Don't worry about not understanding the math I still don't understand it either. I can't rationalize letters into numbers (algebra and geometry), and I go into Vaporlock. There are enough EE's and ME's and math whizzes that you really don't have to worry about it right now. Eventually getting one of them to sit down with you and learning the in's and out's of Ohms Laws would be another thread with a unit under repair. Resistors will run hot depending on their rating and how close to or over that rating the circuit is actually pushing it. For instance on a FISHER 400-500C-800C there is a 1/2Kohm 7W resistor that runs hot enough to lift fingerprints. And it's running at a little under 4W but rated for 7W. Using a 10W reduces the overall heat as the replacement is larger, but it's still dissipating the same amount. About the only thing the change makes is that you have a slightly larger resistor running the same wattage but is a slight bit cooler. In this case with it being in the POWER SUPPLY and it's fairly crowded in there, a diminished heat source helps the overall power supply resistance to heat.
In the case of the 636, take voltage readings (referenced to chassis ground (black lead to clean,shiny, chassis part) and post all of them here. We'll be able to tell you how much wattage the resistor is dissipating in heat. If it's within spec., the heat is ok. If it's not, then something else is causing the resistor to overload on heat dissipation.
