Kone escalator fault codes

Has anyone got fault codes for a kone travel master escalator? Its spitting out error code 50 but I can't find what it means.

Thanks guys

My list says "Safety Chain Interrupted", The input is X1/12

I have missing start signal. Lost key off position input but did not get a direction input or after key turned back to center did not see off input for 10 seconds. I think a bad key switch is a good possibility.

You were spot on mate, found that the top key switch was buggered. Thanks for answering. Proud to be part of a good group of guys.