Can I repair my hedge trimmers?

Hi, I have two, the larger is a Black & Decker GT670. The motor spins up okay and the drive turns as well, and I can make the blade parts move by turning the cog whilst it's not attached to the handle. If I assemble it though, the motor runs and I can hear that the drive is going but the blades don't move. I've taken the blade assembly apart and it all looks good, the spring-loaded cogs look undamaged and complete, it just doesn't move with the motor attached.

The other is a small Bosch P80K which was working fine until yesterday and then suddenly started running slowly, all working - just slow. Stripped it and cleaned it, removed some threadlike material that was in the drive cogs (thought I'd sussed it then) put it back together but it's the same as before, all moves - but slowly. I'm wondering in this case whether one of the contact brushes is worn but I'd have thought that would just bring it to a stop.

Any ideas on either of them?