Factory Stereo Problems

[93 525 Paul]

I used to have the scratchy volume potentiometer deal but the contact cleaner tip cleared that up. Now the intermittent stereo has turned into no stereo.
The head unit is powered, the stations show, the lights are all lit. But how do I determine whether the head unit is bad or the amp is not powered or dead?
Thanks in advance,
Paul

[BMWDriver]

You'll have to get to the amp, unplug it - and that's gonna be hard 'cause the damn plastic is old and also very tight fitting in there - and take readings coming from the head unit at those wires.

One set of wires comes from the headunit, the other feeds the speakers.

NOT SURE OF THE FOLLOWING : If you get something from the head unit channels, either the head unit is not turning the amp on, or the amp is dead. Why I'm not certain is that I know my modern HU has the option to turn on the amp (would be an aftermarket) or off. As there is a cable for giving the signal to the amp on my Clarion harness, I forget if the e34 has one too. I did not do the adaptor wiring, I had it done. And I can't find the harness diagram I had, which came from bmwe34.net and is now seemingly gone.

Another way is to take out the head unit and take it to a repairman to have it diagnosed. Should be cheap, especially if you're a potential customer. MAKE SURE you have the code of the head unit before taking out, because you'll have fun putting it back in (or no fun at all I should say) if it still works.

My bet's on the head unit, but you never know. I'm guessing that you might hear something faint if the amp is dead.

So, I don't have numbers to measure what at the wires by the way.

[93 525 Paul]

Thanks for the quick response Driver, I do appreciate it.

You'll have to get to the amp, unplug it - and that's gonna be hard 'cause the damn plastic is old and also very tight fitting in there - and take readings coming from the head unit at those wires.

One set of wires comes from the headunit, the other feeds the speakers.

NOT SURE OF THE FOLLOWING : If you get something from the head unit channels, either the head unit is not turning the amp on, or the amp is dead. Why I'm not certain is that I know my modern HU has the option to turn on the amp (would be an aftermarket) or off. As there is a cable for giving the signal to the amp on my Clarion harness, I forget if the e34 has one too. I did not do the adaptor wiring, I had it done. And I can't find the harness diagram I had, which came from bmwe34.net and is now seemingly gone.

Another way is to take out the head unit and take it to a repairman to have it diagnosed. Should be cheap, especially if you're a potential customer. MAKE SURE you have the code of the head unit before taking out, because you'll have fun putting it back in (or no fun at all I should say) if it still works.

My bet's on the head unit, but you never know. I'm guessing that you might hear something faint if the amp is dead.

So, I don't have numbers to measure what at the wires by the way.

I have a Royce manual and I get no fun looking at the '93 wiring for the stereo, but with your suggestion, I now have a place to start. I do have the HU code and it does give faint audio but only on the strongest local AM station, no others. So, more dunno. Hadn't thought about the HU on/off signal to the amp so good point there.
Will let you know whether I learn anything...

[93 525 Paul]

My bet's on the head unit, but you never know. I'm guessing that you might hear something faint if the amp is dead.

Yanked the amp, measured stuff there. The always hot red lead has 12v, the key on hot white/red has 9v. Brown ground leads all have continuity to ground.

So, I don't have numbers to measure what at the wires by the way.

I see on the wiring diagram that yellow/black, yellow/blue, and several others come from the head unit, so I tested them for some sort of signal. I'm no wiz, so help me out here. I set the range on 1v on my trusty old analog guage and got no needle movement whatsoever. I see it has an amperage range, but am not familiar with that. Any suggestions or are we now convinced it's the all allong suspect head unit?

Thanks again

[tim eh?]

Yanked the amp, measured stuff there. The always hot red lead has 12v, the key on hot white/red has 9v. Brown ground leads all have continuity to ground.


I see on the wiring diagram that yellow/black, yellow/blue, and several others come from the head unit, so I tested them for some sort of signal. I'm no wiz, so help me out here. I set the range on 1v on my trusty old analog guage and got no needle movement whatsoever. I see it has an amperage range, but am not familiar with that. Any suggestions or are we now convinced it's the all allong suspect head unit?

Thanks again

if your amp is working properly you should hear a 'thud' from the speakers when you turn the HU on.

attack eagle has some good advice somewhere on bf.com including a pin layout for the factory amp...

i can't really say b/c i never had the stock HU but stock radios generally are garbage in any car in my experience.

[BMWDriver]

Put the volume full blast, and take readings. Vary volume and compare. What's the amperage like ? What range ? Alternatively, if you can ground a speaker on bare metal and touch the other wire on the harness... you should get some sound. The ground is somewhat unknown in the wirings. There's usually 8-10 speakers being driven in the e34.

Since you do seem to get amperage, it may be a working HU. Speakers are rated in ohms capacity after all. And your readings should be dancing around with sound playing, indeed.

I suggest opening the amp and try and determine if anything is unsoldered, burned or damaged. Have a closer look at the wires too.

