Oil pressure and charging

Hi
Does anybody know if the Yamaha F115Y (2000 model) 4 stroke outboard suffer with low oil pressure? It only occurs in the first few minutes of operation. The engine does not appear to sound "rattly " i.e being starved of oil pressure but the alarm sounds and indicates that it has no oil pressure. It does not appear to be charging the battery. Is this normally a rectifier/regulator fault?
Any advice gratefully received. Andy

[boats.net]

Need to have compression, leak down and oil pressure test run it. A faulty regulator can cause it not to charge battery.