Hi there and welcome
If the mainboard has failed in these, then having it repaired is not an option as this will exceed the value of the units as the mainboard itself needs to be replaced which is most of the value of the unit.
What I advise is to put the units in a bag of rice and leave for 48 hours
This will draw out the moisture from the units.
Once done, turn it on and if it has not shorted out due to the initial damage, then they will start again.
But in this situation this is your best option.