Speaker problem

Hi guys, i need a little help here
I have a center channel speaker that is probably defective
It is turning off the amp channel.
I was first using a yamaha receiver to play with an amplifier
The amplifier channel was going off when i increased the volume up
I tried changing the speaker cables - did  not work
Tried changing the channel - using the center speaker as a front channel - the amplifier was always turning off regardless the change following the center speaker channel
I am curious as what it may be.
A crossover? A drive unit? How do I check what the problem is since I don't get support where I live