Took apart an Apple TV due to no power from the smps and its like 80% covered in a white rubbery adhesive.
I'm used to seeing this stuff (or similar) on bigger components like electrolytic caps to minimize vibration but I'm curious it's purpose on the bottom of the board where it's all smd? Other than to make it really annoying to chip away to test components
Its a type of RTV silicone adhesive that helps prevent component vibration, larger components like capacitors are normally secured by it as any excess movement in them can add to the chances of broken solder joints. I can only imagine its been added here to help secure the transformer etc but has been applied in a really shoddy way
It's white RTV glue/silicone (room temperature vulcanization silicone). It's used to mechanicaly fix though-hole components to the board. The covering of the SMD components on that board is unintentional as they wanted to fixate the transformer and capacitor.
It's partly for mechanical reasons, and partly thermal. RTV silicone is not a great thermal conductor, but it's a lot better than air. It helps conduct the large amount of waste heat in a power supply to the inner walls of the case.
If you replace it do not use acetic acid cured consumer silicone, use an electronic grade encapsulant.
