Motorola Moto X Pure Edition Troubleshooting Manuals page 69

Top Earpiece and Speaker Circuit
- Inspect the physical placement of U6404 and its related components on main
PCB. (See schematic in the previous slides)
- Verify that B_PLUS voltage is present on the LS_BOOST node, the junction of
C6421 and C6424.
- Connect an 8Ω speaker to the contacts on M4670 with short, thick wires. While
playing audio at normal to high volume, use an oscilloscope to verify that the
voltage on the VBST_LEFT_AMP node, the junction of C6423 and C6425,
alternates between B_PLUS voltage and approximately 9 V, depending on the
audio content.
- While playing media audio at normal to high volume, probe the voltage across
C6422. A 384 kHz PWM waveform should be observed, similar to the example
shown below. The waveform amplitude should vary between 2 x B_PLUS up to 18
V p-p depending on the audio content.
MOTOROLA CONFIDENTIAL
Moto X Pure Edition/Moto X Style
Baseband TROUBLESHOOTING GUIDES