Braun Multipractic Model MR72 -- When pushing the green button to activate functions, nothing happens. Green button engages with small black switch in the top of the unit which contains circuit board. Do we need a new circuit board or switch? Or a new Braun stick blender?

Better to examin from a technician, i guess you have to buy a new one.

This can be a problem with the switch or with the circuit board for the mean time I will advice you first to change the switch if that still didn't fix the problem circuit biard is the problem........

It need to be tested, testing the switch is easy you just need a multimeter, regarding the motherboard, that is more complicate, but if you do not find any other cause, then you replace the motherboard.

Ok..and the power is known good condition?