Thanks for that. Interesting what you find by minor variations in search words; I’d already turned up various threads about sine waves etc, which didn’t seem useful as I have a KW transformer, which definitely appears in the list in the manual.
However I’ve now turned up this https://ogrforum.ogaugerr.com/...-will-not-exit-reset , which seems a good description of the problem. Batteries are cheap, so I’ll try a new 9v alkali and see what develops.