From my observations when I repaired the unit, it looks like a combination of thin solder bath and vibration damage due to the length of the leads to the IR sensor. This unit worked until they moved to a new house. When they got there and hooked it up, the remote didn't work anymore. The solder joints were cracked. I saw no heat damage on the board, so I don't think heat is an issue. I touched up several other joints on the board while I was there.