Hello, I just registered to post the issue I just had with an older KX 600.4. It would either flash protect or come on but have a horrible signal with lots of interference. When I opened it up I saw some type if brown glue like material on some of the components.
I remembered seeing an EEV Blog video a while ago about some bad bookshelf speakers with the same brown goop. Testing the glue for conductivity revealed it was conductive enough to transfer voltage. The glue was originally a non-conductive glue (that was never needed in my opinion) but over time become more and more conductive.
After removing all the brown goop both Dave's bookshelves (EEV blog) and my Kicker KX worked perfect. I failed at taking pics but if this is problem its easy to diagnose by checking resistance of the glue with a DMM. If it doesn't read zero or "OL" carefully remove it all with a plastic pointy bit and hopefully back in business.
Good luck.
