I've seen similiar cases, and symptoms seem to be the same. I'm sorry but most probably the controller is bad.
As if it were other components, the screen would display some sort of error. Also even if you could source the part cheaper, it's not plug n play and Jungheinrich would need to configure it.
On older machine they used three separate controllers, and one was cheaper. This is a combination controlöer thus making it more expensive.