Main board cleaning
Is it ok to clean a main board with the ultrasonic cleaner, when is necessary and what are the positive and negative sides of doing it.
There is no absolute answer to this. My view is that you should not use an ultrasonic cleaner until and unless its absolutely necessary. There are components that may be damaged by the ultrasonic frequency/water. A lot depends on what components are there on the baoard. Generally putting a pcb through an ultrasonic cleaner at about 60 degree C for about 2-3 minutes should be safe and should clean well enough.
There is a video by Louis Rossmann on the same. Even though its seven years old its still relevant. Video Link
There is a more recent video SDG electronics where he tests some of the components and the effect of an ultrasonic cleaner on them - Video Link
Hope this helps.