The receiver is turned on but no sound comes out thru speakers or headphones (it worked last week). I recall years ago that when I changed a fuse that did fix the problem. I found a package of (old) Radio Shack 4amp fast acting fuses - 250 volt - 3AG or AGC-Type - so this must be what I used. The problem: when I take the cover off the receiver now (unscrew 5 screws) I don't see a place where the fuse would go. (I do see one other fuse but it is shorter.) I downloaded the service manual but I don't understand it. Help is welcome!!
Most modern receivers discourage owner involvement in repairs, even those as simple as replacing a fuse. I can't tell you the location of the fuse, if they are accessible or not. Schematics don't show the physical layout of the receiver, simply the signal flow and circuit breakdown. Fuses are typically located at the rear of the receiver between the entrance of the power cable and the main power transformer. 3AG's would be 3 Amp fuses.
If you can't locate the fuse holder, best advice is to contact Onkyo.