This is not 100% a brick. I have 2 cech-2501a models with the same problem. Grounding the tristate had no effect.
It is a hardware problem. A short somewhere, a blown fuse, a short in the solder under the CPU? I don't know.
But I do know you can't say it is 100% a brick. I have seen it be a brick with this symptoms. But it is definitely not always.