It is absolutely fatal to turn on any piece of electronic equipment if its known to have got wet, as there is always a danger that a normally very low voltage section of the device will receive a much higher than normal one due to the possibility of a damp circuit board shorting out a voltage regulator or a set of parallel circuit board tracks that are carrying voltages of significantly differing levels, or indeed allowing voltage into a part of the circuit that normally doesnt have any. Its not always practicable for a non technical person to remove a part of the case to enable mildly warm air to get blown internally, although this could be tried via the open cassette holder but this is not near so efficient, so its always best to leave any device in a warm environment for at the very least 24 hours before making any attempt to power whatever up. Rule of thumb is, if any device gets wet always remove its battery immediately as the first measure, as although the device might not be switched on part of the internal circuit is always powered.