From NAS-Central Buffalo - The Linkstation Wiki

How to attach a serial port to the Kurbox/KuroboxHG

 Please note the adding of a serial port requires soldering onto the main board of the Kurobox and can cause catastrophic failure to the hardware. You have been warned 

Locate J1 on the Mainboard after removing it from the case. This will be a 4 pin unpopulated header. To allow one-way serial port traffic (read only) you can just add the 4 pin header and be done. To enable bi-directional serial port activity, you must also add a 10K resistor as described below.

Adding the serial port

J1 Pinout

1	Transmit (TX)
2	Receive (RX)
3	Power (3.3V)*
4	Ground (GND)

Adding the level shifter

The serial port signals from the processor are only 3.3V. For proper RS-232 5V signaling, an RS-232 level shifter needs to be added. These are very common in PDA seial cables also, but can be purchased from Compsys Bench

Item Name: A232DBH3v Max232 3.3v ver. adapter assembled w/hood kit 
Item Number: A232DBH3v 

This should be attached as close as possible to the board. The signals are very weak and wires as short as 2" have been reported to cause data loss across the serial port.

Once you have the level shifter installed you should be able to see console messages via the serial port. To be able to write across the serial port, follow the next steps.

Enabling Write support

To enable write support across the serial port, remove the 10K ohm pullup resistor from R75 and install it , or another 10K ohm pullup resistor, to R76.

Serial Port Settings

• 57600 Baud
• 8 Data Bits
• No Parity
• 1 Stop Bit.

Just adding the J1 header to the board is enough to see serial console information. It will not allow transmit. To provide serial port transmit support (ie sending characters) you must remove R75, a 10K ohm pullup resistor and move it to R76.