How to get both uhf AND vhf channels?

I have a channel master 7777 preamp. From my atenna to the preamp, I just have a single coax cable. Here's my issue:
The CM 7777 has two places to connect the coax from antenna. One is "VHF". The other is "UHF and/or Combined".
When I connect the coax to the VHF I get good reception for channels 2-13 as I should (but no other channels). So, I assumed that I should hook the coax up to the UHF and combined. That DOES get me reception for channels above 13, however, I no longer get the channels 2-13. I figured that since it said "combined" , it would get me reception for both uhf and vhf channels. So, I'm obviously doing something wrong. Do I need to put something between the antenna and the preamp other than just a line of coax? (perhaps a splitter of some sort?) How do I get all channels, rather than one set or the other? Thanks!
It has to be an older CM 7777 to have separate inputs. The new one has a single input. There is a separate combine switch on the older one that needs to be set in the correct position when you change the inputs. If you've set the switch correctly, and it still doesn't work something else is wrong. Failed switch?
The switch is on the back side of the circuit board from where the inputs are located.
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