so it's not that then
Hard to draw that conclusion from the pics.
- Sometimes a capacitor may leak, and you'll see some sort of wet/oily/acid electrolyte spilled under the capacitor. If the spill was long ago, the wet electrolyte spill might turn into white matte. This is rather rare to see.
- more common is when the metallic can of the capacitor bulges on top, where the dents in the can were made (to release pressure in the eventuality gases are formed inside a capacitor - if vented, must be replaced), your caps don't look bulged at all
- another common failure is when the electrolyte dries out, and the capacity is drastically reduced. This happens first for capacitors near heat sources (placed on the PCB near a power resistor, or near an Al radiator of another component that runs hot. That's easy to check by removing the capacitor and measuring its capacitance.
- there is another type of failure seen in switching power supplies mostly (SMPS), when a capacitor doesn't leak, doesn't bulge, and the capacitance measure OK, yet it has developed a high ESR (Equivalent Series Resistor). Typical audio amplifiers don't make use of SMPS, but I don't know the model you are trying to fix. For other PC or more recent TV/monitors where the power supply is of SMPS type, a test against high ESR caps is by heating the capacitor at 30-50*C or so (with hot air) then powering the device again and observe if it starts working. At higher temperature, the ESR goes down, and often this is enough to make the device run normally again, but at soon as it cools down, the ESR raises back and the device fails to work.