Sanwa MT4 not “transmitting”

[Ashlandchris]

Hi all.
Odd thing happened today. All was working well then suddenly my transmitter seems to have stopped transmitting. Powers fine, battery charged etc (eg obvious things checked) but car is as though not connected.
I have 5 models set up so popped a battery in spare car and tried another. Nothing
I tried rebinding. Nothing
I reset the model on the TX. Nothing
I tried to bind to an empty channel. Nothing
When Tx turned on I can see the screen reaction to turning the wheel or throttle, but Rx not receiving anything.
I noticed the “signal” indicator on screen is not there (I compared it to my daughters MT4 and saw that had the antenna signal thing (like an old Nokia phone))
Any suggestions? Is it kaput?