Help: Cary 805AE Problem?

Hi,

One of my amp completely shut down while I was enjoying the music. All the tubes were bright and then they all suddenly went dark as if it had a black out while the other was working fine. First, I thought it was a 845 tube failure or fuses because I just changed a new pair of Shunguang 845M few hours ago. So, I swapped all the tubes and fuses from the working amp to the dead amp but it didn't change anything. I also put the 845B back that I've used for 3 months without any problem, but nothing help.

I think the main fuse probably blown out but I couldn’t locate where it is. I just saw only two fuses on the back that are tube fuses.

Does anybody know what's the problem?
How can I find the main fuse to check if it was blown out?

Thanks for your help!
Tran