Unless you know what you are doing do not open up the power supply. Its very difficult to get inside since there are circuit boards on the top and bottom with the guts of the power supply in the middle. I own two Thor units, a TA1000 pre and TA3000 phono, on my phono stage the nut securing the power cord on the power supply came lose during shipping. I opened up the power supply but could not figure out how to open it up to get at the cord, I called Paul Marks and he stepped me through it. There are a number of screws on the board but only 3 of them release the boards and allow you access inside, the others are securing components to the board, so unless you know exactly which ones to remove I would be very careful. I would check all of the external fuses first, both on the preamp and the power supply first and would also make sure there is a fuse inside the power supply before you try to open it up. Good Luck