Wurlitzer 1250

Hello, having used this forum i have always had good responses so here goes again!
My 1250 is not selecting from numbers 30-48. When i press the button there is a loud clunck so it is obviously getting a connection. Having read through the manual i can't see a solution.
Does anybody know if its an easy problem to solve. I don't want to mess with the machine to much as it works fine apart from that. It has been in storage for a while.
Thanks in advance