The blades on this Stihl hedge trimmer were bound up and wouldn't stroke. There was no obvious debris preventing the stroke.  Accessing the gearbox revealed worn lobes on the spur gear and worn driving rings on both blades. Lack of lubrication was likely the cause.

The spur gear was replaced and an attempted repair was made on the blades. After short use. The repaired blades failed (cracked at the driven end) and replacements were installed.

Watch the video to see the repair was done on a Stihl HS56C commercial head trimmer.