I have bought 2 second hand Grundig GDS310 Sky boxes.One is model 2.32 works fine - signal strength 50%, Quality 70%, no problem. The other model 2.64 connected to the same LNB/dish - signal strength 50%, signal quality is only 25% - very low & picture keeps breaking up. This is without altering the dish as it gives such a good quality and picture on the other box. Do you think the tuner is at fault? Is there anything I can do yo correct this fault?