Recently, a local friend from previous repairs brought over a Janome Serger that wasn’t working. The symptoms in this case were that the unit was completely “stuck” in that the manual handwheel could only be turned a few degrees, and the motor would not cause a significant rotation.
Not being at all familiar with these units, nor with sewing machines in general, I pulled open some of the covers and looked inside. Nothing was obviously amiss or out of place, so after removing a side cover, I took the drive belt off (no tools required; just pulls off), and turned the unit on. The motor ran freely and quietly, so there were no apparent motor or electrical problems.
After trying a few things and looking at some online videos of working units, I noticed that the piston that drives what I think is the upper looper was not moving in the malfunctioning unit. Closer inspection showed corrosion between the piston and the sleeve housing it (red arrows in the image)
The quick fix for this was to very gently tap the lower end of the piston assembly (green arrows) downward; I used an old hammer and a screwdriver shaft to do that. That freed the piston, and after wiping some of the dirt and corrosion away and lubricating the piston with just a drop of light oil, and putting the drive belt back on, the serger worked as expected. A pretty quick repair!
I mean, who is this Bob guy anyway, and who would want him as an uncle, the old carbuncle, anyway?