How to trouble shoot a missing channel - AVS Forum | Home Theater Discussions And Reviews
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post #1 of 9 Old 04-14-2020, 07:51 PM - Thread Starter
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How to trouble shoot a missing channel

Hey guys,

I have a 2000 BMW 5 series. I bought it new and when it was about 2 weeks old, I had the stereo system upgraded with MB Quart component speakers in the front doors, MB Quart coaxials in the rear deck, an Alpine MRV-F400 4 channel amplifier, along with an Alpine M100 mono amp powering an MTX BGE12 subwoofer. There is also an AudioControl EQL equalizer which tuned the frequencies nicely. I had this professionally installed by an MECP certified installer.

Recently, as in the last couple of months, I've noticed that the passenger front door speakers seem to be playing at a really low volume and I can only hear them when the fader and the balance controls are set for the front right only. I'm guessing that the amplifier channel may be malfunctioning and was wondering if anyone knows how to test it. My son has a multimeter but I've never used it and don't know what settings to use or if this would even be the appropriate tool for diagnosis. If anyone has any thoughts I'd appreciate hearing them. Thanks
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post #2 of 9 Old 04-16-2020, 12:17 PM
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This setup sounds similar to what I had in my old 2003 530i minus the eq stage. Is the problem intermittent or constant? If it is intermittent to me that would signal a loose connection somewhere. To troubleshoot I'd first check that all of the wiring is still solidly connected. Over 20 years something may have come loose. I am presuming that the install is pulling the line level outputs from the oem radio in the back and then dumping the powered audio back into the same oem harness to utilize the oem speaker wiring to the speakers. I think I have the schematics still that I used and can try and dig them up if you need them.



Following from that then check all of the settings on the amps and the eq making sure something hasn't gotten switched or adjusted causing the issue. Assuming the eq is not acting as the crossover for the mids/highs can you remove that from the chain to see if that is the problem? Also try swapping channels on the amps between the speakers - this should give you an indication as to if the issue is in the speaker itself or the amp side of the chain.
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post #3 of 9 Old 04-16-2020, 12:35 PM - Thread Starter
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Quote:
Originally Posted by Scotes View Post
Also try swapping channels on the amps between the speakers - this should give you an indication as to if the issue is in the speaker itself or the amp side of the chain.

The issue seems to be constant. The system has such a great sound stage that sometimes it's difficult to tell if there are sounds missing from specific speakers or if that is part of the music. I get great sound from the rear coaxials that blend smoothly with the fronts and it fills in nicely so it took me awhile to notice that something was wrong. Your suggestion above seems to be the simplest and this is what I'm going to do. I have no idea how the installer hooked all this gear up though, so your other comments are a bit above my head. I will definitely check the EQ and the amp settings to see if anything that been accidentally bumped or something but that's unlikely.



Thanks for the reply and your suggestions.

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post #4 of 9 Old 04-16-2020, 12:42 PM
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If you pull pack the panel on the left side of the trunk and post some pictures of the wiring there I might be able to give you a better idea of how they tapped in. That is where the cd changer and radio module would live. I did my install with Alpine amps and a/d/s speakers so am pretty familiar with how it all works and if you are technically inclined it isn't that difficult to figure out with the right schematics.
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post #5 of 9 Old 04-16-2020, 01:42 PM - Thread Starter
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Here is a pic of the area. The two MB Quart crossovers mounted on a carpeted board take up most of the space, and the CD changer has long ago been removed. I have a Dice iPod adapter connected to the CD changer audio cable which is located under the drivers side seat. The iPod cable is run thru the rear center heat vent up into the center arm rest storage compartment where I keep the iPod when I'm in the car.
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post #6 of 9 Old 04-16-2020, 02:12 PM
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Uhhh... is that electrical tape on the speaker wire outputs of the crossovers patched into the oem harness?? When I did mine I pulled the oem Tyco made connector and basically remade the harness as opposed to splicing into it which is what they seemed to have done here. I am assuming those crossovers are for the front speakers and for the rears the coax speakers have their crossover built in and you are not using the rear door highs. Another thing to try is with the audio on just shake that wiring harness a bit and see if anything changes. Good chance if those splice ins are just twists with electrical tape wrapped around them one of them might have gone bad.
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post #7 of 9 Old 04-16-2020, 02:30 PM - Thread Starter
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Quote:
Originally Posted by Scotes View Post
Uhhh... is that electrical tape on the speaker wire outputs of the crossovers patched into the oem harness?? When I did mine I pulled the oem Tyco made connector and basically remade the harness as opposed to splicing into it which is what they seemed to have done here. I am assuming those crossovers are for the front speakers and for the rears the coax speakers have their crossover built in and you are not using the rear door highs. Another thing to try is with the audio on just shake that wiring harness a bit and see if anything changes. Good chance if those splice ins are just twists with electrical tape wrapped around them one of them might have gone bad.

Yes, the crossovers are for the front component speakers and the rear coaxials have their crossovers built in. The suggestion to shake the wiring harness is another good one. I'm putting that on my list of things to try. I really appreciate the suggestions.

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post #8 of 9 Old 05-15-2020, 02:48 PM
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Quote:
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sometimes it's difficult to tell if there are sounds missing from specific speakers or if that is part of the music
I had a 540 of that generation, great car, awful sound system, a BMW hallmark. In a meeting in Munich with their sound team, they wanted stereo sound for every passenger. I simply had to ask "you're the ultimate DRIVER's car, who really cares about the others, since trying to get sound for everyone inevitably by physics will lessen the sound for the driver?" Answer: "Well it's more of a challenge" which was not really an answer. Anyway back to YOUR system:

So FIRST, get your butt out of the drivers seat and maybe into the back leaning over the armrest, so your ears are in the MIDDLE of the car and the reflections are equal from both side. Then forget the music, for diagnostics play something like pink noise from YouTube. Move the fader forward, then left <--> right back and forth.
- This way you can tell if the sound is dead on the entire channel, or just in one driver.
If just the tweeter or just the woofer sounds dead compared to the other side, either the driver is bad or the wiring out of the crossover is bad.
Another simplest thing is to go swap the left and right RCA inputs on the amp, since it's right there, to see if suddenly the other side sounds dead, that would imply a problem in the amp or in the radio or cables feeding it. You can further switch front and back to see what happens.
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post #9 of 9 Old 05-15-2020, 09:11 PM - Thread Starter
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So FIRST, get your butt out of the drivers seat and maybe into the back leaning over the armrest, so your ears are in the MIDDLE of the car and the reflections are equal from both side. Then forget the music, for diagnostics play something like pink noise from YouTube. Move the fader forward, then left <--> right back and forth.
- This way you can tell if the sound is dead on the entire channel, or just in one driver.
If just the tweeter or just the woofer sounds dead compared to the other side, either the driver is bad or the wiring out of the crossover is bad.
Another simplest thing is to go swap the left and right RCA inputs on the amp, since it's right there, to see if suddenly the other side sounds dead, that would imply a problem in the amp or in the radio or cables feeding it. You can further switch front and back to see what happens.
This is an excellent idea. I have a CD somewhere around here called "My Disc: Auto sound 2000 Test Disc" from Sheffield Labs that contains pink noise, tones from every octave, sine waves, channel level tones, etc. I'll copy that onto my iPod and play it in the car. That should allow me to diagnose this pretty easy. Thanks!

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Last edited by Five28; 05-15-2020 at 09:14 PM.
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