Recently my uRADMonitor A3 WiFi unit stopped connecting to the network. The device would power up but was unable to establish a WiFi connection. The symptom, 3 beeps and no hotspot.

My initial suspicion was that the ESP-04 WiFi module had failed, so I began searching for replacement modules and placed an order for new parts. While waiting for them to arrive, I decided to investigate further with some guidance from @uradmonitor.

My first step was attempting to reflow the ESP-04 board without any luck. Afterwards, I decided to try to determine where the fault was on the ESP. Using my oscilloscope, I probed the TX and RX, the clock and I could see activity at startup and then nothing. The next step was to read the SPI flash contents from the ESP module. I was able to successfully extract the firmware image, which suggested that the flash memory and at least part of the ESP hardware were still functioning correctly. My plan had been to try to swap the flash from a donor board (ESP-03) had I not been able to find an ESP-04 board as they appear to be hard to find.

Since there was no visible component damage, I decided to try once again reflowing the ESP module and surrounding solder joints once more. I had already performed one reflow attempt earlier without success, but I figured it was worth trying again before replacing any parts.

This time, I was very generous with the flux, and surprisingly, the second reflow solved the problem. After powering the unit back on, it connected normally and returned to reporting data online.

In the end, the root cause appears to have been a poor solder connection rather than a failed ESP module. No parts needed to be replaced, and the unit has been operating normally since the repair.

This experience was a good reminder that intermittent solder joints can sometimes mimic component failures, especially in devices that have been operating for many years.

The repaired unit is running firmware:

sw124 (type:8 hw:103 ws:124 SI29BG)

and is now back online and reporting data normally.

The ESP-04 shows no signs of any issue prior to the relow: