Separating main board from plastic housing... more screws! Twelve more Torx security screws and one lone Philips.

Very simple construction here, and only the one board. It's a little unfortunate that so many ports are soldered down/difficult to service—but there's so much redundancy with those nineteen accessory ports, maybe it's not a big deal? (Provided you don't need all 19 of course.) It helps that button functions can also be remapped in software.

Just a few chips in this sea of green:

A Microsoft-branded ARM chip labeled X905893-002

This is more than likely the MCU. One person claims this same chip is in the Xbox One controllers (the 1708 variety).

Texas Instruments BQ24250 2 A Li-ion battery charger w/ power-path management

FTDI Vinculum-II programmable USB 2.0 host

NXP PCAL6524 I/O expander