The solar heating pump for my swimming pool is not powering up as I try to start it for the spring. After some trouble shooting, I've discovered I have power coming in to the controller but now power going out. The solar controller is powering up and showing good voltage at the in terminals. I'm showing no voltage on the out terminals. Both fuses in the controller are good, and I'm showing resistance at the collector terminals. The solar heater has worked fine the previous 3 years, so there is no issue with installation. Any suggestions on further trouble shooting? Thank you.