I've done Catv and Sat. Doesn't matter what you work on Digital Signal is Digital Signal. Before I just started changing out parts, provided what is say is correct, that the birds are tuned in correctly, the dish is plumb etc. Start checking for bad connectors at your reciever, ground block, dish and any splices that may be in the line. You said the LNB was damaged, from what? If it's a power surge it might have gotten a connector. HD doesn't like cheap screw on or crimp on connectors. That is where I'd start anyway.
Life is what happens while you're busy making other plans
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