Lowrence Hook 2-5 blank screen on sonar

All other functions work, but the sonar screen only shows ground speed and a blank white background with depth markings but no real time depth.  Any ideas? Is there a way to check the connections as far as corrosion other than appearance?

This might NOT be your problem, but I owned a Lowrance Elite-4 that did the same thing you're describing for your HOOK2 and after hours on the phone with technical support I had to send it to Lowrance for warranty repairs (my problem was caused by a circuit board failure).  If you haven't yet tried calling Lowrance, you should.  Their technical support has always been very good whenever I've had to contact them.

Alternately, if you search the WWW for copper corrosion removal you should find some online discussions about products specifically made for removing and eliminating copper corrosion used by those folks who overclock their computer motherboards for gaming.  Those are the only products I know of that can get down into the sockets and pins of power and data cables and make them shiny again.

I'll give Lowrance a call.  I hope I know enough about the FF to speak even remotely intelligently about it.  Haven't been able to really use it since the sonar isn't working.

The techs with whom I've talked are smart enough to be able to speak in plain English - and I was mighty grateful for that.  They're going to ask you if you've updated your unit with the latest version of the software, so you might want to see if there's an update and try to install that before you call.  Saves time.

Good luck!  Let us know what happens, please.

Mine did the exact same thing I rewired it and worked some how and never had a problem again so far.