Black screen after boot

Hi @toms53

The phone needs to be opened and inspected as to what damage has been caused by it getting wet in the past.

Although it happened a long time ago, the water would have caused corrosion to start to occur. The corrosion is ongoing and doesn’t stop until it has been properly cleaned away.

Was the battery removed soon after it first got wet?

Having power connected to a water damaged phone doesn’t help as initially the impurities in the water would have provided unwanted paths for the electricity that weren’t if the phone’s operating design and this could also have damaged some components. Even though the phone may have been turned off there is still power available at various points on the systemboard. The power button is not a power isolating button. It merely signals the CPU as to what is required.

You need to dis-assemble the phone and clean all the affected parts using Isopropyl Alcohol 99%+ (available from electronics parts stores) to remove all traces of corrosion. Do not use "rubbing alcohol" as in some cases this is usually <70% IPA, can contain additives and is not as effective. If you do have to use it, check the label to verify the amount of IPA. The higher the concentration (%) the better.

Here is a link that describes the process. Electronics Water Damage

As always with electronics, especially surface mounted pcb be gentle when handling and especially when brushing away the corrosion. You do not want to remove any components from the board. Clean any plugs and connectors etc as there may be corrosion there. Also remove any shields that may be covering some components and check as well

Hopefully after you have done all this the phone might possibly work correctly again.

Here is a link to the ifixit Sony Xperia Z5 Compact guide(s) that may help