Hi, I am having a similar problem. Can you pass on the info?
I currently have an EP-15a out for repair at George Meyer AV. I bought mine used from AA and the unit buzzes under heavy load (10amps) and holds voltage steady around 126 volts, not 120 volts. A gentleman named Steve Hogan posted the procedure below on AK, which is why I contacted him initially about doing the repair, but since he never replied I took it to George Meyer. From what I understand, they've worked on these units before and can get the right parts. Hoping to have mine back in a couple of weeks.
"I have repaired dozens of EP15-A units, which have lost the ability to regulate properly and begin to buzz under load. This is almost always due to the voltage regulators on the control PCB falling out of regulation due to capacitor failure. There are several electrolytic capacitors on the control board which were undersized from day one and ALWAYS fail prematurely. I have developed a standardized procedure for replacing these caps on the EP15-A units with higher quality (Panasonic 105C) caps with the correct (higher) values. It is a somewhat time-consuming repair because the motherboard must be removed from the chassis, and the control board must be removed from the motherboard in order to replace the defective parts. I also replace some caps on the meter card, which typically lose value as well. I recently examined a brand-new in the box unit that had never been used, and its regulators were not regulating due to bad caps. If you own an EP15-A it needs to be recapped, and then re-calibrated. Often, the unit's performance slowly deteriorates over time until finally the caps fail so badly that it will no longer work. Recapping with the bigger caps will make the EP15-A work better than new. You may contact me off llne if I can help."
Best of luck!