Hi all,
After years enjoying gas-powered equipment ranging from a vintage wheel horse rider to a simple Lawn Boy, I decided to dip my toes in the battery-powered world and bought a self-propelled 80v Greenworks 21" mower.  It has been very impressive, up until today.  Out of the blue, the self-propel boost started to lose a bit of oomph until it declined to an few intermittent bursts.  Now it barely works at all.  Sometimes when engaging it, nothing happens.  Other times I'll get a weak set of bursts of power for a few seconds and it stops.  I have to say, this is quite disappointing, as the mower has only been used about a dozen times since the Spring.  I have no warranty to fall back on, because this was an off-season craigslist pickup (yeah, I know.  Now I'm paying for it..). 
I am completely new to this kind of technology.  My understanding is that units like this use a second motor to directly drive the rear wheel.  Can anyone help me troubleshoot this?  I'm very handy, but I have no experience with this type of equipment.  Am I looking at a cooked motor?  Is there a clutch or gear that I should be checking?  I checked all wiring to/from the self-propel logic board and all connections seem to be solid.
Thanks in advance!