Let's take another look at the initial installation. That antenna is an omni (circular reception pattern) so as long as it's not mis-installed (somehow grounded to the mast) or defective, it should perform much better than the interior dipole. It likely has 300 ohm terminals (unless self-baluned with a coaxial type F connector) so there should be a 300 ohm to 75 ohm balun between the antenna & your coax type F connector. Make sure it's a single run of coax from antenna to tuner, with no kinks or tight bends, no splitters or anything in between. Any other coax in the house is then irrelevant. RG-6 coax is very good for this application so don't wory about that one bit. Weatherproof any external connections. On your receiver, connect the coax shield to that right "ground" terminal & the coax center-conductor to that middle "75 ohm" terminal. Ensure that none of the shield's fine wires are shorting to the center conductor (both inside & outside) that would kill the signal completely.
Using a multimeter (resistance scale) with the inside coax disconnected from the receiver you should be able to look into the cable & see that balun up top. It may appear to be 75 ohms (or perhaps considerably less impedance at DC) but there should be some continuity present.
Failing all that, your receiver's 75 ohm tap may not be working? Since you know the 300 ohm tap works with the dipole, try another balun inside & connect it to the 300 ohm inputs. Failing that you may even have a defective antenna? Try connecting it into a TV set tuned to mid-VHF channels 4, 5, 6 etc. to see if any signal at all is coming down the pipe. The FM band falls right in between there so if you have no TV signals then that probably explains the lack of any FM.
Using a multimeter (resistance scale) with the inside coax disconnected from the receiver you should be able to look into the cable & see that balun up top. It may appear to be 75 ohms (or perhaps considerably less impedance at DC) but there should be some continuity present.
Failing all that, your receiver's 75 ohm tap may not be working? Since you know the 300 ohm tap works with the dipole, try another balun inside & connect it to the 300 ohm inputs. Failing that you may even have a defective antenna? Try connecting it into a TV set tuned to mid-VHF channels 4, 5, 6 etc. to see if any signal at all is coming down the pipe. The FM band falls right in between there so if you have no TV signals then that probably explains the lack of any FM.