my mum has a Henderson marathon 550sl electric garage door.power going to main unit-plug checked to be ok.-but no response on manual override switch or on transmitter-which had a new battery fitted yesterday.serial no. of the actual unit housing the pcb`s is m5l-3015575-dont know if this helps.the door can be opened by other members of the family but not by mum as the door is far too heavy-manually.has anyone any idea?

silverfox, November 2011