I have a LX-15 Spa Builder control system. My Display/Control panel has six buttons for control of a blower, 2 pumps and a light. The pumps, lights and blower will not operate off the displaly buttons, but the arrows do work. I dont know how to isolate down to which componet to replace. The display controller has a phone jack in.

Help.

It is most likely the topside control that is in need of replacement. They go through an intergrated circuit (chip) that translates it to use the 8 pin rj45 connector to go to the main board. Most likely you have a bad circuit trace in the topside. If it were me, I would replace the topside control first.