I had one of those, and yes, there is a fuse. If you plug a mono head set into the unit and if the wiring is for stereo, it'll blow the fuse. Some other guy dove into it and figured out what fuse it is and gave direction how to fix it. I followed the fix and installed a glass fuse holder in there soldered to the points around the fuse. Worked great. I'll try to find the info.
Jesse Bentley (Queasy)
N229Z - RV-8 - Flying - Livin' the dream!