Why is center channel dead? - Sony STR-K840P

That particular channel is blown. These are not the easiest units to repair. Given that this is a commercial amp, I would recommend that this unit be brought to an authorized Crown service center for repair. Expect parts cost in the $50 range plus the labor charge.
Dan

The TV can do many things
name 1 thing you can't do
is this a cable box, input dead
or HD TV antenna dead.
or dead wifi to web
or dead ethernet to web
dead net flix,
tell what you want to watch, that would be a nice start

The problem sounds like a dead short issue and the amp is in protection. Check cabling to make sure there are no crossed wires. You can also check by swapping channel 1 and 2 inputs and outs to see if the amplifier passes signal on the bad channel.Also could be an amplifier channel failure if it does not. Have serviced by an autorized service center.

The STR directs sound to the center as instructed by its speaker setup. You say the center does not work on calibration. Is it defined?

Prove another speaker does or does not work on the center output. Then we'll know if it's the receiver or the speaker ensemble that has the problem.

Have you checked the manual for this "
There is no sound, or only a very low-level sound is heard from the center/ surround. "?

repeat your setting and check you control button and sliders--------try to exchange the cables if the good channel become dead change the cable.
if you did all above and still not working ask for help from service center.

Check your audio settings, via the on-screen menu. The center channel may be turned down. When set at -5 to -8, the center channel speaker may be practically inaudible. If raising the volume of the center channel does not solve the problem, then you do have a dead center channel. The system would then be in need of repair.

Be sure the sound source has a center channel output ie. not a 2 channel source only, try the test tone setup for 5 or 6 channel balance, if no sound from the center channel still then it is looking like maybe the center channel is blown.

I had a similar problem with a jvc 8040. when I replaced the fuse it became very obvious that the b1560 output on the center channel was blown (smoke and sparks, always a dead giveaway). I haven't fixed the center channel yet but simply unplugged the center channel board and removed it from the unit. Now everything works fine except of course the center channel. Pre outs still operate just fine so a slave amp could be used for center channel power, or you could just go and buy a marantz amp; I did and then I realized that I was lucky that the old jvc quit.