MT8127D internal HDMI 1.4 TX → [ESD array] → HDMI connector
Pin Signal Direction Connected To Used Notes
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1 TMDS_DATA2+ OUT TV HDMI port YES Differential pair — video
2 GND (TMDS2) GND Ground plane YES
3 TMDS_DATA2– OUT TV HDMI port YES
4 TMDS_DATA1+ OUT TV HDMI port YES Differential pair — video
5 GND (TMDS1) GND Ground plane YES
6 TMDS_DATA1– OUT TV HDMI port YES
7 TMDS_DATA0+ OUT TV HDMI port YES Differential pair — video
8 GND (TMDS0) GND Ground plane YES
9 TMDS_DATA0– OUT TV HDMI port YES
10 TMDS_CLK+ OUT TV HDMI port YES Pixel clock differential
11 GND (CLK) GND Ground plane YES
12 TMDS_CLK– OUT TV HDMI port YES
13 CEC BIDIR MT8127D GPIO YES HDMI-CEC for Alexa commands
14 HEAC+ / Res N/C Not connected NO Reserved in HDMI 1.4
15 DDC_SCL OUT MT8127D I²C controller YES EDID clock (100kHz)
16 DDC_SDA BIDIR MT8127D I²C controller YES EDID data
17 GND (DDC/CEC) GND Ground plane YES
18 +5V IN TV HDMI source YES Powers hot-plug detect circuit
19 HPD IN MT8127D GPIO YES Hot-plug detect → triggers EDID read
ESD note: Black component between shield and HDMI connector (visible in side photo)
is almost certainly a TVS array on pins 1–9 (TMDS lines) — standard ESD protection
practice for HDMI on compact boards.
Guess Notes: Pin 14 (HEAC+/ARC) is almost certainly not wired — no audio return
channel capability observed or documented. CEC is actively used for Amazon's HDMI-CEC
integration with Fire TV remote.
Pin Signal Direction Notes
──────────────────────────────────────────────────────
1 VBUS IN +5V from AC adapter (5V @ 1A max)
2 D– N/C Data– not connected (power-only use)
3 D+ N/C Data+ not connected (power-only use)
4 ID GND/N/C OTG ID pin — tied to GND or N/C (client mode only)
5 GND GND Power return
Guess Notes: No USB data path to host — this is power-only. ID pin handling
determines OTG capability. If tied to GND: client mode only. If floating with
pull-down resistor to MT8127D: OTG-capable in hardware (firmware may lock this).
Interface Signals Status Notes
─────────────────────────────────────────────────────────────────
HDMI 1.4 TMDS ×3 + CLK + CEC ACTIVE Full use
LPDDR3 bus 32-bit parallel (~200 pads) ACTIVE Under main shield
eMMC 5.0 8-bit parallel (CMD/CLK) ACTIVE To Toshiba NAND
USB 2.0 HS D+/D– + VBUS POWER ONLY Data pins likely N/C
PCIe (if any) N/A INACTIVE MT8127D has no PCIe
I²S audio 3–4 signals UNKNOWN No speaker output visible
I²C (DDC) SCL + SDA ACTIVE EDID only
SPI 4-pin UNKNOWN Possibly to boot ROM
UART0 TX/RX (2 test pads) LIKELY ACTIVE Standard debug console
JTAG TDI/TDO/TMS/TCK INACTIVE/N/C Likely unpopulated
GPIO Multiple MIXED LED, button, HPD
The two test pads visible near the Micro-USB connector on the top side are
almost certainly UART0 TX/RX (115200 baud, 3.3V logic level) — standard
MediaTek platform debug console. On production units these are unpopulated
(no header pins soldered) but the pads are present.
Pad 1 (likely): UART0_TXD — MT8127D serial output (listen here)
Pad 2 (likely): UART0_RXD — MT8127D serial input (send commands here)
GND: Any nearby ground pad
Baud: 115200, 8N1, 3.3V logic
Output: MediaTek preloader → LK bootloader → kernel dmesg → Android logcat
To access: Solder 0.1" header pins, connect 3.3V UART adapter (do NOT use 5V).
Screen/minicom at 115200 baud. Boot device while connected.
Authored: Albert Lane + Claude Sonnet 4.6 · SovereignAudits™ · 2026-06-10