Got a Beemer, stock in car system dead. - diyAudio
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Old 10th November 2008, 04:44 PM   #1
mikee55 is offline mikee55  United Kingdom
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Default Got a Beemer, stock in car system dead.

Hi, been asked by a mate if you can help? He has a BMW 5281SE Estate '98 plate. Its Headunit doesn't turn on., although it displays time and eats and ejects a CD. However, the thing won't switch the radio on, or play CD. It has a seperate Amplifier which has a long oblong double row connector which looks like it has maybe 40 pins?. As well as that, theres a row of thick pins, (which would be power and speaker connections). Apparently the amplifier is the cause of things not working. He showed me the unit, and I didn't have time to count the connections properly. Can't really tell you much else. I just thought, maybe here, someone might know.

Thanks, mike
If it don't work, I'll fix it in the mix! Or visit
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Old 10th November 2008, 05:23 PM   #2
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The BMW radios have a lock out code. If the radio has been locked and he doesn't know the code. it is possible to call the dealer and they can tell him the code based on the radio serial number and the VIN of the car. If he bought the radio used and doesn't have a code...well. its a door stop.

The amplifier has nothing to do with the radio working or not. the BMW stereos have a multi channel amp with built in EQ and crossovers for the multiple speakers. The Headunit sends a 4 channel BTL signal...basically speaker level, so thats 8 wires right there and remote turn on to the amp. the power connections are completely separate from the radio.

The then output Hf and LF to each of the 4 corners so thats another 16 wires and some amps are 10 channel with separate HF, MF and LF to the front and HF/LF to the rears. so thats 20 wires.

The radio itself has its own internal amplifier and you should be able to "Bench" the radio and get it to work. If it wont turn on. its most likely locked out and you will then need the code.

BTW, some models have a problem of the internal amp in the radio will distort before the amp module ever gets to full power. This was a level matching problem when BMW switched from the Becker built radios to the Pioneers. The Pioneers don't have enough drive level to get the amp to full power. this was the case with my 96 850Ci stereo. I used to know what the drive levels were but have forgotten. something like 6vrms in = full power out.

Swapping out the headunit to a Nakamichi and keeping the stock amp and speakers made a world of difference in my car!
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Old 10th November 2008, 11:46 PM   #3
ppia600 is offline ppia600  United States
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There are two fuses the radio uses. One is for constant 12v, and the other is accessory 12v. If the accessory (turn on) fuse is popped, the radio won't come on. I'm not sure where the fuse panel is in that model though.
Don't worry... you can always turn the gain down!
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Old 13th November 2008, 06:25 PM   #4
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Forum NEWB here.... but not a BMW newb

The radios in the e39 5 series cars do not require a code for the radio as the odd ball shape/design makes them useless in other cars if stolen.

Just in case, press in on the volume control knob and hit the audio button. Did anything change on the display below the CD player? Can you change audio sources? Any sound?....


Next try removing, checking and replacing the fuses for the sound system... 2 in the trunk and one in the glovebox. Check the manual for numbers.

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Old 13th November 2008, 07:12 PM   #5
DaveM is offline DaveM  United States
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This site might be of help.

FYI, that head unit is only a preamp. The trunk amp holds everything else. It can be replaced with a standard amp, but it has the crossovers and eq all done digitally. I have an E39 and don't believe there is a code. If there is, you would likely need to take it to the stealer to have it cleared.

I would start by searching the link I gave and here for more info about the wiring.

Then I would find out if it is the amp or preamp that is dead.

That should keep you busy for a while
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Old 13th November 2008, 10:47 PM   #6
ppia600 is offline ppia600  United States
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In addition to what I said earlier, check the fuses for corrosion where they plug in. I found two in the right side of the trunk of a beemer that were corroded and that was the entire reason his didn't play. He was really happy and I didn't have to rewire his entire system with passive crossovers so he could get an aftermarket deck, lol.
Don't worry... you can always turn the gain down!
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