Other than checking fuses, or something obvious, I would not get into it. In most consumer electronics, yes even expensive audiophile boxes, the main purpose of a fuse is to prevent fire. For instance, if your transformer develops a short, you don’t want it catching fire. Your best bet is to always take it to the manufacturer for service. If modifications or upgrades are needed, they can take care of them. They will be familiar with the unit, have the correct parts available and it should be done right. If that is not possible, take it to a known good audio repair technician that works on this type of equipment. Most consumer electronics nowadays is not mean to be serviced.
Hope it works out for you.