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Let’s take it apart

One Behringer B2031, Fried

June15

B2031One of my B2031 studio monitors crapped out in spectacular fashion last night. In a pyrotechnic display reminiscent of an arc welder, an apparent failure of the power supply treated me to flashes of light, copious amounts of acrid smoke, tiny drippy bits of melted metal and an aural experience only available when large alternating currents pass through components undergoing transition from solid to gas.

Downside: It’s broke.

Upside: I get to take it apart, see what broke and fix it.

The way these speakers are set up, the amplifier is bolted onto the rear of the unit. It has all the necessary power supply and signal processing gizmos built in. Initially I was concerned about finding serious damage. Upon inspection I was relieved but somewhat perplexed.

The Damage

Relief came in the form of simple blown-out capacitors and a linear power supply. Around these parts, we like linear supplies because, unlike obtuse switching-type designs involving voodoo, they can be fixed. Those blown out capacitors, though, have me confused even as I write this.

One ceramic disc capacitor is connected in parallel to each of the four diodes of the bridge rectifier in order to, as far as I can tell, prevent RF interference. There is no mains line filter on this bad boy and the amplifiers are supplied by the bridge with only a single 6800uF electrolytic for each rail – no further filtering or regulation.

What I don’t know is why or how exactly they failed. If you look at the photo, all the capacitors should be parallel to the diodes – like the one in the top left corner of the  photo. The second one down is leaning, the third one is split and slightly twisted and the lowest one has turned nearly 90 degrees, is missing its lower third and is sitting over the lead of the diode. It isn’t a huge leap of reasoning to assume this is where the fireworks were.

I don’t know if the capacitors simply failed physically from vibration and one managed to break and twist around to make contact with the lead of the diode somehow or if they were under significant electrical stress from poor design choices. I’ve never seen a ceramic disc capacitor fail like this.

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Upon examination of the still-functioning other unit, I found it to be in similar but pre-disaster shape. One of its capacitors showed evidence of arcing and twisting, but the others seemed to be in fair shape. As far as I can figure, this is a flaw in the sizing of components. From what I read here, you want a bypass capacitor 0.01uF to 0.05uF with a working voltage substantially higher than the reverse voltage across the diode. The failed units appear to have a working voltage of 50V and are in a circuit where they are exposed to a voltage around 30V. I don’t feel as though 50V is “substantially higher” than 30V. They were also 0.1uF capacitors, 10 times larger than recommended in that source above. Since I’m not sure exactly how this whole mess acts as a filter, I can’t plug stuff into my own equation and get an answer but I suspect the capacitors may have been too large and passing current all the time rather than just noise leading to heating and failure.

I’ve ordered new 0.01uF capacitors with a 250V rating to replace all 4 in each amplifier. I also ordered four new 6800uF electrolytics and new fast recovery diodes for the rectifier. The 6800uF capacitors on the amplifier that went bad had distended tops and rattled. After pulling them out of the board, they measured about 3300uF each. As for the diodes, FR types are apparently better for rectifiers and who knows how much life is left in the ones that gave the fireworks.

The repair is here.

8 Comments to

“One Behringer B2031, Fried”

  1. On October 16th, 2008 at 8:14 am Alex Says:

    Hi!
    it’s not exactly the same situation for me but i have a failing B2031 too. I was wondering if i could maybe pick your brains for some advice before i pursue the expensive pack-it-up-and-send-it-off route?

    Send me an email if you’re interested at all in helping me!
    Thanks.
    Nice site by the way, some interesting projects 🙂

    alex

  2. On April 30th, 2010 at 1:41 pm Thomas Says:

    Could you possibly list the digikey parts numbers you used? Just so, anyone out there who wants to venture this route on their own knows what to order. thanks

  3. On June 2nd, 2010 at 1:29 pm Ian Says:

    Hi,

    I read you repair article with great interest. I have a pair of B2031s and one of them emits a loud popping sound about 45 seconds after switch on and the limit light comes on. If I turn it off and leave it for a few seconds it then usually works OK. This happens every time. I thought I would take a look inside to see if I am leading up to the problem you described. Although I could not notice any sign of the diodes cooking, I did notice that my unit does not have any of the ceramic capacitors fitted in positions C1, 9, 14 and 20, which are the one you replaced, although the holes are there and the PCB is marked accordingly. I would appreciate any advice you could give as this problem is becoming very annoying.
    Regards
    Ian

  4. On June 2nd, 2010 at 2:23 pm bryan Says:

    Ian,
    It sounds like your problem lies somewhere along the input signal path and not with the power supply. Unfortunately, I don’t know enough specifics about the Behringers to diagnose your problem with any certainty.

  5. On May 3rd, 2011 at 7:07 am Grant Says:

    The replacement pcb from behringer looks like it has different components on it in that part of the circuit.

  6. On March 10th, 2012 at 6:53 pm Chris Says:

    This post is already somewhat helpful, so thank you for it! I have a pair of B2031 monitors that I’ve been extremely happy with for years. Yesterday when I turned them on, one was emitting a VERY loud buzzing. Not the kind of buzz associated with RFI or improper grounding, but we’re talking overpoweringly loud.

    I shut it off immediately and tried different cables and outlets, to no avail. All of this with no signal plugged in. Since it’s long past its warranty days, I decided to take it apart. I don’t see anything major wrong with it, but after reading your post, I noticed one of those capacitors does look mildly charred. It hasn’t exploded like yours, but there is some black on them. There’s also some leaning of the capacitors going on.

    What I’m wondering is, could this be causing the loud buzzing and a precursor to exploding? Or would you think it something else? Just wondering if I have to order some new capacitors and break out the soldering iron, or keep looking for an alternate cause.

    Thanks!
    -chris

  7. On March 10th, 2012 at 7:15 pm Chris Says:

    Well, as usual, I asked a question and then figured it out. After posting my prior comment, I looked a lot closer and, sure enough, found one of the charred capacitors actually had blown a tiny piece out of it. I removed that one and the neighboring one that was slightly darkened and now the buzzing is gone!

    Even though this could probably work just fine without the capacitors, I’m going to order the replacements anyway and fix it properly. But at least now I can keep working in stereo until then!

    Thanks so much!! You just saved me oodles of money I was worried I’d have to spend to repair or replace my beloved B2031!

    -c

  8. On May 21st, 2019 at 8:21 pm Beau Bennett Says:

    Hi, I know this is an old post, but I just found it looking for a repair for my b2301a. 1 of the speakers is turning off after about 2 minutes or so randomly, no matter what power setting I have it on eg – on or auto. The speaker turns on I have read elsewhere on the net about the regulators overheating and a small heat sink screwed on to them has fixed the issue for some people or even replacing the regulators?? Just wondering if I’m on the right track or not???
    Any advice would be awesome, thanks in advance

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