I have a late Model M keyboard - p/no 1391406 with 'hard-wired' cable. When connected, none of the keys respond and all the LEDs flash constantly. I tried replacing the capacitor but this hasn't helped. there's not a lot else on the board so guess it could be the large IC (see photos) which, not surprisingly, doesn't seem to be available anywhere. Is there a replacement board/circuit available? (possibly USB?)