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Adding Aux input to older car stereo

Discussion in 'Troubleshooting and Repair' started by DoubleDogDan, Jul 20, 2014.

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  1. DoubleDogDan

    DoubleDogDan

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    Jul 20, 2014
    I have a 2003 Mitsubishi with a MR587268 AM/FM CD player. I'd like to add an input for playing things like my phone & MP3 players thru the car's audio system. The player has an input for an optional trunk mounted CD changer, which I do not have. This connection contains leads I am assuming are for left & right channels (labeled "CD-CH Lch" & "CD-CH Rch", in the service manual) as well as "Signal Ground" (see attached). Seems like these would be usable input paths. If so, how would I "tell" the player to use that input, rather than the tuner or build in CD player, when I wanted to use an MP3 player? I do still want to be able to use the stock radio/CD player. Is there a better way to accomplish this goal? I used to get inputs into the amp in a TV, radio, etc. by connecting to the volume control wiper/center lead. Thought I could do that with a jack that's switched to disconnect the lead presently connected to the wiper & connect the MP3 leads when the 3.5mm plug is inserted. Ideas???

    The specs for this player state that a feature it has is "CD-CH, MD-CH control". Not sure what this refers to, I'm wondering if this relates to switching between the "CD Changer" & the tuner/single disk player?

    TIA

    DDD
     

    Attached Files:

    Last edited: Jul 20, 2014
  2. Gryd3

    Gryd3

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    Typically the CD-Changer port requires data as well as the audio channel.
    There are after market kits available to allow USB to CD-Changer ports, as well as generic Audio Inputs.
    If anyone on here knows how to bit bash the CD Changer protocol, you could do it yourself ;)
     
  3. KrisBlueNZ

    KrisBlueNZ Sadly passed away in 2015

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    There was a thread a while back where the guy had bought an after-market unit that pretended to be a CD changer but played MP3s - just what the OP wants. He had bought it through eBay. It never worked properly. So be wary of buying anything that's not made by the manufacturer that made the main car stereo component (the "head"). They are the only ones who really know the data communication protocol used between the head and the changer.

    If you have (or can borrow) a genuine CD changer, and you have experience with serial data protocols, you could reverse-engineer it, as Gryd3 suggests. If you're careful and thorough, you would probably succeed.

    Otherwise you can just hack an external stereo audio input in at the volume control, as you suggested. This would only work if the head is simple stereo (or simple stereo with front/back fader), and if the audio actually goes through the volume control; neither of these are necessarily true for modern heads. You would need to hack the socket somewhere accessible, so you could unplug the MP3 player if you wanted to listen to the radio or the built-in CD - assuming you want that option.

    It looks like Digi-Key have four suitable options in 3.5 mm stereo dual-switched jack sockets:

    http://www.digikey.com/product-sear...nSort=1000011&stock=1&quantity=1&pageSize=250

    You'll need to intercept the left and right audio signals by cutting the tracks that connect to the two tags at the fully clockwise end of the volume potentiometer. Connect the socket contacts to the potentiometer pins, and the switched contacts to the tracks that used to connect to those pins. The "tip" connection is the left channel. And connect the shield contact of the socket to the 0V rail at the fully anticlockwise end of the volume potentiometer (the two tags at this end should be already connected together).

    Use stereo shielded cable from one jack plug (at the head end) to another jack plug (to plug into the MP3 player). If the MP3 audio is too loud and you have to turn the digital volume control way down, and/or the audio is noisy, you can add a two-resistor audio attenuator in each channel of the cable. You may be able to fit these inside the headshell at the head end if you use tiny resistors. Use around 33 ohms between the signal wire (from the MP3 player) and the tag of the plug, and a lower value from the plug tag to the plug sheild; duplicate for the other channel. Start with around 6.8 ohms; increase for louder audio; decrease for quieter audio.

    If there is interference, especially from the car engine, don't charge the MP3 player from the cigarette lighter while it's plugged into the head.
     
