DAB works but no sound from FM, Sat nav or music inputs

[Tony Coates]

Hi, hoping someone might have some ideas on this one. I recently bought a C250 AMG Coupe (2013) everything is perfect, only issue was CD multi loader didn't work in the NTG4.7 head unit. Having repaired comand units on a couple of my previous MB's including fitting new Cd/DVD players I thought I would take a look inside my unit. CD/DVD unit had jammed for some reason (no CD in it) which was easy to reset. Checked all connections as good, reassembled, plugged it all back in. Now got got "drive unavailable" message (not displayed before) and now there is no sound at all on the sat nav, FM radio, telephone or music from SD card. Bizarrely, DAB radio works although I think its only coming through front speakers. On checking in engineering menu I get NG against FM 1 & 2 antennas and on code reader its says radio antenna 1 & 2 have short to ground. Now that might explain FM, but not the others. If you dial out on phone there is a sharp "crack" noise from speakers which doesn't sound at all healthy, but apart from that no other sound. So possibly two issues here, but can't figure why removing and replacing the head unit could have caused it/them. I believe FM aerial also receives remote key fob message which all works fine so is it aerial or aerial amp? Also, audio amp is being read via engineering unit and is getting signal on MOST and not showing any errors on my Icarsoft MB3. Have tried resetting via various fuse removals with no difference all fuses are fine. Bit baffled by this so would be grateful for any pointers.
Thanks