Wednesday, November 21, 2012

Resurrection of a Bose SoundDock iPod dock


I'd like to begin this blog by sharing something both useful and nerdy. Something about music and science and perhaps environmentally conscious at the same time...

Well, I was given a broken Bose SoundDock a while back.  It went "shhhhhhhhhhhhhhhhhhhhhhhhh"-(silence) when turned on.  The "sh" noise lasted only a few seconds.  No music, no sound once it fell silent.  Given the option to fix it and keep it or throw it away, I figured it might be worth fixing this beast (priced at ~$230, but worth nothing as delivered).

In this first post, I'll tell you about how I turned this trash into treasure.

Patents

Incidentally, while I was reading the label to figure out what this Bose product was officially named, I couldn't help noticing U.S. PAT. NOS 7,277,765 and D514090 on the bottom.  Thanks to Google's great Patent Search, I could have a good laugh at the bullshit contained in these documents.

The second one, "Sounds system for portable music player," is a design patent and makes just a brief claim:

The ornamental design for a sound system for portable music player, substantially as shown and described.

It contains several figures which I suppose secure Bose's design IP, including FIG. 1 shown above.  Such short claims do not seem unusual for design patents, such as those for this popular beverage maker, hideous but somehow unique grand piano designs 1 and 2 (good one Zeiser, Mr. Von Rohl will be really upset he didn't think of that!), and the curved body of cheese made of offset slices of cheese... yeah.

The first patent "Interactive sound reproducing" contains a little more content.  Its abstract describes something about an audio system that attaches to a computer...

ABSTRACT
An audio system attachable to a computer includes a sound reproduction device for producing audible sound from audio signals. The sound reproduction device includes a radio tuner and a powered speaker. The audio system further includes a connector for connecting the sound reproduction device with a computer. The computer provides audio signals from a plurality of sources, the sources including a computer CD player, digitally encoded computer files stored on the computer, and a computer network connected to the computer. The sound reproduction device further includes control buttons for controlling at least one of the computer CD player, the digitally encoded computer files and the computer network.
Let's see if this makes sense with what I know about the SoundDock:
  • "attachable to a computer" > you can stick your iPod onto its connector, I guess.
  • "producing audible sound" > not anymore!
  • "includes a radio tuner" > not that I'm capable of finding.  You?
  • "powered speaker" > check.
  • "connector" > iPod connector, yes.
  • "audio signals from a plurality of sources" > yes but not the CD source (thanks for killing the CD, Apple).
  • "control buttons for controlling at least one of the computer..." > it seems to me like there are only volume buttons.
Well, those patent claims are dubious... but so is the functionality of their product!  Ok ok, on with fixing it...

Diagnosis

The first step when trying to fix electronics is to open them up and check for things that look broken.  Pretty obvious, but you should be aware of this: electronics run on smoke -- they will continue to operate normally until they have released all of their smoke.

The telltale signs of smoke leakage were obvious on the main board in the bottom of the unit:


The affected IC was made by International Rectifier and probably does some power reg function or other.  At any rate, the part number was totally burned off and rendered unreadable.

My guess was that the big computer-y looking chip with the bajillion pins on it did something smart and complicated and that I would have very little hope of fixing this board.  This computer-y chip probably talked to the iPod and allowed the control of its volume output or something relatively useless with regard to basic audio amplification functionality.  I thought that somewhere deep down in this SoundDock, there would have to be some simple amplifier whose workings I could understand and whose analog input I could just highjack.

Pulling off the front screen and unscrewing the heat-sink panel that lies between the two speakers, I found the board with the power amplifier on it.

The amplifier is a Philips TDA8922 2x 25W Class D power amplifier.  (Class D amplifiers achieve high efficiency using a neat pulse width modulation scheme)

Consulting the Data Sheet for the TDA8922, I noticed that pin 6 was a "MODE" pin used to select standby, mute or operating modes.  This is a common feature in Class D integrated circuit amplifiers since it allows them to be turned on/off by some control voltage to save on standby power.  I looked for the existence of a "MODE" pin because the "shhhhhhhhhhhhhh"-(silence) behaviour tipped me off: the power amplifier was clearly not broken (it made a "shhhh" sound), but something might be turning it off -- perhaps the smokey computer-y circuit discussed above.

Holding an oscilloscope to pin 6 showed that the voltage was around 5V while "shhhhh" came out, and then it dropped to 0V.  The MODE pin controls three regimes of operation:
  • Standby 0V - 0.8 V 
  • Mute 2.2 - 3 V
  • On 4.2 - 5.5 V (maximum voltage tolerated by MODE pin = 5.5V)
The strategy I had in mind for fixing the SoundDock by this point in the diagnosis was
  1. Remove the connection to MODE pin 6 and allow it to be controlled manually by a switch (i.e. force the amplifier into the operating mode)
  2. Figure out where the analog (music) voltages are in the circuit board and make them accessible by a connector.

Fixing it!

Mode Pin

I checked if forcing the MODE pin to be "on" helped by constructing this voltage divider to provide 4.9 V to pin 6.


