extruder front cooling fan replacement
An i3 MK2S Repair Report (in case this is of use to others) :-
We noticed reduced print quality (more melted filament oozing?) and took a closer look. It seems that a print failed weeks ago, leaving a "filament cloud" and melted filament on the extruder, somehow some of the filament became lodged in the extruder's front cooling fan. Then four fan blades had broken off on one side of the fan, and two on the other side. I ordered a replacement fan from PRUSA. After removing the circular PRUSA fan adhesive label, I desoldered the old fan at the point the wires were soldered onto the fan PCB (to preserve as much wire as possible). Then not wishing to disassemble the extruder, rewire the extruder cable bundle, etc., I instead I soldered on a female 2-pin JST connector to these red-black wires. Noting the polarity, I then soldered a red-black wire-pair with a male JST connector to a new fan, connected that to the female JST connector, tidied the wires, and everything works. In retrospect I should have shortened the original red-black wires a bit for neater cabling.
One possible benefit of this JST connector approach is it will allow easy replacement of the replacement fan if it too fails in the future.