I wonder that you might also have a busted fuse. I don't think the circuit feeding the HU is the same as what's feeding the amp. Too far back, but I'm guessing here. Look for busted fuses I should say. The fuse boxes are well made, and you'll see a description of what fuses support. It could be as simple as that.

There may be forums revolving around car sound systems, if ever you want to try and find out how to test output and what to look for precisely in terms of amperage and voltage.

And as a final thought, I wonder that an inactive amp waiting to transmit sound should be still outputting something (no sound from HU scenario). I don't remember the wattage of this amp, 100-200W total ?

[93 525 Paul]

Since you do seem to get amperage, it may be a working HU. Speakers are rated in ohms capacity after all. And your readings should be dancing around with sound playing, indeed.

I didn't get any amperage because I didn't try to measure the amperage. I checked for trace voltage bc I am unfamiliar with checking amperage. (And it's easier to check for voltage.)
I did find the following:
How to Measure Current
We measure current 'through' a load. This means the meter will be connected in series with the load, not parallel like voltage is measured. Switch off the multi meter, break the circuit where you'd like to measure current, connect the meter in series appropriately, switch the meter to measure current and turn on. Apply power to the circuit and the meter will display the current going through the circuit.
If the reading is too small, for example 0.001, you can set the meter to mA (label 4 of the diagram). This would give you 1mA, the same for 0.000001 and uA.
If your amperage is calculated to be over 10A, you must use the 10A range. Not doing so will risk damaging the meter.

So I have not "broken the circuit" since I don't see an easy way to do that with the factory plug.
Any ideas?

[93 525 Paul]

i can't really say b/c i never had the stock HU but stock radios generally are garbage in any car in my experience.

I'm not going to argue with that, but it's the wife's car and she just wants some sounds. Happy to replace the HU if that's the prob.

[BMWDriver]

But you do get voltage readings, don't you ? That's a sign that there is current. And this will also dance around like music. I just tried it on my sound system, and it goes dead without sound. I get 0.004V - 0.011V on a small 6 ohm speaker and it varies with music type, and if the music is louder and fainter. If you get a voltage reading with the radio on, full blast, and none with the radio off, then you should have your answer.

Otherwise, the procedure is a bit complicated, but you would basically have to wire ONLY the two negatives from the HU harness to the amp, leaving this very harness unplugged. You would have to plug the speakers harness on.

So, to take amperage, you take your meter and put the red pole on right channel (+) HU and the black meter pole to a right (+) amp channel and check the other HU right channel. Then go to left channels. You must match left and right, but not necessarily front with front because there is only one negative wire per channel supporting both front and rear negative returns. In other words, the amp does not quite "care" if the channel comes in from front or rear because of the way the circuit is setup. But it does matter if left or right. You won't get a reading otherwise.

If you get a first reading, you can stop there and assume the HU is good, and the amp dead. Two to be safe, but you can certainly assume the amp is dead. As to why it's dead...

To make sure it's dead:

Then you can take readings with the HU plugged in and the speakers unplugged, and see what you get, but the tricky part is finding the negatives because now you have no diagram. You now have to dig up the speakers to figure out the wiring colors. I don't think they are the same as the HU, but it's been too long since I've been in there.

Voltage reading is safe if you ground your negative meter wire on the bare metal of the car. If you touch a negative pole on the amp with the positive meter pole, nothing will happen because there are no electrons going from the amp by that pole. And when you touch a positive pole, the vehicle will ground the electrons. And you will be safe too. 0.1V never killed anyone anyway.

Voltage readings ought to be higher out the amp, but if you also want to measure amperage, it's the same as above.

The easiest speakers to get to are the front ones, and I would suggest the mini satellites on the doors. They should have the same color wires as the others in the foot wells, but you never know. The rear ones are hell to take out.

SEE DIAGRAM ON DOCUMENT ATTACHED. I found the procedures I copied from bmwe34.net so I could print and bring to my car. Saved it ! Found it ! It has the HU wiring diagram, but not the amp diagrams. Color schemes did not exactly match my e34.

For 1991-1995:
THERE ARE FOUR (+) AND ONLY TWO (-) SPEAKER WIRES FROM THE HU. With 4 positives to get more power, BMW can half the negatives and save some manufacturing costs, because electrons only travel from positive to negative. If all negative goes on the same wires, it makes no difference because the electrons have already done their job and gone through, so the final exit does not matter; except for right and left that has to be respected to close the circuit. On top of that, it's really a stereo output, not surround 4.0 nor 5.1. But front and rear (+) positives have to be separated to manage fade, but not the negatives.

I'm getting prepared for other electronic projects, so this is no wasted time.

[tim eh?]

I'm not going to argue with that, but it's the wife's car and she just wants some sounds. Happy to replace the HU if that's the prob.

understood.... i wasn't meaning to criticize your standards, more trying to say something like "chances are good it is the HU".

so do you get the speaker thud or not?