First, I am NOT a technician. Having mostly "export radios", and a Mirage 9900 specifically, I would check for loose solder joints. Export radios are notorious for that issue and I have repaired several by just taking the time to locate the bad connection and re-soldering. If it isn't that, the L.E.D. channel module is probably shot. That is a another fairly common problem, however they usually don't go completely out so I would check all the connections first and hope for the best.