I was having trouble getting the E4 code almost all the time. I was fooling around in the back of the unit and noticed that when I wiggled the main connector the unit would reset. After reading several comments on this website about soldering the circuit board due to loose connections I decided to look deeper. I disassembled the unit and removed the circuit boards. Using a magnifing glass I was able to see that the solder joints on the back of the main connector were loose and would move when I applied pressure to the connector. Went to Radio Shack and purchased a 25W soldering iron, solder, and desoldering braid. Fixed it myself and the unit works fine. Small investment for a major fix. Thanks to you all who placed the information on the web.