I just got a Vivitar 2x TC from eBay, and I tried it with both my FA50, a Vivitar PKA 28mm and my DA50-200. It doesn't get aperture data from either lens, it just shows the "F--" as if using an all manual lens.
Is there some setting or something I missed, or should I prepare a return? I cleaned the contacts without any signs of improvement.
(It works ok as a manual TC, especially with the FA50. But well... it would be nice to get what you pay for.)