No response from elrs receiver despite confirmed bind - Pixhawk 2.4.8 + Radio Master Pocket + Xr1 receiver

General
1

Hey, Everyone Newbie here building my first f450 quadcopter i am have the following issue.

Hardware:

  • Flight controller: Pixhawk 2.4.8 (clone)

  • Firmware: ArduCopter V4.6.3 (92b0cd78), ChibiOS

  • Frame: F450 QUAD/X

  • TX: RadioMaster Pocket, internal ELRS module, flashed to 3.5.2 via web flasher (full chip erase, ISM2400, binding phrase set)

  • RX: RadioMaster XR1 Nano dual-band ELRS receiver — originally shipped on firmware 3.5.2-pr3035 (pre-release build), later OTA-flashed via WiFi to 3.5.2 matching binding phrase

Symptoms:

  • XR1 LED goes solid blue (bound) after binding

  • Pocket Lua script shows “Telemetry connected” intermittently

  • RSSI in Mission Planner stays at 0

  • Radio Calibration shows zero channel movement

  • “PreArm: RC not found” message persists (except briefly disappeared once when testing a different SERIAL port, but data still wasn’t flowing)

What I’ve already checked/tried:

  • Wiring confirmed crossed correctly (FC TX → RX TX, FC RX → RX TX), verified multiple times

  • Tested on three separate UARTs: TELEM1, TELEM2, and SERIAL4/5 — same result on all three

  • SERIALx_PROTOCOL = 23, SERIALx_BAUD = 115 set correctly matching whichever port is wired

  • RC_OPTIONS = 8704 (bits 9 + 13 set, for ELRS 420k baud + suppress rate mismatch)

  • RC_PROTOCOLS = 0 (all enabled)

  • RSSI_TYPE = 3 (ReceiverProtocol)

  • BRD_SBUS_OUT = 0

  • Multimeter check: XR1 5V pin reads 4.9V (healthy), XR1 TX pin reads ~3.29V idle (expected UART idle high)

  • Full chip erase + reflash done on both Pocket TX and XR1 RX, matching binding phrase set on both, matching firmware version 3.5.2 confirmed on both

Question:
Given a confirmed RF bind (solid LED) but zero RC data reaching the FC across three different UARTs with correct protocol/baud/RC_OPTIONS — what else should I check? Is this consistent with any known issue related to the receiver previously running a pr3035 nightly build? Could a partial/incomplete OTA flash leave residual config that a WiFi-based update doesn’t fully clear (since WiFi OTA can’t do a full chip erase)? Any guidance on confirming CRSF output directly from the receiver without a logic analyzer would help too.