Terastation Serial console
From NAS-Central Buffalo - The Linkstation Wiki
As we can see from the hardware page, the CPU offers two serial ports. The first one is used for the system console, but it's not accessable from outside the box. The seccond one is used to communicate with the XXX microcontroller.
But there actually is a serial port on the back of the box. Officially it is used to communicate with the UPS.
If we open the box, there is the serial port in lower back corner:
Close to it is a Sipex3220EE level shifter to convert the 5v (or 3.3v) TTL-levels to RS232.
If we look closely the three, actually four, pins of the level shifter are connected to middle pin of the three connectors: JP3 (TxD), JP4 (RxD), JP5 (Vcc).
Inorder to connect the system console we must first remove the three 0Ω resistor (R437, R440, R441) and move them to (R438, R439, R442). The Rx line from the CPU is still not connected. We also have to bridge R76 to connect it. Do not remove R75, it is a 10kΩ pull-down. If you remove it the input line to the CPU will float and feed random junk to it, not what you want.
Removing the SMD resistors already is a pain, so I decided to add three pin-heads/jumper.
J1 can be used to direclty access the serial console, but it's uses 3.3v TTL levels and you need a seperate level shifter. I added some connectors, as I've a proper level shifter from some oher embedded projects.
Getting serial access to the system is essential to become root.
The crucial information came from TeraStation �?��?��?��?� - シリアルコンソール�?� SSH.