I just got an RPi 2. I'm using NOOBS. I want to connect the RPi to a small screen I bought that takes NTSC composite input. For now, I'm testing on my TV, which has HDMI and composite inputs. I tried modifying /boot/config.txt to include sdtv_mode=0 and sdtv_aspect=1 and rebooting, but I still only got a signal over HDMI. I checked that the cable I'm using matches the diagram at this diagram using a multimeter. The sleeve of the TRRS connector connects to the connector pin of the red RCA connector and ring 2 of the TRRS connects to the outer ring of all three RCA connectors. If I run sudo tvservice -c "NTSC 4:3" (per this question), the HDMI stops working (which I expected), but the result was a dark screen on the composite video. It's not no signal. Everything is just black. I guessed that terminal is still open, and if I run sudo reboot now (though I can't see what I'm typing), I momentarily see the raspberry logo over the composite video connection, then a blinking cursor, then the RPi reboots in HDMI mode.
How can I get this to work in NTSC? Thanks!