LSQuad Serial port
From NAS-Central Buffalo - The Linkstation Wiki
As with many linkstation models, there is a pinout for a serial connection, but not all of the pinouts are connected. To make a serial connection, we must jump some traces on the board, add a header, and connect with a serial TTL/Level shifter, most easily with the Nokia CA-42.
On the LSQuad (LS-QL/R5), the pinout is located at the lower front side of the board. Looking at the inside/processor side of the board, the pinout is on the lower right. The rightmost pinout (#1) is the ground. Going leftwards, #2 is the +3.3V, skip that pin. #3 and #4 will be the TxD and RxD.
Solder in the header first, extending to the outside (non-processor side) of the board. Remember the clearance with the case, you may need to bend the header pins 45 or 90 degrees up to connect once the board is re-installed.
Then jumper a lead that goes from the back (processor side) of the pin #3 to the small hole just to the left of R147.
Add another lead that goes from the back of pin #4 to the righter-most of the two holes above and between C47 and C53. You'll see the the more leftwards of the two holes is the terminus of the trace the extends from R147.