Thanks RogerA1, I rang and got the correct email address (support@logicrc.com - but had a reply from spektrum@logicrc.com) with the following reply:

Hi Eric

I would say with out seeing the radio it’s a main board issue the issue there is if it is the boards are no longer available so would be unable to fix.
You are welcome to send in the radio for investigation

Regards
John Norris
Logic RC
www.logicrc.com

That’s that then! Being sold for spare or repairs!
Thank you all..
Eric

Logic RC phone number correction I missed a 5 from the number should read 01992 558226

Hi Eric
Sorry missed a 5Number is 01992 558226

Thanks all for the really helpful suggestions, particularly the link to Logic RC - RogerA1, could you check the telephone number you listed please? Looks like there’s a number missing..

Logic are the UK appointed horizon hobby service centre, great service, very fair prices

That is good information Roger - a good UK service centre for Spectrum is just what we need - thanks for the "heads-up'.👍

Bob.

I have an old 6I which had problems with the digital Trims
Spektrum repairs had been transferred to Germany.
I found a repair company in Hertford called Logic RC Ltd
They were absolutely brilliant fast service and very reasonable price. Tel 01992 58226

Rechargeable batteries hav a lower output voltage than alkaline, even right coming off the charger. A lot of electronic devices were designed to use alkaline and then the hobbyist thinking he/she will save $$$ by using rechargeable, will substitute nicads and learn the hard way. Also, rechargeable hav no where near the ampere-hour capacity of an alkaline

I have just done an AI on your question and it has come up with this-🤔🙄

An older Spektrum DX6i that fails to retain settings (like servo reverse) and reverts to model 1 is
likely suffering from a failed internal memory capacitor, corrupted memory, or, most commonly, severely degraded battery power/contacts. The transmitter cannot save data because its internal power is too low to maintain settings when the main batteries are turned off.
Immediate Troubleshooting Steps:
Check Battery Voltage: Ensure your AA batteries are fully charged and putting out adequate voltage. Low batteries frequently cause memory loss in older DX6i units.
Clean Battery Contacts: HeliFreak users recommend cleaning the battery contacts and checking the tension of the spring clips in the battery tray to ensure a tight connection.
Check "Back" to Main Screen: When making changes, always return to the main screen (where the model name and voltage appear) before turning off the transmitter. Turning it off while in a menu can prevent saving.
Perform a Factory Reset: Model Boat Mayhem suggests holding the sticks down and outward while powering on the transmitter to trigger a factory reset. You can also go to Setup List -> Copy/Reset -> Reset.
Replace Transmitter Batteries: If you are using rechargeable AA batteries, they may be old and not holding a charge under load. Try a brand-new set of alkaline batteries.
If these steps do not fix the issue, the internal non-volatile memory or the component responsible for holding settings is likely dead, which usually requires a repair from "Horizon Hobby" or replacing the transmitter.
Hope this gives you something more to try, Steve..🙄

Register on Spectrum’s web site. This will allow you to download updates and apply them to your transmitter.
This may fix your issue