Its to do with the common ground (0V DC) the negative (0v dc) side of the IR LED is connected to the Device amp dvd etc , but what happends is there is an inbalance between the 0v , ie one may be just 0.4v higher the 0v causing the problem, my device would not join the 0v together so getting over the problem , already have of these devices installed in real situations and seem to work fine they just need to be put onto a PCB with all the connectors, at the moment they are hard wired..