Originally Posted by JeffVanter
Does anyone know how I can fix this?
Suggestion #1, take it to a tech.
If You're capable and comfortable in opening a wall voltage device, and are knowledgeable about things like draining the PS caps, open the amp up and diagnose the problem little deeper.
Sounds like the circuitry that defeats the speaker when the headphones are used is working all the time.
Assuming of course that the headphone out still works.