That was the reason why Apple later introduced their proprietary AAUI port. AUI has the same port as the Apple monitors of that time.

The fuse does not look blown so I first ignored it and did a lot of fiddling with software and a switch to get the external AUI transceiver to work. I learned to things: 1) the switch on this card model has to be set to TK (thick ethernet) to use the AUI port and 2) better check a fuse even if it looks good. 

P.S. actually this card was sold on ebay as a video card - but the thin coax port looked suspicious.