EEVblog Electronics Community Forum
Electronics => Repair => Topic started by: pnoaiwevun on February 20, 2019, 12:44:25 pm
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Hi all,
I have a pair of Audioengine A2 (not A2+) active speakers that stopped producing any sound between one use to the next. I tried different power supplies, outlets, input sources, and input cables, all without any sound. The right speaker is passive and does work when hooked up with another set of speakers. The company does not service the product anymore and gave a 50% discount for a new set of speakers, so I am trying to repair these as a learning experience.
After opening them up, the only potentially obvious issue I see is the hard black substance that spread across the top of the circuit board (photo attached). I haven't found a similar substance in Google searches but find references to black substances that are epoxy or potting compound (or leakage from a blown component). The way it is spread across the board does not look intentional, but I'm no expert.
My idea was to try to convert these to passive speakers and use an external amp. My searches online have led at best to forum posts about the larger Audioengine A5, but with my lack of electronics knowledge, I haven't been able to find a way to get started. Your advice about how to work on this -- or suggestions for other resources to look through -- would be most welcome. Thanks in advance!
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I seem to recall Dave doing a video on this kind of problem, have a look around...
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Looks like intentional potting to me, and the issue Dave ran into was that the particular potting compound used collected water as it aged, causing problems under it - with a properly selected compound, this wouldn't have happened.
There's a chance that it's the cause or that the cause is under it, but I would suspect other more common causes before jumping on the potting compound. Start with the power supply, then especially if you have a scope, trace through the signal path to see what's operating.
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The gunk in my case seems non-conductive, so I imagine the problem may lie elsewhere?
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Have you checked to see if there are any voltages on the PCB ?
What part number is on the amplifier chip on the heatsink ?
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I'm sorry, I haven't been able to find out if there is any voltage on the PCB. Is there a certain place I should attach the multimeter?
It looks as if the characters on the heatsink are DA 7265B CZOLP020 VW CZ MAR (some are hard to read).
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OK, it looks like the amplifier chip is a TDA7265B. https://www.st.com/en/audio-ics/tda7265b.html (https://www.st.com/en/audio-ics/tda7265b.html)
Measure the voltages on pins 1, 3, and 5 of the chip with the multimeter +ve (red) probe. Download the data sheet so you know where the pins are.
For each measurement, the multimeter -ve (black) probe will be on the circuit ground. The shield of one of the RCA sockets will do for that.
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Thanks! I’ll give it a look in the AM and let you know.
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I used the diagram of the pins for the unit (attached). I touched the outside of the RCA port with the black (IMG_0028) and contacted what I believe to be the first, third, and fifth pins with the red (IMG_0029, -30, and -31). I got similar readings for each (IMG_0032, -33, and -34) of around 17 when the dial was set to 20V direct current. But I am unsure whether I had the multimeter dial set to something else.
As an aside, the white substance around the unit is very soft (IMG_0029-31) and came off on the multimeter when touched. I don't know if that is supposed to do that.
I may have to post some of the other pictures separately, since the file size is too large.
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The second set of photos:
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The third, final set of photos:
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The white stuff is heatsink compound and perfectly normal to be there.
Pin 1 is power -ve so the -17V seems ok. Pin 3 is power +ve so the +17V seems ok.
Pin 5 is the mute line and should be close to zero volts when operating correctly. This seems to be a problem.
Judging by your posts, I'm not sure you have the skills to diagnose this repair any further. I'm certain that I could repair this unit in person, but without a schematic of the whole unit it would be very difficult to do via posts and pictures.
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Thanks, David. You're probably right that I don't have the skills for this. :) I may have to just give up and take it somewhere. (you don't happen to live in the NYC area...?)
Do you have a general guess at whether there's a specific component that needs repair -- or is it too hard to say without seeing the speaker in person?
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Removing transistor Q1 may allow the unit to work again (as a test), but you may find it fiddly to remove (and test) without damage.
Maybe measure (resistance range on meter) the 15K resistor (marked 153) that goes to pin 5 of the audio amp chip. Do this with the power off.
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Thanks!
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I have the same set of speakers, but my problem was that my left channel was significantly softer than the right. The potting compound is a pain to remove, but I managed to remove most of it to expose the PCB. I initially replaced the TDA7265B straightaway, hoping for a quick fix but that didn't work. So the problem most likely lies within the pre-amp section which is powered by a NE5532 SOIC. The left output here is also lower than the right, I am not sure if it's the op-amp, or the passive components around it. Without a schematic, it's going to be very hard to troubleshoot. I've since put it aside till I can get more time. From what I can gather, it appears that many AudioEngine speakers have this or a similar issue.
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Are there any pots or volume controls anywhere in the circuitry? Might be worth a try to treat them to some Deoxit.
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There is a volume control on the left speaker - I don't know how it connects in the circuitry. Since there's no sound at any volume level, I suspect the problem lies elsewhere?
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Here's the video that SilverSolder mentioned, which might be very relevant in your case.
https://youtu.be/dftkoD7LG0A
9:45 might be the relevant part, if you don't want to watch the whole thing, but I would recommend you watch it all, it may help you troubleshoot yours. :)
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Thank you!
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Old thread, but solved.
**There is a bad TRACE to PAD connection on what would be called the component side of the PCB at the connection to the VOLUME pot SWITCH.** Scrap away the black goo and RESIST and solder the switch terminals to the now exposed traces.
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Thanks for the reply! I ended up giving them to my friend, who rewired them to make them passive.
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Hi, have the same problem with low volume on Left speaker
Please, can you explain what you mean with "Scrap away the black goo and RESIST"
Thanks
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Hi, have the same problem with low volume on Left speaker
Please, can you explain what you mean with "Scrap away the black goo and RESIST"
Thanks
The resist is the green coating, like a thin lacquer. You need to scrape that off to expose the metal track where you want to solder.