Sorry can't help, but I've a similar problem having just had to re-fix the legs on one. The thing fell over as I was fitting it back together and two wires came loose from on of the two the connectors which are attached to the on off switch. A black and a white. Any idea where they go?
I found Mountfield most unhelpful, unwilling to provide a circuit diagramme.
howtomendit.com for free repair help, information and advice.
Try fixfault.com to fix chainsaws.