I found this au-7900 at a garage sale awhile back and decided to Crack it open and take a look at it and from what I can see it appears to be 100% original in other words nobody has ever done any work on it before..First thing was put it on the dbt and the 80w bulb glowed bright so my first thought was short circuit some where so took it apart and pulled the power amp board f-2596 out and checked all of the op transistors and they all test good..did some dust cleaning and making a parts list now..