99C strength should be better than in the 70's. The H20 getting strength in the 70's and HR20 getting nothing may mean that there's significant drop on the HR20 lines.
Before going into the attic, I'd try swapping the receivers.
I know you will only have one line to the HR20 where the H20 was, put at least you can see sig strength on Tuner 1 (or Tuner 2 individually) and rule out HR20 as a problem.
Also, barrel connectors are officially not to be used by Directv. If original installer did that, that's a no-no. I know they work most of the time but every now and then they will cause headaches.
Before going into the attic, I'd try swapping the receivers.
I know you will only have one line to the HR20 where the H20 was, put at least you can see sig strength on Tuner 1 (or Tuner 2 individually) and rule out HR20 as a problem.
Also, barrel connectors are officially not to be used by Directv. If original installer did that, that's a no-no. I know they work most of the time but every now and then they will cause headaches.