Having trouble on my ZENITH GOLDSTAR GUIDE PLUS TV manuf. in 1999 in Mexico when I switch between the PIP and FULL SCREEN from the MENU button and original remote. No audio on the Full screen when it is above, but I can hear the sound when I switch back to PIP. I'm not sure what to select in order to hear audio on full screen. (VIDEO 1 or 2, F Video, Comp Video, AUX). Your help would be greatly appreciated in regards to my ZENITH. Thank you!