[NickRay]

Tired of this problem which the car has been plagued with for years now. The drivers side front door speakers will fade in and out, and the rear deck speakers will sometimes crackle or not operate at all. Running over a bump in the road will bring audio back or take it away. Cranking the stereo to max will bring back audio in the drivers door speakers.

Looking for new ideas of what to try.

I have ruled out:

1. Amplifier
2. TCU
3. MULF
4. Radio
5. Dension 500S BT

I have tried multiple radios in the car, and all of them present the same issue. I currently have a (rare) 65129350505 in the car and it resolved nothing. I replaced the amplifier with a JLXD600/6 V2, which also solved nothing. I have tried eliminating the TCU/MULF2HIGH/Dension 500S BT (in every combination) from the MOST loop with MOST terminators, and that once again did not change anything about the speakers crackling etc.

I have removed the driver side front door card and both speakers measure 2ohm, as they should.

It seems like the only thing left to do is remove the radio, short every single audio wire to ground, and measure resistance from the amp side of the harness for each signal to ground, and each should be more or less 0 ohms. Unless anyone else has solved this g****mn problem and has some ideas I should try.

Thanks!

[NickRay]

Also, the car is an 09 328i with 676, 6FL. No iDrive. All factory speakers. Every audio input exhibits the same issues (Lightning from Dension, FM, CDs, etc)

[GSB]

That is frustrating to the extreme. I initially wondered whether the optical fiber in the MOST bus might have been kinked or broken somewhere along its length. It's a fully digital connection, transmitting and receiving pulses of light at very high speeds. A kink or break will still transmit light, but the light strength might be varying as the cable is jiggled while driving, and therefore the amp would be receiving partial or unreliable data. That could certainly explain crackles or complete audio dropouts, but I doubt it could explain why some speakers might be working consistently, while others are not.

Corrosion of the connector pins in a speaker wiring harness can certainly cause intermittent connections, and a wiring harness accidentally pinched or hit somewhere along its length could cause intermittent connections and/or shorting too. I've seen that happen in several electronic products before. Sometimes right out of the factory. It might be worth tracing out your harness with a multimeter. Unfortunately, an intermittent connection is very frustrating to find, because it might be perfect one minute, and not the next. Temperature, movement, impact, and so on, can all have an effect.

[NickRay]

Yeah that was my worry too. I think it’s time that I buy a better multimeter and measure out the harness. It’s funny because I saw another thread about this exact same problem and the last reply is also “time to get the multimeter out”. I feel like this is some endemic issue with E90s these days??

[ctuna]

You might try injecting a hardware signal at the amp inputs that would
at least isolate the problem to the amp and speakers. If you are going over
bumps and it causes it to intermittent harness inspection and shaking it
while it's on might tell you something.
I didn't see you mention which speakers you have.

[GSB]

Originally Posted by ctuna

You might try injecting a hardware signal at the amp inputs that would at least isolate the problem to the amp and speakers. If you are going over bumps and it causes it to intermittent harness inspection and shaking it while it's on might tell you something.

I agree. That would be fantastic. Unfortunately, the amp input is fiber-optic and the communication protocol is BMW-specific. However, an aftermarket amp might provide another analog input. Another idea below...

Originally Posted by NickRay

It seems like the only thing left to do is remove the radio, short every single audio wire to ground, and measure resistance from the amp side of the harness for each signal to ground, and each should be more or less 0 ohms.

NickRay, what you suggested here, shorting each wire to ground and measuring it at the other end, will not help if the harness is pinched and shorting to the body or shorting to other wires in the harness. Furthermore, while driving to reproduce the fault, you will not be able to watch the multimeter closely enough to see short glitches. Plus, the multimeter is too slow to respond to momentary glitches in the harness.

I'd disconnect the amp and inject an audio tone or music into the amp connector, driving one speaker at a time, starting with that problematic driver's door. Then you can drive around and you would instantly notice if it cuts out.

If the injected sound does cut out, you can be sure that there's a bad connection somewhere in the harness, connectors or speaker. And you can confidently rule out the fiber-optic MOST bus, the radio head-unit and the amp.

However, if the injected sound does not cut out, other interesting things could be happening. For example, a pinched harness can cause wires to short together without breaking the wires. You would certainly hear if the wire pair to the driver's door speaker was shorting to itself, but you would not hear any change if one of the front speaker wires was shorting to one of the back speaker wires; whereas a car amp may have short-circuit protection that could shut down channels where such problems are detected.

[NickRay]

ctuna The car has the stock HiFi speakers, no changes there.

GSB good point about shorting them to ground! You are right about that not being helpful in the case that the short already IS a short to ground.

I think the best path forward sounds like what you guys suggested: wire up an analog audio output and drive each channel on its own from the amp side of the harness. That way I can drive around and see if anything cuts in or out, independently. I have an old headphone amp I can hack up to do this, and it can throw a good bit of gain as well. This way I also don't have to care about the amp or radio themselves, and only focus on the wiring and speakers, in individual channels.

This will probably be a task for this weekend. I will update you guys with findings when I get to doing this.

[ctuna]

I have and xd 600/6 myself and it's a lot of power for the stock speakers.
Stock Hi Fi's at 2 ohm will be pulling 100 watts rms per channel rather than
the estimated 12 watts out of the stock hi fi.

