At the risk of stating the obvious, you don't have the rear power button in the always on position, do you? There is a button with a little slot in the ps at the rear of the machine that could be set to be always on, presumably for servers.
Button at the lower left (on a Q650, but this is the same thing ps-wise):
I resurrect this old thread because I tested a bunch of black lcd with know good logic board and good inverter. Basically I simply swapped the black lcds to a known good combination of inverter and logic.
Lcd recapped but the black syndrome stays therefore it must be something else on the lcd circuitry.
Yes a blasting cabinet is great, but hard to see through after a couple of minutes, it's more a hit and miss game.
Yes again, touching the sandblasted metal with your fingers is not a good idea, the damp skin is to be avoided in bare metal.
I will go for a grey or metal finish, but just my point of view.
Concerning the Retrobrite, i have had better results boiling water first, and mixing it with Vanish on a second time (don't use peroxide anymore, Vanish is more easy to use and do more or less the same trick)