It's been driving me crazy trying to figure out what's wrong with my rig, and I'm freaking out a bit because I have a 4 hour gig tonight. I have an ampeg pf-500 head and 2 115 cabs. Long story short, 2 different heads stopped powering (or at least making noise) my cab, plugging headphones into the amp head worked. Is it possible for a power cable to be faulty in a way that it doesn't provide enough power for the amp to power the cab, but still kinda work? Ok now long story long. 2 weeks ago in the middle of practice my rig cut out, amp still had power and the fault light was not on. I swapped out everything frantically in the middle of a song, instrument cable, speaker cable, even a different bass. There was an extra amp head there so I tried that and everything worked. I figured my head had gone bad so I bought a new one (PF-800 this time). I wanted to be sure so I used my old and presumably bad head at home the past 2 weeks trying to reproduce the problem and it's worked fine. Finally last night while trying out my new head it happened again. I was more methodical this time swapping everything out one by one, although the first thing I tried was plugging headphones into my head and that worked! I pulled another cab over and plugged into that, still didn't work. The only thing I hadn't swapped out was the power cable, but that involves restarting the head which also fixed the problem. So I THINK the power cable was the only component I didn't switch out meaning that's most likely the culprit, but I'd like a sanity check before the show tonight.