I have yet to see a Scientific Atlanta set top box that has discrete power commands, but that shouldn't stop you from trying. These days I think the JP1 group is finding new discrete commands better than people with Pronto's.
If it uses the Scientific Atlanta protocol, then there are only 6-bits that vary (64 total possibilities). So if you use the "test all codes" method you will probably send each command four times or you could be scientific and create a device upgrade and try OBC's 0 through 63. But learn a command first to get the device and protocol .
I once measured the current consumed by my set top box and it was the same on or off. And 110 mA at that (~$4/year where I live, if I did the math right). So the simple solution is to leave it on and not worry about it. In fact you might key move the power command to something obscure and key move a bogus command, so no one turns it off. I have said, more than a few times, that the little power led's were a giant practical joke on the part of STB designers
