Questions on a problem I am running into with a Behringer Subwoofer

Discussion in 'General Electronics Chat' started by Ih2010, Mar 19, 2016.

  1. Ih2010

    Thread Starter New Member

    Mar 19, 2016
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    Hi guys! I own a Behringer eurolive b1500d-pro sub that I used to use for dj'ing gigs in college. About 18-24 months back I started having troubles where it would only play music through it 20-30% of the time. It was a type of issue where if I could get it to start playing music, it would be good for the entire night. However, getting it to start was a pain in the ass and I could not develop a reliable trick - for example I would play around with it for an hour in my apartment, get it to start playing music, and not lose signal until I turned it off. Hooray! However, I would then take it to a frat house or some such and completely fail to get it to play music. For clarification, it turns on every time and I get the blue power signal - it's the playing of actual music that is spotty. Ok that's the background.

    Now, about 8-12 months ago I tore into the sub, pulled out the motherboard, and starting playing around with it with multimeter I borrowed from my electronics lab. Couldn't figure it out, seemed complex, and I know that I barely troubleshooted - it was just that I didn't know where to begin. Now, I've dug back into the thing and I'm ready to take another crack at it after pulling it apart this morning and examining it for an hour or two.

    It is my belief that a connection was shorted somewhere and that this connection is able to work some of the time, but not very often. This is why I was able to get sound to come out of it once in a great while. I recognize that this assumption has little basis in fact and more based on personal experiences with the device closing in on 2 years ago, but it's all I really know to work with.

    By posting on here I hope not to find the answer to all my problems in a single post - but learn where to direct my attention, what to start looking at closer, what resources I may need to purchase, and overall the level of difficulty of what I'm dealing with. At the end of the day I could probably take this to a repair shop and get it fixed for $100-250, but, for many reasons, I would like to avoid that. I've always had a mild curiosity surrounding electronics and have an Amazon wish list with half a dozen things for ~$75 that would enable me to start working directly on breadboards and motherboards - I just need to press the buy button when I know I can use it productively for a project (like this one!).

    Anywho, hope I'm posting this in the right place. I've got part numbers, pictures, several (possibly irrelevant, but maybe not) observations - but nothing of substance to enable me to further troubleshoot/investigate.

    Cheers,
    Ian
     
  2. #12

    Expert

    Nov 30, 2010
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    But we don't.
    How about posting some information so we aren't just guessing into the wind?
    ps, an open connection, like a cracked solder joint, is more likely that a short.
     
  3. Hypatia's Protege

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    Mar 1, 2015
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    Web references show/describe the "Behringer eurolive b1500d-pro sub" as a 'powered subwoofer' unit -- Hence your allusion to a 'motherboard' (i.e. the main-board/back-plane of a personal computer system) would seem a non-sequitur (of sorts):confused: -- Please elucidate!:)

    I agree with the previous respondent (@#12 ) -- An 'open' is more likely - a 'short' (anywhere outside of the small signal stages) -- For example in the PSU, power Amp or transducer itself -- would likely cause other issues which, in turn, would likely present as a persistent failure (as opposed to an intermittent) -- Moreover, the probability of said etiology is greatly enhanced in consideration of the intense vibratory conditions inherent to such a device...

    As per post #2 on this thread -- please post more info -- we'll be happy to assist your troubleshooting efforts!:)

    Best regards
    HP:)
     
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  4. Ih2010

    Thread Starter New Member

    Mar 19, 2016
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    Mostly because I was on my phone writing this up so far and re-learning what I learned in the past. Uploading pictures now and will edit this post with more info shortly. Apologies I didn't include it in OP, 'tis a lazy Saturday afternoon for me! :)
     
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  5. Ih2010

    Thread Starter New Member

    Mar 19, 2016
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    It would appear that I am unable to edit my previous post. Not sure if that is a restriction because I am a new account - but in either case sorry for the double-post. The album is made and I hosted on imgur, I could directly link the pics here but since I've got 14 images on it I'll just leave this here for thread cleanliness: http://imgur.com/a/u22y6

    Explanation of potentially more important images:

