Serial connection can receive but can not send

Issue: When connected via serial to my device and booting up, I can receive data, but I can not send anything, i.e. no keyboard input possible during boot process.

Root causes:

1. Faulty serial adapter
2. No physical connection between the RX serial pin/pad on the board and the CPU
   • intended by the OEM (resistor or jumper not soldered)
   • unintended by user (bad soldering of pins/wires, lose plug contact, pcb trace cut/delaminated, …)

Solutions:

1. Open putty and test serial adapter by connecting RX and TX
   • If what you type on the keyboard is echoed back to the screen → OK
   • If not → faulty serial adapter, get a new one.
2. Check the serial connection visually for continuity. In case of interruptions detected
   • Solder missing resistors/jumpers → see devicepage of your device (use the wiki search or the ToH to find the devicepage)
   • Make sure pins/wires are soldered correctly. Re-solder if necessary.
   • Repair any cut pcb traces / delaminated pads

Links:

• Serial port troubleshooting
• In case of doubts / still not working → OpenWrt forum