In message , Robin
writes
On 26/02/2021 08:40, Ian Jackson wrote:

snip

One way of finding out if an RC is actually transmitting a signal is
to hold it close to a radio with a ferrite rod aerial, and tuned to a
quiet spot on the long wave. If the RC is transmitting, you will hear
a 'burpity-burp' noise when you press the a button.

How does that detect a failure of an infrared transmitter?

It won't tell you if the actual LED has failed (which is unlikely), but
it will give you pretty good confidence that the rest is OK. As Brian
has said, for the LED, some digital cameras might show you it's flashing
(even if it's not visible to the human eye).
--
Ian