The input impedance of pin 6 seems to be on the order of 5.5 kOhm = 5.5 V (max input voltage) / 1 mA (max input current).  The Thévenin Equivalent resistance of the above circuit is 0.36 kOhm (if I calculated it properly), so it should be able to supply enough juice to drive pin 6.

Here's what the resistor divider test apparatus looked like.


The red wire connects to pin 6 (the leg of pin 6 was ripped up with the help of a soldering iron and some tweezers so as to be disconnected from the original printed circuit board signal).  The resistors connect to +18 and 0V pads that I happened to find nearby (see description of J601 later on).

With the resistor divider in place to force the amplifier to be "on", I touched audio input pins 4/5 and 8/9 with some tweezers -- sure enough the amplifier clicked and buzzed, so it worked.

Finally, I transplanted this resistor divider near the power entry on the main board and took the red wire 4.9 V output and connected it via a switch (shown later on) to pin 6.  (if you want details on how to do this, let me know and I'll take it apart again and take extra photos... I'd feel honoured if you were interested in it)

Audio connection

The Philips TDA8922 has analog inputs on pins 4/5 (+/- in) and 8/9.  5 and 9 seem to be referenced to the circuit ground, so effectively, we are looking at connecting audio signal to pins 4 and 8.

These audio signals travel from the main board (with the fried chip) to the power amp board (seemingly working) through a flexible flat cable.  The connector on the main board is J601, for which I have mapped out the following connections:


After identifying locations on the main board corresponding to the L audioR audio, and ground signals shown above, I soldered some wires to them in order to inject some audio from a 3.5 mm headphone jack to be added to the front panel.  Here, blue = LEFT, red = RIGHT, black = GROUND.  Note how I cut the printed circuit board traces for the original L and R signals coming from the computer-y chip... follow from the point at which the wires are soldered and move slightly to the right - the traces are cut using a sharp knife.


The Result

Here's a view from the bottom of the modified SoundDock:
On the left, you can see a switch which manually sends 4.9 V to the MODE pin of the Philips TDA8922 to put it in "on" mode.  This is useful so that the speaker system can be turned off when plugging/unplugging things from the audio input to avoid loud clicks.

On the right, I have installed a 3.5 mm headphone jack which brings the left, right, ground (BLUE, RED, BLACK wires) to the places you saw above to inject audio signals into the circuit board.

The front panel of the BOSE unit had just enough room under the base to accommodate the new switch and jack... almost like it was built for this in mind ...

Final Notes

It's been working perfectly well for the last 4 months.  It's worth noting that the original iPod docking connector still works for charging, but since I disconnected the audio connection from the computer-y chip, it can't play audio through that connector anymore.  Another issue is that there is no volume control - you must be able to set the volume on the device you're connecting to it (a minor hassle).

One could consider wiring up the analog L and R audio pins from the iPod connector to the same place I showed above for the 3.5 mm jack.  This would allow for full music playing functionality via the attached iPod / iPhone - but you'd still have to set the volume on the device itself.

So far, I've found the 3.5 mm jack to make this unit more useful than it was originally designed to be:  I can plug in a laptop or iPad or other analog audio source now!

In the future, I might venture into adding a volume control knob on the front panel.

For now, I hope this helps you save a few tons of COemissions by giving new life to that decent sounding but completely broken SoundDock you might have lying around.

33 comments:

  1. I have a bose sounddock series 1 and the ipod dock pcb brike, im having trouble setting up this modification can u please show me more details on were to solder the resistor divider and power switch and im also having trouble finding were the aux inpur will be soldered on too? Can u please show me more details and steps on how to do this?

    ReplyDelete
    Replies
    1. Hi, sorry I never saw this until now! For the resistor, see the details of J601 pins and you'll find the +18V and ground there. Anywhere you can pick up the +18V power and a ground will be fine for the divider as pictured. The switch can just interrupt the signal to Pin 6.

      For audio, see J601 as well. You just need to pick up L, R, and ground somewhere on the board. Find the L and R from J601 and trace them out on the board-- you can solder to them wherever convenient.

      Delete
  2. Hi William,

    Also received a broken sounddock similar to yours but it was exposed to rain before I received it.

    Am new to electronics repair so would appreciate any tips specific to the sounddock. Also if interested I can send you photos.

    To date I have taken it completely apart and am now checking for water damage.

    Thanks

    Ken

    ReplyDelete
    Replies
    1. Yikes... water .... I have no idea what you're in for ;) good luck

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  3. could you recommend a suitable pot for the volume control,thanks

    ReplyDelete
  4. great write up, many thanks.

    ReplyDelete
  5. Thanks a lot can you please tell me what kind of resistors did you use thanks

    ReplyDelete
    Replies
    1. any old 1/4 watt resistors will do fine.

      Delete
  6. Hi William,

    The "affected IC" is a F7103 (from IR, you're right).

    Mine doesn't seem to be out, but the pin 6 voltage also dropped to 0 volts quickly (I can hear music during les than 1 second).

    Is there something else to check on the board to determine any other failure ?

