If your computer or box flags a short circuit immediately after connection, use a multimeter to check the resistance between GND and your signal lines. If a line reads 0 ohms, your solder point has bridged to a nearby component. If you(e.g., UFI , EasyJtag Plus , Medusa ) What error message are you seeing in your software log?

Connect a USB cable from the PC to the phone's Type-C port to provide the required VCC/VCCQ operating voltages. Common Use Cases for the STK-L21 ISP Interface Problem Scenario Solution via ISP

: A fine-tipped soldering iron (preferably T12 or JBC style with a 0.1mm tip) and high-quality leaded solder flux.

If you chose the USB trick for power, plug the Type-C cable into the phone. Click or Check eMMC .

Always verify the PCB revision on your board. The pinout above works for:

Detailed visual guides and pinout diagrams for this specific model can be found on professional GSM forums and technical sites: Diagrams & Guides