Scantronic 9800 problem?

Hi, this morning I unset my alarm (28 years old) and as I am doing some electrical work in the kitchen, I needed to switch the house power sockets off at the control box. Immediately my Scantronic activated the internal alarm with code LB (low battery) but despite entering the code it would not cease ringing. Called an engineer who changed the battery in the alarm control box but then found the keypad 'died' ie no LCD or green power on light. There is 2 amber lights showing and although the number keys buzz when pressed, there is no LCD display. Any ideas whats happened. Thanks

Michael512
June 2020