Thanks for the help, but I do know how to check diodes and what to check them with. There is no question in that the building engineer is at fault and this customer is quite aware of what happens to these units when power is lost, lighting strikes, power surges,vandalism,etc. It is never cheap when they are paying. I only asked about the diodes thinking someone would know which is likely the suspect. I know there is only a few along the bottom of the board to check so I'll be back at it tomorrow.