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Car audio problems: MP3 player into CD changer socket

wc123

Jan 31, 2014
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I am new to this forum so please bear up with me. I am also not good with electronics so I hope someone can shed some light on my problem and hopefully suggests a fix.

I drive an old car that doesn't have USB input for the audio, and I don't want to change the car's audio unit with a more modern one because I like the looks of it (it fits the rest of the interior like no after market unit does). But playing music MP3s from a USB is much more convenient than keep changing CDs so I purchased from eBay a USB adapter that hooks to the audio unit and is supposed to play MP3s like it was a CD changer (my car is missing the CD changer). Sometimes it works, but most times it does't.

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Here is what happens:

1) Most of the time the USB adapter doesn't turn on. I turn on the audio unit and the AM/FM radio works but when I switch to the CD mode it says No Disc. When I check the USB adapter I see that the power light is off. If I disconnect the power cable and reconnect it then it works.

If there is a CD in the CD player then the audio unit reads the CD player but doesn't recognize the USB adapter. (Most of the times there is no CD in the CD player though.)

2) The USB adapter is turned on and the audio unit recognizes it and plays the MP3s but it gets stuck on MP3s that are long (such as classical music that is 50 min long). Sometimes it skips the large MP3 files and sometimes it completely stops reading any other MP3 file.

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Here is how the USB adapter looks like (but the one I purchased doesn't have the bluetooth option): http://www.ebay.ca/itm/BMW-Car-Audi...udio_Video&hash=item19e6bb819d&vxp=mtr&_uhb=1

Another thing you need to know about my car is that even when the car is off and the key is not in the ignition there is power toin the 12V cigarette lighter. So if I leave my phone connected to the cigarette lighter and turn off the car overnight and come in the morning, I will find the phone completely charged (I don't do this though!) I am just letting you know because it might shed some light into how the electrical wiring for my car works. I find it odd that the car still supplies power to the cigarette light when the car is turned off. I wonder if this has anything with the first problem I mentioned above.

Any helpful feedback is much appreciated. I am not an electrical person but I am a mechanical engineer so I am not completely clueless when it comes to electronics. May be someone can guide me into how to fix this problem. :)
 

KrisBlueNZ

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So this adapter plugs into the CD Changer connector on the back of your head unit? This connector is designed for use with a CD changer in the boot/trunk of the car?

And the head has a single CD player built in, which works properly?

I don't think the cigarette lighter has any bearing on the problem. Why did you mention it? Is the adapter powered from the cigarette lighter socket?

My guess is that the adapter is crap. (That's the technical term that we electronics folks use.)

It's not unusual for third party products to fail to work properly - the people that design them do not have all the information about the connector and the way that the CD changer is supposed to work in conjunction with the head. If they don't test their product with all possible head units, in all possible situations, they can produce a product that doesn't always work. Their quality standards may be lacking as well.

I would return the adapter for a refund, if possible.

It might be possible to figure out what the problem is, and come up with a workaround, but it's not likely to be easy, nor practical without having an experienced electronics person working directly on the equipment.
 

wc123

Jan 31, 2014
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It works sometimes...

Thank you for the reply!

Yes, my car originally was wired to have a 6 CD changer in the trunk but I bought it used and the CD changer was removed. However, I am not crazy about the CD changer idea so I don’t plan to replace it. So this MP3 USB adapter plugs to the back of the audio unit/CD player in the place of the CD changer. And yes, the single CD player works great.

I mentioned the cigarette lighter because I find it strange how a phone connected to the cigarette lighter gets charged while the car is shut off…it makes me wonder how the electronics have been wired (modern cars definitely don’t do that!) It makes me wonder if power is still supplied to the MP3 USB adapter when the car is off so the adapter shuts itself down automatically after a while and so when I come back to the car and start it the adapter is already shut off and maybe that’s why it doesn’t work? I don’t know--it’s just a random though. (In other words: May be the adapter doesn’t turn on and off with the car.)