[GSB]

Originally Posted by NickRay

ctuna The car has the stock HiFi speakers, no changes there.

GSB good point about shorting them to ground! You are right about that not being helpful in the case that the short already IS a short to ground.

I think the best path forward sounds like what you guys suggested: wire up an analog audio output and drive each channel on its own from the amp side of the harness. That way I can drive around and see if anything cuts in or out, independently. I have an old headphone amp I can hack up to do this, and it can throw a good bit of gain as well. This way I also don't have to care about the amp or radio themselves, and only focus on the wiring and speakers, in individual channels.

This will probably be a task for this weekend. I will update you guys with findings when I get to doing this.

I've just thought of something. Playing audio through the speaker harness will definitely help find a broken wire in a speaker pair, or a short between both of the wires in a speaker pair. But it will not find a single wire that is shorted to the body.

You can find those by using a multimeter with a low-resistance beep function. Test each wire's resistance to the car ground/chassis. If you don't find any shorts, you may have to leave the meter connected to each wire in turn and drive over bumps to find any intermittently beeping shorts.

WARNING: Do not accidentally touch the 12V supply pin while measuring resistance. You can blow up the meter.

[NickRay]

Try, try again, the car says.

I setup an amp to drive the speakers individually with an iPad and drove around playing music in each of the 4 channels (didn't try the subs) and no crackles or otherwise weird behavior, and I drove over bumps on purpose to try to spur the issue.

Next I measured out all the channels between - and +, and saw 4ohms on channels 1 through 4, and ~3ohms on the subs (channels 5 and 6), which I believe is expected since the mids/tweeters are wired in series.

The 4 input channels all measure open between +/-, which is good.

I connected everything back together, and now the issue isn't presenting itself at all. I wonder if this really could be a temperature related issue in one of the digital systems rather than a harness issue, but right now I am at somewhat of a loss. I am going to wait for the problems to show back up, which I'm sure they will eventually, then take more measurements.

Thanks for the ideas to try GSB. My multimeter is not very sophisticated and I still haven't bought a new one, I think there is one at work which I can use soon. Driving around with the meter on beep mode connected to each output channel would work. But if the problem is due to an input channel, I think I would need another approach.

[GSB]

Man, so frustrating! That seems to be the nature of the beast when it comes to intermittent issues. You're doing a great job, though. It really can be a lengthy process of elimination. When it comes to the electronics, the temperature can certainly have an effect, and so can humidity.

[ctuna]

Connections are the enemy of electronics.
I worked repairing semi conductor test equipment and many
times I just pulled the board out put it back in and things
started working. Reseating the connector Power down
is usually what you start with when you want to save time.
You can buy Scope multi meters combo's these day's
for under a 100 bucks . Don't know how good they are
but should be good enough for audio.

https://www.e90post.com/forums/attac...3&d=1329017429


Meter Checks and Power Up
I use my meter to record initial values of speakers and verify that those values
appear in the right places . If anything goes wrong I have a chance of finding it.
Stock door speakers measured 3 ohms at the amp tightening screws
Stock under seats measure 2.1 ohms at the amp tightening screws
Dotechs measure 3 ohms at the amp tightening screws
Jehnerts measure 6.2 to 6.5 ohms at the amp tightening screws

I don't see how you could get 4 ohms from Hi Fi speakers from the harness
in the Trunk to the speakers , unless you are not subtracting the lead resistance.

[NickRay]

Thanks GSB! Yeah, intermittent issues are really hard to figure out.

Agree ctuna, especially anything custom. My DMM is pretty garbage, those were just the measurements it showed. I don't have a Fluke or anything nice.

Promise to keep this thread updated as needed. All day today it was behaving without a single signal integrity issue. So I continue to be confused, yet maybe happy that it is "just working"? Idk. Once I have access to a better DMM I'll re-take the measurements at the XD600/6 screw terminals and compare to your measurements ctuna. Also thanks for posting your install guide, very nice work you did on your setup. Looks professional.

[ctuna]

Hi Fi system is a simple analog system sorta . Analog in and
analog out no Fiber optics involved .

[GSB]

Originally Posted by ctuna

Hi Fi system is a simple analog system sorta . Analog in and analog out no Fiber optics involved .

Ah, gotcha, NickRay has the 328i with the HiFi amp, not the Top HiFi amp with fiber-optic MOST bus input.

Yes, in that case, just drive an audio signal into each analog input and listen for crackles and audio cut-outs. No need for the multimeter with beep function, then!

[NickRay]

Some time has passed now, and issues are still gone. Wish I could troubleshoot this problem to completion, especially because it seems like I’m not the only one who is experiencing this on E90 chassis, but unfortunately/fortunately it’s somehow resolved itself.

[GSB]

That's great, though annoying that the issue might still be lurking. As ctuna mentioned, connectors can definitely be a source of trouble. I've also had electronics problems that only show up in wet/humid weather. Any kind of contamination on a circuit board seems to absorb and retain moisture from the air. So keep that in mind as a potential contributor to the problem too. DIY: How to Save Your Electronics After Water Infiltration or Contamination