I put two Zenith 520 hd's in a customer's house about four months ago. They worked fine. I went back to do some other things recently and noticed some blocking on the HD channels. I took a look at the signal strengths of sat B and C and they were in the mid sixties to seventies (on all xponders), these go through diplexers because of the age of the house and the inability to wire additional feeds for the HD antenna, so I removed the diplexers and the HD antenna feed from the multiplexer, and I get the same signal strength. My sat finder has the signal strength (at the dish, at the multipler, and the tv location) of B and C in the 80's and 90's (all applicable xponders)as do any other standard sat boxes with the ability to read these signals (hughes GAEBO's and a Sony Tivo). However the signal is low when the zenith box reads it. I might think it was the box, but both HD boxes (both 520's) exhibit the exact same behavior. I tried all the resetting etc. at each change in configuration.

Does anybody have any insight on this one?