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Just hangin'
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Because the receiver requests either the odd or even set of transponders by sending a 13v or 18v signal to the LNB. A single receiver can only send one type at a time, this it works fine. A DirecTV DVR may need to send both, one for each tuner. Therefore, the need for a dual output LNB. And if you need more than two outputs, you add a 2x4 multiswitch, which will lock the the LNBs to odd or even TPS and then do the switching for the receivers.
 

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Just hangin'
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You indicate that yoiu have a regular receiver and a DirecTV DVR, which means you need three coax lines. The only way this can be done is by having a multiswitch connected to the dish and its outputs connected to the receivers. My guess is that there is a splitter being used to give you the two lines for the DVR. If so, disconnect it, you could damage a tuner in the DVR. You need to see exactly what equipment you have connected.
 

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Just hangin'
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Have you tried swapping the cables on the DVR? Does the problem shift to the other input?
With a low voltage like that there are two possibilities. 1) The Sat 1 input switching voltage regulator has failed or 2) there is a partial short circuit in that cable.

I don't think a phantom power supply will work because the receiver needs to dynamically switch polarities.

A powered multiswitch does lock the LNBs onto the two polarities, but then if the receiver doesn't send the correct voltage to the switch, you end up with the same problem.

Check your connections for corrosion and shorts.
 

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Just hangin'
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30,961 Posts
If you have absolutely determined that the sat 1 input on the receiver isn't sending the correct voltage, it is possible that the voltage regulator on the main board has failed. This isn't a trivial replacement, but can be done if you know where it is located and can get the right replacement part. However, if the DVR is still under warranty, get it replaced.
 
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