Hi @tktk ,
Did you clean the rest of the systemboard as well just in case there was any water under any shields etc?
Turn on the phone and then shine a torch at an angle close to the screen and check if there are any images etc. They will be very faint so trying this in a darkened room may help to see them if they are there.
If there are images to be seen then there is a backlight problem. Since you have replaced the display this puts the problem back onto the systemboard.
With most phones there is a smd (surface mounted device) fuse mounted on the systemboard near to where the display cable connects to the board. The backlight power is fed through this fuse and it may have blown by the water creating paths for the electricity which weren’t in the operating design of the phone, causing excess current to flow through the fuse.
I cannot find the schematic for the phone so I don’t know where it is exactly on your phone. You may be luckier in finding the schematics for the phone which would make it easier to test the backlighting circuit.
If you can’t find any either then perhaps you could use an Ohmmeter and check various likely looking components near to the display cable connector on the systemboard and see if any test open circuit, as most components even capacitors will not test open circuit. Do this with the phone turned off and the battery disconnected from the systemboard
If you find one that is open circuit check if one side of the component connects to one of the display cable connector pins as this would verify that it has something to do with the display. You could also check the other side of the component and see if there is any voltage there when the battery is reconnected and the phone is turned on. If there is then most probably it is the fuse.
@tktk
It has very extensive shielding hasn’t it.
Given that everything else is working OK perhaps it may be safer and would cause less possible problems if you left the shields alone and allowed it to completely dry by leaving it exposed for a day more to the air without any power attached to the board. Perhaps while you are testing for a fuse.
I don't know the phone and I cannot find the schematics or a service manual for it, but if the screen cable connects to the connector near the camera then perhaps some components that I've highlighted in the image below, may be worth testing to see if any of them is a fuse as they look about the right size and shape or any other components around that connector if it is the one that the screen cable connects to.
(click on image to enlarge for better viewing)
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