Maybe the constant power surges to the box have caused it to blow, switching it on and off all the time. But as you say, could also be the box but if you're not moving it or touching it in any way when the psu blows, I'd probably rule that out.
My box is on 24/7 and don't have any problem.
Sorry its not the answer you were hoping for but there's not much we can do without actually getting our hands on the receiver. You could resolder the ground connections on the main board as well as the power supply connection.