I have just been through this drama with an older Standard Horizon/Navman windpoint. Found in my case that the masthead unit was fine, but that there was an open circuit in one of the five wires in the cable. Unfortunately, the fault lay within the "block" at the masthead that the actual sensor wand plugs into. After a lot of agonizing, a more talented than I pal volunteered to get it apart and fix it. He succeeded, too! He was able to remove the potting in the block with a combination of grinding and then using a hot air gun to soften the remaining epoxy
. The fault was a corroded solder joint at the back of one of the pins. We discovered a similar fault in a second cable that I was able to locate, so It seems possible that your system is similar.
The simple test is to bring the masthead unit down and plug
it directly into the display head
, and then test for functionality. If you haven't done this, give it a try.