I am pretty sure the adapter is a piece of sh*t (that’s a technical term we engineers use too), but I am wondering if there is an easy fix. I mean, it works sometimes so why the hiccups? What’s making it not not working all the time? I decided to keep it because it was pretty cheap ($85) and the seller refunded 50% of the price when I decided to keep it but complained about it not working properly.
How would I go about diagnosing the adapter? I have no problem with opening it but a guide of how to go about diagnosing the problem will definitely be needed as I have no clue where to look! I know it works, but what’s making it not work all the time? That’s the question!
 

KrisBlueNZ

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Ok, thanks for the explanation.

I don't know what the conventions are for powering cigarette lighters. It may have changed over the years. Back in the day, cigarette lighters were used for... lighting cigarettes, and it made sense to have them powered when the car was not running. But in the last 10~20 years, people have been using them more for other functions like charging cellphones, and leaving them powered when the car is not running is risking discharging the car's battery if the charger is left plugged in. So manufacturers could have changed this.

From my limited experience with car audio, I believe the head unit normally gets two separate power feeds. One is ON all the time, and is used so that the unit can remember its settings, and the other is ON only when the ignition switch is at least at the accessories position, and is used as the main power supply to the head unit. Your car might not have the always-ON one; I don't know.

If there is an always-ON power supply to the head, it's possible (but I think unlikely) that it comes out on the CD changer connector, and again it's possible (but unlikely) that the MP3 player adapter unit uses it. If you turn the ignition OFF for, say, half an hour, then back on, does it remember where it was playing and continue from there? If not, I'd guess it doesn't use any always-ON supply.

As for diagnosing the problem, I think you first need to find out what all the pins on the CD changer connector do. Can you find this out? Try Googling the model number of the head unit and some appropriate keywords. Also, you may need to open up the adapter and measure some voltages later - do you have a multimeter?
 

wc123

Jan 31, 2014
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Thank you very much for helping me out!

Thank you very much for helping me out! I am going to do this tomorrow: I am going to search what the pins do. (Later on I will buy a multimeter when needed.) :)
 

wc123

Jan 31, 2014
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Ok, so my car has the "new generation flat pins" and here is a chart of what they do:

http://www.m5board.com/vbulletin/at...t-harness-bm53_new-20gen-20-bm53-20pinout.jpg

The CD player model no. is CD53 E39/53, part no. 65. 12-6 919 066 (build Jan-2002)

The question is: Why does it work when I disconnect the cable to the USB adapter and reconnect it then stops working after a few drives? Why is disconnecting/reconnecting the cable makes it work?
 

KrisBlueNZ

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I don't know why it stops working after a few trips. I need to find out more about how everything fits together.

So the MP3 player connects to just the "B" connector, right?

Can you take a photo of the back of the plug that shows which pins are used, and what each one connects to?

Can you take some photos of the MP3 player, including all of the cables and connectors that relate to it? If you want, take some photos of the insides of it as well.

How does the MP3 player get its power?

How do you change tracks on the MP3 player? Through its own front panel, or through the head unit? Does the head unit have any buttons that relate directly to the CD changer?

If so, how are these commands conveyed to the CD changer, and how does the head unit know that a CD changer is connected? There are two data lines - pin 9 on connector A is called "I-BUS" and pin 9 on connector C is called "NAV BUS". Are either of these connected to the MP3 player?
 

wc123

Jan 31, 2014
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Hello, I just decided to buy an OEM MP3 CD player to replace my OEM CD player. I searched and searched online about these after-market MP3/USB players from China and everyone was complaining about them not working. Even the more expensive Nav/MP3 players from China have bad reputation. So I decided to save my time and money and just get something OEM.

Thank you for your time. Lesson learned. :)
 

KrisBlueNZ

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Bummer. Yeah, it's a lesson that many have learned.
 
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