The best use of a DSL-2750u J1 today is OpenWrt + Repeater mode . Use it to give Wi-Fi to a shed or garage. As a primary modem, it is E-waste. As a secondary tool, it is gold.

For the hardware version J1 , there is no single published "white paper." Instead, critical information regarding its firmware is documented across technical release notes and security advisories. Firmware Identification & Access

As official D-Link support wanes, use these sources:

Before proceeding, confirm you have the correct model.

The J1 hardware revision is distinct from its predecessors (like the T1 or U1 versions), and flashing the wrong firmware can turn your router into a paperweight.