I had the same fault which turned out to be Power Unit Capacitor C315 1000mFd 25volt, rated at 85 degrees centigrade. Its mounted near the heat sink. Look for a slightly domed top of capacitor C315 aluminium case. It should be absolutely flat.
Usual safety rules should be followed. In addition disconnect from the mains while working on the power panel. Give the large electrolytic capacitors time to discharge.
Victor Thompson, March 2008