Hi, we have a Yale FB30 series forklift here.
it have started making problem when switching on the key, display just beeps with message OFF OPERATOR. occationally it works the operator says.
we seem to have lost our operations manual and service manual. also on the internet, we have not been able to find any hint on how to troubleshoot this.

Tech data:
YALE Modell FB30PZ
serial:B882R07154N

any help is appreciated.
Thank you