Did you measure voltage across a piece of coax coming from the LNB connector on the unit, or did you try sticking a probe directly into the F connector?
The reason I ask is...when checking for voltage on the loop-through (aux receiver) connection on my receiver, I made the mistake of sticking one meter probe into the center of the F connector and the other on the shield, but even though the center probe
seemed to be making contact, it really wasn't (thus showing 0 VDC). I almost "let the smoke out" of my receiver as a result.
I'm not familiar with the
Mercury, but double-check in your
installation menus to make sure that LNB power is turned on.
Since you're dealing with
two voltages (i.e., 13 & 18V) for LNB polarity selection, it isn't as simple as finding a power source and piping juice down the coax.
If it's not a software issue, there
may be a current-limiting resistor in the line which could've opened.
Good luck!