GS728TP v1 failed update

The image shared on ibb.com with the 2x5 pins reminds me more to a JTAG port. J2 with the notch on the 5x2 Dupont connector -might- be intended for plugging a RS-232 DB9 COM header cable designed for the mainboards with 2.0 mm pitch header pins. AT resp. Everex pinout.

• 5x2 Dupont connector, 2.0mm pitch
• AT/Everex pinout

I'd expect to find a an unpopulated 4-pin UART serial header on the motherboard (usually labelled as JP1, J3, or CONSOLE (wild guessing, JP1 or J1 most likely) near the main Broadcom SoC or flash memory).

The 4-Pin Internal Pinout

Netgear is highly consistent across their smart switch and router lines with their 4-pin internal layout. On the PCB, look for the square solder pad or the small arrow/number indicating Pin 1.

The standard pinout configuration runs as follows:

Critical Connection Guidelines

• Voltage Warning (TTL Levels): This header operates at 3.3V TTL logic levels, not RS232 levels. Connecting a standard 12V RS232 serial cable or DB9 adapter directly to these pins will permanently fry the switch's motherboard. You must use a USB-to-TTL adapter (such as an FTDI, CP2102, or PL2303 chip breakout board) configured to 3.3V mode.
• Leave VCC Disconnected: Never connect Pin 1 (VCC) to your USB-to-TTL adapter. The switch is already powered by its internal power supply. Connecting the adapter's 3.3V or 5V power line to this pin risks creating a voltage conflict that can damage both the switch and your computer's USB port.
• The RX/TX Cross: When wiring your USB-to-TTL adapter to the board, remember that the signals must cross over:
  • Adapter GND $\rightarrow$ Switch GND (Pin 4)
  • Adapter TX $\rightarrow$ Switch RX (Pin 2)
  • Adapter RX $\rightarrow$ Switch TX (Pin 3)

Serial Terminal Settings

Once connected, open your preferred terminal emulator (PuTTY, Tera Term, Minicom) and configure your COM port to the following standard Netgear settings:

• Baud Rate: 115200 (Some older revisions of the GS728T use 9600, but 115200 is standard for modern firmware bootloaders)
• Data Bits: 8
• Parity: None
• Stop Bits: 1
• Flow Control: None

If you power on the switch while connected, you should instantly see the U-Boot or CFE bootloader decompression text scrolling across your screen.