[russellb]

Well, some developments, probably not very positive.

I went over the Rx board and reheated most, if not all of the solder joints, as some looked marginal
No change on reloading the software, so I decided to check voltages, and found that while the 9v and 5v lines were OK, the 3.3v was showing only 1.4v
I took C5 out to check it wasn't short circuiting, and on reconnecting the voltage is now only 0.44v. I've hunted carefully for solder bridges, and no signs.

I presume this means that IC3 is cooked? I had noticed it hot earlier. Is it practicable to replace it? I can get an AMS1117-3.3v for $1,
From the 3.3v line to ground measures about 250 ohms. Does that sound reasonable? It would represent a current of about 130 mA which seems fair.
It certainly doesn't seem there is a major short circuit dragging the voltage down.

The absence (for practical purposes) of 3.3v would explain the wi-fi not starting, and I presume the BME280 and RTC would also fail,and hence the software would not run?

FWIW the 3.3v terminal on the Arduino board produces 3.3V.

Regards

Russell