If the dispenser isnt opening then what you need to do is remove the outer door panel.
From there you will see the back of the dispenser. It will have two wires going to the coil on the dispenser. With a multimeter you need to test the coil and if its faulty then it will need to be replaced from there.
But if the dispenser is fine then the control unit will be the problem.
But most of the time when you get this fault its usually a faulty dispenser unit.
Yes thats fine or if you use tablets just place it in the cutlery basket as it will work fine like that.
I know people who never use the dispenser they just throw it into the cutlery basket and it will work perfect from there.