Batboard

The remote head (HLN6337D) connected to my 800 mhz trunk mount Spectra has been working fine up until recently. Now when I push the power button on the control head, the xmit and busy lights remain on and sometimes all the the display segments remain on, or sometimes only a few letters are displayed (different all of the time). If I keep the power button pressed down, the radio powers up, goes through the "self check" and then displays the home channel...then there is a constant tone coming through the speaker and the radio appears to be locked. Once I release the power button, only one letter or segment appears in the display and none of the buttons on the head respond (also I can't transmit or recieve). I've checked the connections / cables and they are all good. I've even tried a different head and it works fine. Can anyone suggest any fixes...or is this particular head toast?

Thanks