  4. DoubleDogDan

    DoubleDogDan

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    Jul 20, 2014
    Thanks for the great replies! I've just recalled that the head unit does not have a "regular" potentiometer for the volume control, but a switch which rotates continuously "up & down", so I'm guessing it's digital. My electronics education was in the late '70's, and I'm not familiar with this design, but I'm guessing the "amp input is the center of the pot" probably isn't applicable here, and that this switch sends pulses to some digital entity which adjusts the signal level. Does this fact provide any other options? I do have full schematics of the head unit.

    Thanks again,

    Dan
     
  5. Gryd3

    Gryd3

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    If you have a complete schematic of the internals, we can take a peek and see what can be done.
     
  6. DoubleDogDan

    DoubleDogDan

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    Jul 20, 2014
    Thanks for the offer, here's a .PDF of the schematics in the repair manual: http://j3jlk31uw6.1fichier.com/ If you go all the way to the bottom, you'll see the DL button. I've used this sharing site before with no trouble, I hope it's OK to use it here. Tried just UL'ing the .PDF here, but it's too big.

    Dan
     
  7. KrisBlueNZ

    KrisBlueNZ Sadly passed away in 2015

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    OK. It's pretty easy to hack it into any of the inputs to IC201, the input selector and volume control IC which also provides front and rear outputs from stereo input sources. I've assumed you want to hack it into the radio signal. The mod is on the "Main Block" section of the schematics, in the highlighted area:

    orientation.png
    The mod is shown in the highlighted area. There are two track cuts, marked with "X"es, and five connections to the stereo jack socket.

    mod.png
     
  8. Gryd3

    Gryd3

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    How are you with electronics?
    I can see a couple of spots that a signal can be injected... I really want to know the communication protocol of a CD-changer as that looks like my ideal insertion point...
    You are looking to have your own aux input automatically switch on when you connect a device.. correct?

    Good catch Kris.
    Would he require a buffer to be able to tap into that IC like that?
    I cannot read the part number.
     
    Last edited: Jul 21, 2014
  9. KrisBlueNZ

    KrisBlueNZ Sadly passed away in 2015

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    Good idea Gryd3. It would be great if he could hook into the CD changer audio and do it all properly, with proper protocol support as well. It sounds like quite a job though, which is why I suggested the crude mod.

    No he wouldn't need a buffer, especially if he's driving it from a headphone output from an MP3 player.

    I can't read the part number of the input selector and volume IC for sure either. It looks like YEANSN761026 to me, but that gets no hits on Google. I think it's a manufacturer-specific part number. It could be an externally produced IC that they've badged with their own part number, or a custom IC made specifically by (or for) that manufacturer.

    Dan, can you find IC201 on the circuit board and post all the markings on it please?
     
  10. Gryd3

    Gryd3

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    Simplicity sake, intercepting the audio lines from the radio would probably be the best bet.
    Without knowing how the head unit will react to a CD-changer being present... and if you can get away with a simple dummy communication to 'enable' the input but not actually transmit or receive data. (current disk / track / playtime)

    I wish I could have one of these for my wife's head unit
     
  11. KrisBlueNZ

    KrisBlueNZ Sadly passed away in 2015

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    LOL :) So you could switch her from the talkback station to the easy listening MP3 stream?
     
  12. DoubleDogDan

    DoubleDogDan

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    Thanks so much for your efforts, I'll look through the schematics etc. & see if I can pull this off. I'm actually not too concerned about that, my knowledge of components is a bit dated, but I've always been adept with a soldering iron! What I'm really not looking forward to is pulling the bloody thing out of the car! ;-/

    Dan
     
  13. DoubleDogDan

    DoubleDogDan

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    Jul 20, 2014
    I just noticed the questions regarding the IC number. Here's the entire service manual, with numbers & pinouts: http://8yk8skmm0e.1fichier.com/ Haven't pulled the radio yet, so I can't look at the chip. Thanks again for the great input!
     
    Last edited: Jul 22, 2014
  14. KrisBlueNZ

    KrisBlueNZ Sadly passed away in 2015

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    OK, IC201 is a YEAMSN761026. It's a four-input stereo input selector with volume, tone, and front/back fader. There's nothing special or important about it.

