Here's information on Sony parts ordering:
This webpage might help:
It looks like the HDMI function is on a separate board (HDMI COMPL-F13028800), but I can't be sure without a exploded view. The price listed for this HDMI board is over $100 - but, that was at a Best Buy parts store (who knew Best Buy was into overcharging for parts now?)
So, asking Sony or their parts distributor (lower right on the web page) is probably your best bet, if indeed this is the right part to fix your HDMI issue.
However...Since HDMI sends both audio and video as a single stream of data, I don't believe the HDMI processing could be faulty and still allow audio to work. Instead I have to wonder if it isn't the video processor on the main board causing the problem. Have you tried bypassing all video processing (if the Sony has the ability to bypass, it would be a menu function)? Does audio on the TV still work? If not, it could be the HDMI output function (while HDMI inputs is working).
You may end up getting the wrong part if you are not sure of where the failure is located.Edited by alk3997 - 9/24/13 at 12:05pm