    1-3 show about a third of the board each from a top-down view
    4 highlights a little mark that a friend pointed out in that it looked different from the other places on the board where these same parts are - but it may be just that it's some sort of solder/glue
    5 is my basement saying hello and showing a rough size of what I am dealing with. Yes, I have anti-static gloves and none of this ever touches the carpet you are seeing
    6 and 9 are closer looks at the bottom piece below the main board. This is where the power gets plugged in and a switch is pressed in to turn the device on
    7 looks at the board from what would be the top if it was in it's typical standing position. Get's some view on the bottom half of the board
    8 also gets a bit of insight to the bottom half of the board, but from the side rather than the top. Not sure how useful 7/8 really are.
    10/11 show, with flash on, more views of the middle/bottom part of the board
    12 starts focusing in on the toroid (what a cool little device!!!!)
    13 - Before these pictures were taken, there was some plaster/battery leakage (My friend who spent 20 minutes looking at this with me thought it was possibly a battery leakage until we learned what the purpose of the device is) - Now after removing it with some isopropyl and a q-tip and I see how moveable the piece sticking out from the middle is I wonder what the purpose, of what I believe was plaster, was for. I am concerned this will turn into a problem moving forward if I can fix the initial break.
    14 - A closer look at the resistor/capacitor poking out from the middle of the toroid. It doesn't look like it belongs there at all and I am confused by it's existence in that place.

    I would be more than happy to take more, and possible more accurate, photos to help further the inspection of this little piece. The board does say SMPSU28 on it in 2 places, so am wondering how accurate the schematics are for the class-d circuit posted on the only reply in this thread (Looks complicated enough!). Also, this thread looks very useful in that someone has a similar model amp with some problems that also uses the infamous class-d amp. My electronics never hit a mastery level and it's rusting over with no use in 2 years so I'm concerned I will not be able to pull enough potentially useful information out of that thread. Hmm. But, I am determined and do not want to give this up!

    And also! In response to the last reply, yes I believe 'motherboard' is not the right terminology, however it's the closest comparison to what I am looking at that I am familiar with. If it's an open, what are some steps to diagnose where/why/how it is occurring? I would be happy to read any documentation/procedures and/or would love to dig for this info in a different subforum if that information is around somewhere. Thank you for the quick responses!
     
  6. #12

    Expert

    Nov 30, 2010
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    :(A massive Bass amplifier that is almost completely surface mount.:(
    You're going to have to start with the tap-tap wiggle-wiggle looking for an intermittent connection.
    If that doesn't work, this will need a schematic and signal tracing. That is not a job for an amateur.
     
  7. crutschow

    Expert

    Mar 14, 2008
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    Would the word "main board" instead of mother board be more appealing to your pedantic nature? :rolleyes:
     
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  8. Ih2010

    Thread Starter New Member

    Mar 19, 2016
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    I'm the type of person who enjoys jumping into a volcano and trying to dig my way out rather than be feared away due to being an amateur. I'm at least not a complete novice when it comes to electronics, but the more I read and learn the more I am getting nervous this will be a complete waste of my Saturday :/ Hmm.

    Other observations/notes:
    I've tried the wiggle wiggle approach when this problem first started occurring with the connections on the sub of the cables that run between itself and the speakers and I vaguely recall having some success with that initially. As time went on it became more and more difficult to reproduce and eventually was impossible. I am unsure what I could have wiggled to make that happen. Also, and this was more common, I would leave the sub plugged into my system while it was not working and anytime between 15-90 minutes after I started playing steady music the subwoofer would 'pop on' and then work nominally until I killed the power to the sub. I definitely noticed some odd patterns when I first began having this problem but, alas, it was quite some time ago and many of those patterns deteriorated into the device simply not working at all.

    Other random tidbits that I've found:
    I have 2 IRS20955S MOSFETS on the board - found this data sheet that explains a lot about them: http://www.irf.com/product-info/datasheets/data/irs20955pbf.pdf

    I also found a general tutorial on class d amps from irf: http://www.irf.com/product-info/audio/classdtutorial.pdf

    My problem with both of these is that I am not an electrical engineer, merely a network engineer, and I am hoping to fix this unit without becoming a full-blown electrical engineer (yet :rolleyes:)

    Edit to #12 about it being a surface mount: I have not tried this yet for fear of breaking something and no gameplan on what to do if I did it, but I do believe I can dismount both boards from the heatsink it is attached to in order to get at the back. But then my question becomes: what do I gain with access to the back?

    Also, as another addendum, I do currently have one of these multimeters
     
  9. #12

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    Nov 30, 2010
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    That's what I said when I took my fathers pocket watch apart.:D
    You are thinking about doing this in one day?
    You're going to need some luck.
    We just had a guy spend 2 weeks on a kitchen blender that only had 22 parts.
    http://forum.allaboutcircuits.com/t...t-show-signs-of-damage-by-overheating.121336/
     
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  10. Hypatia's Protege

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    Inasmuch as 'mother board' is jargon exclusive to IT hardware, 'main board' is a definite improvement all around -- Still...:confused:
    I apologize that my 'call for clarity' was perceived as pedantry -- I'm certain we may agree that ambiguity is best avoided in any event but especially on international fora?

