You got a decoder that went out in this unit this will need ot be replaced ASAP I would not run it until its replaced. The sound going in and out seems to be a
secondary reason for the loos of video and this could be:
1. A bad capacitor on the power supply or boards
2. a fuse or resister has gone out on one of the circuit leads.
I suggest the following:
1. check the power supply for bad capacitors a sign of a bad capacitor would be
budging or leaking.
2. check this into a repair shop if you do not have the expertise.
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