I recently misplaced the the 3.5 mm (4-connection) - to - three RCA (yellow/red/white) cable for my Roku Express 3910. I have several similar cables from a camcorder and a flat screen TV. Neither work properly. If the 3.5 connector is pushed firmly into the Roku, the picture is scrambled. If I back it out a bit, the picture is ok but I only get one channel of stereo sound. Is the Express+ designed to work properly only with the AV cable supplied by Roku? If not, why am I having a problem?