Scantronic 9100 will not reset?

I have a similar alarm with a similar problem having opened the front panel to inspect the battery (I have the engineer's code). After doing so, the expected command (i.e. zero enter/engineer's code/99 enter) to restore "day mode" does not work. Only the "power" LED is showing. Does this mean a full reset involving the NVM chip as advised elsewhere on this Forum? Any ideas avoiding this would be much appreciated.

Romo1947
July 2020

zero enter 99 then your code

Paddy
February 2010

Wow one of my most favourite panels ever, Steve you need to let me know what leds are showing on the keypad ao that i can help.
Regards
Nick 07842 480037

Nick
January 2010