If your cards are o.k. on the KN2600 it does suggest your KN7 is at fault. However, I am not an expert on these matters but I know a man who is and he has been a great help to many on this forum, particularly to me.
May I suggest you ask TechnicsPlayer for help? He's your man!
PS I heard today that spare parts for Technics instruments will become obsolete at the end of next year - makes you think doesn't it?