I was fixing a generic Chinese function generator (Instek GFG-8020H) and after replacing the shorted transistor in the output amplifier, I hooked it up to the scope with an unterminated BNC cable and everything looked reasonable. When I properly terminated the cable with 50 ohms at the scope, the output vanished. I turned the unit off and put an ohmmeter across the output jack. Expecting to see 50 ohms, I was a bit surprised to measure ~400K. The culprit was the protective fuse in the output circuit which measured 400K after I pulled it. It is a standard glass 200 ma fuse (and looks intact). Didn't know that fuses can pop partially open. Guess I learned something today.