Speed controller quit working

[Dgard65604]

My son got a new HO set for Christmas. The speed control worked perfectly at first but now it won't change speeds. It runs at the fastest speed at all times. Any thoughts or do I have a defective controller? I'd it's defective that's disappointing after one days use.

[ACY]

It sounds like you broke the knob by turning it too hard or too far.

[jbrock27]

Is this a Bachmann controller?