I've got a freeview box connected to AV1 on my TV and an analogue cable box supplying the RF to the TV. When i want to watch a cable channel tho' the RF tuner on the TV i get sound but no picture. The only cure is to switch on the freeview box even though i'm not using it. The problem is related to the RGB/composite switching coming out of the freeview box. Even when switched off there is 2.5V between pins 16 and 17, 0V between pins 16 and 18. I've proven this by setting the freeview's output to composite and the problem disappears. Could i ground the offending voltage by connecting say a 50K resistor accross terminals 16 and 17?