Some more info on the subject: http://www.applefritter.com/node/6301

The adapter may be expecting a power source from some of the pins if you have trouble getting it to work. I haven't cracked open my adapter to see if it uses the diode trick since its glued shut. Said adapter does work on my Apple IIgs despite it not having sense pins or H+V sync output (just composite sync on pin 3).