If the phone is stuck in regular recovery mode (cable logo), try booting it into (black screen) before starting the flash in 3uTools.
Move from a USB 3.0 (blue) port to a USB 2.0 (black/grey) port, as some older iDevices have compatibility issues with USB 3.0 drivers during DFU restores. 2. Repair Apple Mobile Device Drivers
The "link" aspect of this error strongly points to physical disconnection. 3utools error unable to restore idevice75 link
The USB port or cable drops below target voltage levels mid-transfer.
The following solutions are arranged from the most basic checks to more advanced troubleshooting. It's best to try them in order. If the phone is stuck in regular recovery
Download the firmware manually from a trusted site like IPSW.me . In 3uTools, click Import to select this file instead of letting the program download it automatically.
The -75 error is relatively vague but commonly stems from the following issues: Repair Apple Mobile Device Drivers The "link" aspect
Here is a step-by-step guide to resolving this error.
Standard phone chargers pass data, but a recovery stream requires unbroken power and maximum bandwidth.
: Close iTunes completely or check the "Close iTunes" box in the bottom-left of 3uTools to prevent communication conflicts.