One of my jobs has had very inconsistent building power. I talked to a Schindler engineer and his words were, "Schindler has never built a controller more sensitive to power fluctuations". I have replaced 2 of them with the OEM replacement from Adams. I had a 3rd that seemed to be failing. It actually was the wire crimps that slide into the plug on the wiring harness for the power supply. I changed those and the problem went away.The other 4 that I have, had all the power supplies changed to POWER ONE brand power supplies and I have had no problems with them. I had very little experience working on Schindler equipment until a couple of years ago. The HHT is a good tool once you learn to navigate it. If you now have the tool but no info on how to use it, PM me an email address and I will send you a good, straight forward write up on it.