The peaking function works and it displays the signal level for all the stronger channels. If I use the channel function and select the broadcast RF channels for the two stations of concern, it just displays the two hyphens (no signal) in the signal box and, of course, no picture on the TV. Even with the gain at 20, the strongest channel here will still show picture on the TV so I don't think the two weak channels would over drive the TV, but I will try all suggestions.
I'm thinking that the SensarPro just doesn't pass on any signal to be amplified as long as it shows no signal in the signal box ie it just doesn't "see" the weak signals.
The fact that the weak signals get to the TV with the old power supply would suggest that connections etc are likely okay but I will check all.