Phoenix Gold MS-275 distorted output

Hi I'm new here, I'm from Italy 🙂, sorry for my bad english.

I have a PG MS-275, unfortunately it have distorted output sound from the two channel.
Two of the four red led are lightly on and the other two are working fine.
I change the caps and check all the transistor but I can't find any problem, also my external power supply is good.
I try also with another pair of woofer but the problem is still there.

The distorted sound occurs more when the music have bass so I think it's something relate with power but I don't know what it can be.

You have any advice?

Thank you!😀