    Best regards
    HP:cool:
     
  11. #12

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    Nov 30, 2010
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    Anybody who works on these or looks at the photos knows that there is only one board in there. The owner can call it the elephant board for all I care, and there will be no confusion as to which of the one boards he is referring.
     
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  12. Hypatia's Protege

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    Mar 1, 2015
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    @Ih2010

    FWIW -- As a preliminary, please try this:

    Power the unit on, apply a signal to the input, then with the 'blunt end' of an all plastic ballpoint pen (or similar non-conductive implement) carefully apply pressure to various points on the board (being very, very careful to avoid mechanical damage to the smt components)...

    Best regards and good luck!
    HP:)
     
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  13. Hypatia's Protege

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    Inasmuch as both you and the TS are native English speakers (or, at very least, masters of said language) such usage indeed poses no problem!:) That said, these fora are frequented by many 'ESLers', etc, whom may find such usage confusing --- Moreover, the original post presented no images -- It is not unreasonable to assume that a piece of audio equipment may contain a dedicated/integrated 'PC' as do certain (musical) synthesizers --- FWIW It was not my intent to 'correct' of the TS -- My remark was a genuine request for clarification:)

    Best regards
    HP:cool:
     
    Last edited: Mar 19, 2016
  14. Kermit2

    AAC Fanatic!

    Feb 5, 2010
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    I clearly see that your post is written in english HP,
    But,

    What?
     
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  15. Ih2010

    Thread Starter New Member

    Mar 19, 2016
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    This was an excellent place to start, although it did not solve my problems. After 10-15 minutes of probing with no luck I thought to myself "I hope I didn't grab my broken xlr-xlr for the connection between my sub and speaker"...popped it off and sure enough it was the broken one. Damn you Murphy!

    Reversed the connections so that the audio 'input' from my 3.5mm to XLR was in input A of the sub. I then hooked up an xlr-xlr from both the output-A and throughput-A connections to the speaker (Which serves as a signal passthrough) and I got audio out of the speaker and an occasional 'hiccup' from the sub every 15-20 seconds. This 'hiccup' is consistent and happens at a regular interval, not really sure how else to describe it though. It's almost like the sub wants to cut on, but then it gives up because it's unable to. I also find it interesting that the passthrough works in every way on both A and B - there are 4 possible connections (when signal gets sent to sub and then to speaker) to get sound based on how I am hooking it up. This makes me believe the top most part of the board (which handles signal passthrough and sound modulation I believe) is not having troubles, but something about the actual amplifier is.

    I think the hiccup is important. As consistent as it is and as often as it happens I think my answer may lie in tracking down the root cause of the 'hiccup'.
     
  16. Hypatia's Protege

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    Touché! Typo corrected!:)
     
  17. Hypatia's Protege

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    That would appear a reasonable assumption!:)

    FWIW: The described symptom smacks of a 'decoupling issue' (perhaps indicative of a failing Cap or resistor) --- Some 'voltage' readings of the PSU rails at various stages may be useful -- In case you ignore the correct values, you may 'hunt' the difficulty merely by 'looking' for EMF variation in 'sympathy' with the period of the 'hiccough' cycle...

    Best regards -- and best of luck!
    HP:)
     
    Last edited: Mar 19, 2016
  18. #12

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    Nov 30, 2010
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    It is entirely typical for a power supply to keep checking to see if it is safe to come on. (Self-protecting power supplies is one of my specialties.)
    That hiccup is probably a symptom of a shorted power stage. The power supply might not be broken at all.
     
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  19. Hypatia's Protege

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    @#12 makes an excellent point!:) -- Please bear in mind, however, that should the 'hiccough' symptom indeed owe to PSU cycling, such represents 'advancement' of the original difficulty or a 'new' malfunction perhaps due to an over current condition inadvertently introduced during disassembly? - Please inspect leads, connectors, etc against the later possibility... Note also that audio power amplifiers not infrequently feature similarly acting mismatch (i.e. over/under load) protection...

    Best regards and again good luck!:)
     
    Last edited: Mar 21, 2016
  20. Cartel

    New Member

    Dec 1, 2016
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    Hello I am working on this behringer model too.
    Same thing, a thumping pop every 5-10 seconds.
    I seen right away some garbage capacitors behringer used, decon and ksd....junk.

    all the 470uf in one section of the 15V supply were buldged and tested 50pf.
    I replaced them all and now I still hear nothing, no thump but a screeching after a bit.
    Voltages all seem good, the big diodes and IRFB4227's test good.
    I have a schematic of the 1800 thats pretty much the same.
     
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