Today I had a case that the bmw device alpine CD73 does not work. I tried it on the bench. Turned on the power but the device did not give any signals. I checked fuse near the emitter Q821 as recommended by MrRepair in post number 2. The fuse was faulty. I bridged the fuse and the device worked. I wrote my experience that may help someone else. Of course Many thanks MrRepair.