The second-generation Amazon Echo Dot features dedicated up and down volume buttons, replacing the original twist-top volume control.
Here's a closeup of the 3.5mm analog audio output to the left, and the microUSB power input to the right.
Removing the rubber foot and screws lets you separate the top and bottom halves and remove the speaker.
A ribbon cable interconnects the two system PCBs.
Here's a closeup of the microUSB power and 3.5mm analog audio output connectors.
Here's a view of one side of the lower PCB in the metal assembly that houses it. The only IC of note is a Texas Instruments digital-to-analog converter, labeled 'DAC 32031 TI 68K D29G', presumably intended to drive the speaker and therefore, I suspect, also integrating a class D amplifier.
The opposite side of the lower PCB is more interesting with 1×1 Wi-Fi and Bluetooth antennas embedded within the PCB (note the odd hand-written black-ink '2' on top of one of them). In the upper left quadrant is MediaTek's MT6323 power management IC. And dominating the lower half of the PCB is a large metal shield.
Removing the shield reveals a Micron 6PA98 JWB30 multi-chip package of 4 GBytes of EMMC-interface MLC flash memory and 4 Gbits of mobile LPDDR3 SDRAM (left), MediaTek's MT8163 quad-core application processor (center), and MediaTek's MT6625 (right), which manages Wi-Fi, Bluetooth, FM, and GPS functions.
In the center of the mic PCB is one of the MEMS microphones; six other MEMS mics are concentrically arranged around the PCB edge, with 12 RGB LEDs alongside them.
In each corner of the center MEMS mic is a Texas Instruments two-channel analog to digital converter labeled 'ADC 3101 TI 681 AE4X' (four ADCs total, corresponding to the seven microphones' outputs plus a spare unused input channel). And in the lower right corner is a mysterious IC labeled R3018, which is believed to handle overall topside PCB management duties; top-side button-press detection, LED control, multi-ADC output merge and transfer to the other PCB via the ribbon cable, etc.
The four PCB-mounted switches, corresponding to the four up-top buttons, are obvious to the naked eye.
Less obvious is IC U3, alongside the 'action' switch, which appears to be an ambient light sensor that modulates the LEDs' output intensity.