DSP radio shutdown
The symptom is that the radio switches off after a short time, but then comes back on. The MID stays lit and functional. This is due to the thermal protection circuitry in the trunk-mounted amplifier.
The amp chassis butts up against the mounting bracket, blocking the air flow from the fan, and causing the amp to overheat and shut down. The fix is to put a 1.5 inch hole in the bracket, opposite the fan opening. The center of the hole is 1.3 in from the outer edge of the bracket, and 4 in from the front edge.
I used a metal-cutting hole saw, but a chassis punch would be a cleaner solution.
The bracket was upgraded in June 97 production to include the hole.
Ed in San Jose '97 540i 6 speed aspensilber over aubergine leather. Build date 3/97. Golden Gate Chapter BMW CCA Nr 62319.