, focusing on startup circuit. If the connection button sound all have no, with an oscilloscope waveform measurement U205 5 feet and 7 feet (when press the button with the oscilloscope measurement), the author in the maintenance of the machine, most of the receiver is no sound U205 7 feet no waveform, the reason is the mainboard break line (as shown). U205 resistance of 7 feet R237 in to the headphone socket V406 below break line. Then good.pmSservice manual download site