BMW Repair: BMW 528i, FM radio, antenna amplifier, diversity antenna

Question
Tino,

I have a 1996 BMW 528i. The AM radio works fine but when I switch on the FM radio, I only hear a buzz. What can I do to find out if this is to do with a problem within the radio unit OR if there is a problem with the FM amplifier located in the rear C arm? Pl. also advise which rear C arm (right Or left) contains the FM amplifier unit and how to identify it?

Thanks,

Janak.

Answer
Janak,
The HiFi/TopHifi amplifier is at the left side of the rear compartment(behind the trim cover right after the left rear lights). It is beneath the NAV if your car has NAV.
This amplifier amplifies sound signals of both radio modes
(not just AM but also FM) and cassettes or CD's. So if the AM radio sounds, the amplifier works and the problem is elsewhere.
The problem could be any of the following:
a) The diversity antenna system made up of the ribbon antenna in the rear windshield, trap circuit, filter, the antenna amplifier and cables in between components up to
the radio itself and the amplifier. Oftentimes, the ribbon antenna gets cut when window tint is installed. Also, the antenna cable connection to the antenna amplifier located at the left C pillar and the other trap circuit on the right C pillar gets loose with time. The C pillar is where the rear windshield is attached.
b) The radio unit itself (Business CD/MID/or OnBoard Monitor Radio)

My suggestion is to check first if it has aftermarket tinting, if yes, then there is a big possibility that the antenna connection had been cut and there is virtually nothing that you can do about it. Then check the cable connections to left and right C pillars and also the amplifier. Tighten any connector that is loose and recheck if it corrects the problem.
If not, replace the radio unit.