User "Somedude" on the forums produced a rough, hand-drawn schematic of the D-808 in 2021. It focuses on the power management IC (the PMU that allows charging via USB-C) and the rotary encoder matrix.
Driven by a single 18650 lithium battery . The charging circuit is managed internally via a micro-USB (older) or USB-C (newer) port. Identifying Your Hardware Version xhdata d-808 schematic
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