Hoping someone out there with more satellite system than I has some ideas for troubleshooting the following problem.

System: DirecTV with two receivers (Sony/Phillps) each attached to a separate LNB. I am also running DirecPC off the same dish. I should mention that I have some pretty long cable runs to all three systems. The Sony is over 100' but has an inline booster doohickey in the cable (not separately powered). All three systems (sony, phillips, internet) have pretty good signal high 70's to high 80's.

Problem: Usually the Phillips receiver is not in use and is turned off, but when someone watches tv on that system for a while eventually the singal strength on the other reciever (Sony) will drop to zero on most but not all of the channels. Turning the phillips receiver on/off doesn't fix the problem, but I have discovered that tuning the Sony receiver to a channel that has dropped to 0 signal and then turning the Phillips receiver to the exact same channel makes the signal return on the Sony receiver. I haven't exactly diagnosed what activity on the phillips receiver makes the sony one go bad, and I can't make it happen on command. However, it does SEEM like it happens mostly when the phillips receiver is used for a longer stretch of time. Could be changing channels a lot, or maybe just allowing it to heat up, but who knows.

At this point I think something is defective in the system, but I can't imagine what. Looking for educated guesses on whether a receiver (and if so which one), the LNB, or the cabling is the likely culprit and maybe troubleshooting steps to isolate which one.