    Thanks in advance

    ReplyDelete
    Replies
    1. Ok I found it :

      As you can see here [http://pinouts.ru/PortableDevices/ipod_pinout.shtml], pin 18 of the Apple 30-pin connector is the HPD "Hot Plug Detect" port which provides 3,3V to power ON the SoundDock.

      Delete
  7. Terrific writeup! It's been quite some time since you posted it, but do you happen to know whether the small pcb that contains the ipod connector is necessary for the unit to function? I intend the transplant the internals to a custom wooden box.

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  8. Hi,

    You can forget the resistor divider and find 5V directly on the board.

    Provide voltage to the MODE pin is only recommended if your 7103 chip is out, try to search "sounddock pin 18" on Google.

    The iPod connector PCB is useles, mine doesn't have it.

    I also didn't cut the printed circuit board traces and I didn't rip up the pin 6, and everything goes well.

    ReplyDelete
  9. If that is the case, can the main board be omitted? And by that I mean the board that connects to the 4-pin power supply. Ideally I'd like to have the main philips amplifier board, speakers, and an aux input for the build.

    Perhaps even add a potentiometer to control volume if you can instruct me on where to put it.

    ReplyDelete
  10. Hm, that's a good question.

    Maybe you can try to inject power supply and audio inputs directly by the flex cable (J601, as William Paul mapped it).

    About the potentiometer, it seems to be easy, take a look here : http://tinyurl.com/qd85lze

    Dx.com products look cheap and clean.

    Keep us updated !

    ReplyDelete
  11. Although no big progress, i was able to get audio with the steps on this page. Everything still works as it should which is great!

    Next step is to try and bypass the secondary board. That way I can transplant it to run off of 5x18650 laptop cells.

    Will report back.

    ReplyDelete
  12. hi

    i did the above process, the input from 3,5 is not working unless i keep iopd on the dock, if i remove the music stops.

    ReplyDelete
  13. hi

    also if i supply 4.9v to PIN 6 then the dock is muted, so in order to play music i have to disconnect the resistors.

    is there any other way to stimulate the connection of ipod to dock so that the input from 3.5 woks like another amplifier.

    pl help. i have already spent a lot of time and still cannot achieve what i need.

    tx

    ReplyDelete
    Replies
    1. Your PIN 6 seems to behave oppositely to what normally happens... I'm really not sure what to recommend :( sorry...

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  14. The pins are epoxied in, but I hope these images help.

    http://i66.tinypic.com/2wcjimb.jpg

    http://i64.tinypic.com/o6a04y.jpg

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  15. Hi Marti,

    Can u please tell me if still remember the transistor ID that also been burnt. I also got the same issue. Thanks a lot

    Dexter

    ReplyDelete
    Replies
    1. Something by International Rectifier but it wasn't legibile

      Delete
  16. This comment has been removed by the author.

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  17. Hi, good guide for audio aux. Is there a way to regulate a 5v USB power supply from this? I'd like to power a Chromecast audio directly from the Bose unit. Thanks

    ReplyDelete
    Replies
    1. There is probably a 5V rail supplied somewhere in the original ipod dock connector... I didn't search for it... (maybe look up those connector pinouts)

      Delete
  18. How does it sound now in comparision with an original sounddock with working DSP?

    ReplyDelete
    Replies
    1. Good question! I actually got this unit from my mother in law after it broke.. :P ... so not sure... It sounds good enough that I'd believe that's how it was designed to sound, but I really don't know how much the Bose engineers would have tweaked things in their DSP that I bypassed.

      Delete
  19. I've reading this and other articles and have been thinking about modifying my faulty Bose Sounddock Series 1 A to use a "12V LED Bluetooth Stereo MP3 Player Decoder Board which has SD/USB/AUX/FM plus Remote Control" these boards are only a few Dollars on ebay. The 12v can come from Firewire pin on the ipod dock. I would ideally like its output (L, R, GRD) to go directly to the Amp board and bypass the DSP processor board. Have you any thoughts?

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  20. Good write up and more info than I could ascertain from elsewhere! I had a broken SD come to me with the DSP board as the main suspect. None of the people (Invebo or eBay) would provide any clues as to the root cause. However, using your pin-outs and some other info for an aux-in elsewhere I was able to check the analogue audio in and bridge it to the amp which worked. Your board appears to have a different layout and components so suspect it is 'Type B' unlike the one I have which is 'Type A' - after a bit of probing I couldn't see any output but I was then trying to test the capacitors (no obvious leakage) and using a 'scope somehow the board burst back into life! So I think the cause may have been a dry joint on one of the electrolytic capacitors which prevented the DSP chip and associated Codec chip (WM8734 in my case) talking to each other to turn the digital side of things on. The whole thing seems to be functioning again now! Thanks again for publishing your findings - it would have been a needle in a haystack otherwise!

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  21. I have a unit that had been junked.It does not have the power adaptor or the 2x2 4 prong connector.
    Any suggestions on how I could improvise, other than buying a $50 replacement.

    ReplyDelete