    CN401 on the back panel connects to the external CD or Minidisc changer. According to the interesting but incomplete information at http://www.mictronics.de/projects/cdc-protocols/ several different manufacturers use the same connector for the external changer (a 13-pin mini-DIN type connector), but the pin allocations and protocols are all different! Brilliant :-(

    That page doesn't cover the Mitsubishi version, which they call "M-bus" (not to be confused with two other M-buses - one for SPARC workstations and one for power metering equipment, according to Wikipedia), but it has some public discussion which you might want to read.

    This "M-bus" has three signals called M-SCK, M-BUSY and M-DATA. There is an interface circuit between the connector and U601, the CPU. The signals at the connector all appear to be active low with pullup resistors, so they will form a bidirectional serial bus like SPI with the M-BUSY signal used for handshaking.

    I've tried a Google search on m-bus mitsubishi cd changer protocol but couldn't find any details, so I assume it's proprietary and no one has reverse engineered it yet. You'll have to wait until someone with the right skillset has the right equipment (a Mitsubishi head and a compatible CD changer) and the right motivation to reverse engineer it.

    So we're back to the simple solution of intercepting the audio from one of the standard sources. I suggested intercepting the radio input, so you could still use the built-in CD player, but you could intercept the CD input if you would rather keep the radio available. The other two input sources are the CD changer, which you can't use because the head will not select it unless it thinks there is an external changer connected (which it will determine via the M-bus) and an input for beeps, which is only enabled when the head wants to beep at you for some reason.
     
  15. DoubleDogDan

    DoubleDogDan

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    This all looks pretty straightforward, thanks to the guidance here. I'll try to pull the unit this weekend & will see how it works out. I really appreciate the advice, and the time it took to lay it out for me!

    I've used Digikey in the past, also Mouser & MCM electronics, but it's been awhile. Aside from Digikey, are there any other good component sources you recommend?

    Dan
     
  16. KrisBlueNZ

    KrisBlueNZ Sadly passed away in 2015

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    Digikey and Mouser are the biggest, AFAIK.

    I couldn't say whether they're good or not, but here's the rest of my list:

    Fry’s Electronics http://www.frys.com/ More products than components
    Futurlec http://futurlec.com/ Also has PCB manufacturing and other services
    Newark Element 14 http://www.newark.com/
    Jameco http://www.jameco.com/
    Allied Electronics http://www.alliedelec.com/ US affiliate of rs-components
    Full Compass http://www.fullcompass.com/ Pro audio/video; lighting; musical instruments
    Radio Shack http://www.radioshack.com/ Limited component range
     
    Gryd3 likes this.
  17. Gryd3

    Gryd3

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    Can we sticky an electronics supplier list somewhere?
     
  18. KrisBlueNZ

    KrisBlueNZ Sadly passed away in 2015

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    Yes; I'll make it a resource. It doesn't really belong in any particular forum.

    Edit:
    https://www.electronicspoint.com/resources/component-suppliers.34/
    Input welcome. Moderators, feel free to edit. Others, PM me or post in the Discussion tab for the resource.
     
    Last edited: Jul 23, 2014
  19. DoubleDogDan

    DoubleDogDan

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    Jul 20, 2014
    Thanks for the source suggestions, here's a place I've used over the years, online & in person, great for surplus http://www.allelectronics.com/

    I pulled the radio, much easier than I expected (didn't have to take the whole dash apart, just remove one panel). But I can't get to the main PCB, because I can't get the CD drive assy out of the way. Looks like it should just drop out after removing the top cover, but it doesn't seem to want to & I'm afraid to force it. Can anyone tell from the service manual posted above, or from experience with newer units (this one's 11 years old, should give you my idea of "newer" ;-) how the drive assy should come out? The rear of the assy is loose & drops down, but the front/control panel side seems "stuck".
     
  20. KrisBlueNZ

    KrisBlueNZ Sadly passed away in 2015

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    Thanks for the pointer to All Electronics; I've added it to the resource. Can't help with the disassembly question though.
     
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