#K40OpticalEndStop
I recently repaired an optical end stop for a community member and felt it was time to share the repair procedure.
Since you cannot buy replacements (at least I have not found them) I figured you could try and repair your own end stops.
Its pretty straightforward if you have basic soldering tools and skills.
Take a read and let me know if there is any thing I missed or is unclear.
My k40 end stops are hall sensors. Not optical so be aware of the many options
@Paul_de_Groot mmm it does say 'Optical" :)?
Nice guide! Dont have the optical ones myself, but i see the problems with them almost every day. Good to have a guide to link! 
@HP_Persson I have used optical sensors in this kind of applications for years so I was surprised there were so many problems, especially touted as electrical noise. Now I think its because there is a design problem with these (incorrect pullup) and the sensor gets clobbered by the interposer.