Studio monitor buzzing and crackling. Bad cap?

[Diamondj421]

As the title suggests, I have a pair of Adam A7X’s that I want to sell but after moving, I plugged them in and one was making a terrible buzzing/crackling sound with and without anything plugged into it. It would normally settle down once the monitor was powered on for about 30 seconds or so but it would eventually come back. I’ve tried multiple outlets, locations, power conditioners, etc but nothing made a difference.

I opened it up today and noticed that the top of one of the larger capacitors on the board appears to be bulging a bit. I’m not sure if it’s bulging enough to assume it’s blown though. I’ll attach some pics and any input you guys have would be incredibly helpful!

Thanks!
Jeff

 

[Bobby Baird]

Looks Like the black goop of death that's slathered all over krk circuit boards. That glue actually becomes conductive causing issues like that blown power rail filter cap. Yes, I would replace that capacitor and clean up that glue away from through holes. I had the same problem with my krk's buzzing and crackling. I replaced all power filter caps with some nice Würth caps . Quiet as a mouse now for several years now.

 

[Wado225]

As the title suggests, I have a pair of Adam A7X’s that I want to sell but after moving, I plugged them in and one was making a terrible buzzing/crackling sound with and without anything plugged into it. It would normally settle down once the monitor was powered on for about 30 seconds or so but it would eventually come back. I’ve tried multiple outlets, locations, power conditioners, etc but nothing made a difference.

I opened it up today and noticed that the top of one of the larger capacitors on the board appears to be bulging a bit. I’m not sure if it’s bulging enough to assume it’s blown though. I’ll attach some pics and any input you guys have would be incredibly helpful!

Thanks!
Jeff

Did you ever figure a solution for this? Seems I'm having the same issue with my A7X

 

[Diamondj421]

I never did get it figured out. I replaced the caps, turned it on and SNAP! CRACKLE! POP! I didn’t have a chance to open it back up to see exactly what blew (nor did I want to at that point). I had bought a new pair of Kali Audio IN8s so without needing the A7Xs, the project was put on the back burner. I’ve been meaning to get around to it again though so I can unload them. I’ll keep you posted when I get around to it. Please do the same!

 

[Khron]

Where are you based?

 

[sortedaudio]

I have had this problem with several KRK Rokit monitors. As Bobby Baird has said cleaning off the black compound and replacing the caps does the trick.

 

[verbos]

I think you will find that all of the garbage caps that they use in those need to be replaced. I have now had 3 Adam monitors have this happen to them and in all cases replacing all the electrolytics and scraping out all that black glue solved the problem. They use the cheapest caps on Earth and they operate in a very hot environment. Also, maybe that glue is doing something bad.....see above. Buy good quality caps that are rated for much higher temperature.

 

[nashkato]

had that issue on a krk 10“ subwoofer.
in my case a bad ceramic cap in the preamp section was the problem.

 

[Diamondj421]

I’ve replaced the 6 larger 2200uf 35v capacitors then noticed two other capacitors (470uf 25v) that were bulging so replaced them as well but the problem persists. I bought replacements for every electrolytic capacitor on the PCB so I guess I’m just going to go through and replace all of them.

 

[kags]

I've had bad experiences trying to cure problems on these type amps - the glue on the components becomes conductive and then weird things happen. I've tried to repair Tannoy and KRK subs and always wind up simply replacing the amp with a new plate amp. The repair would be worth more time than the cost of a plate amp from Parts-express or somewhere else... I know this is a DIY forum, but this repair may not be worth the time. definitely keep us posted...

 

[NoisyIndividual]

OK, but then once you have supplied the customer with a brand new plate amp, surely you have to then offer a guarantee on the part?

What happens if this plate amp blows up after 3 months?

 

[kags]

I think the current generation of plate amps is much more reliable than the ones from the early 2000s. It’s frustrating that there isn’t a standard plate dimension. I’ve even simply covered the hole in a sub box with msg and used a plate amp in a separate enclosure. Always some workaround needed. Still usually quicker and less labor that repairing a “gluey” old board.

 

[Matt Syson]

It is interesting watching the internet speculation about various problems (crackle buzz etc) when so many simply 'parrot' a bunch of myths without understanding the failure modes of various components and the nopise/intermittencies/whatever they hmay or may not make. From this thread alone it seems that the partially conductive 'glue' that is often used (missapplied) is a significant issue but it is just one of a range of possible explanations.

 

[jp8]

Judging by the photos, at least one of the elcaps looks like it's bulging. But that could be an optical illusion. Anyway, like others already pointed out, it's recommended to recap the whole thing. I assume the caps pictured are the output reservoir caps of the switching power supply. They should be replaced by name brand types, such as the already proposed Würth. Or Nichicon, Rubycon or Panasonic to name a few. Look specifically for low ESR, 105C types with the highest ripple current rating you can get. If you use cheap, general purpose 85C types, you're back in trouble in no time. You can use the Mouser or Digikey selection filters to find the right types.

Good luck repairing the speakers!

Cheers, Jan

 

[NoisyIndividual]

I've just had a quick look in my repairs database, and out of around 70 KRK speaker repairs, around half of those were the conductive glue problem.
A smaller sample of around 24 Adam repairs shows 2 Electrolytic Capacitor replacements, and 3 conductive glue problems.

(Many of these came in as pairs, so more individual speakers than quoted)

 

[ElSmurf]

Might not be the caps. Is the crackling coming from both the LF and HF driver? Did you try swapping out boards to pinpoint the problem?

I had a similar sounding problem with one of my Yamaha HS5s, ended up being a SMD ferrite bead (I thinks) right before the power amp IC that was detaching from its solder base.

 

[RoadrunnerOZ]

That cap in the photo is definitely bulging. It’s a common problem in powered speakers due to heat and possibly also constant vibration of the internal elements of the electrolytics?? - for some reason in some speakers it’s always the same cap in the same location - not sure why. Quite often in linear power supplied units it’s the rectifier diodes or a failing voltage regulator that triggers the problem. In the switch mode supplied models the problems are wide and varied. The glue used in some brands to stop capacitors ripping the boards apart from vibration can become hygroscopic with heat and age and it sucks moisture in as the units cool - when you turn them on again all bets are off depending on where it’s slathered. I always check for HF on the power rails as well - problems in audio power amp circuits can pass back to the supply, you fix the supply but there’s still an underlying problem.

 

[jp8]

I've just had a quick look in my repairs database, and out of around 70 KRK speaker repairs, around half of those were the conductive glue problem.
A smaller sample of around 24 Adam repairs shows 2 Electrolytic Capacitor replacements, and 3 conductive glue problems.

(Many of these came in as pairs, so more individual speakers than quoted)

Aha, here we have someone with a lot of first-hand experience with repairing these speakers. Do you happen to know which failures recorded in your database could be related to the phenomena the OP described? The crackling sounds could still be caused by something other than the caps of course and if it's a common problem, I guess you will have some records of that. But I still maintain that in the case of bulging capacitors, it's best to replace them all. Call it preemptive maintenance, if you like.

Jan

 

[RoadrunnerOZ]

The other thing I’ve come across that causes problems in speaker amps are NTC’s in series with the mains for soft start and spike suppression caps across the mains switch - I’ve had them with the sides blown out - maybe because they use 250V caps on a 230/240V system.

 

[NoisyIndividual]

But I still maintain that in the case of bulging capacitors, it's best to replace them all. Call it preemptive maintenance, if you like.

Jan

Well its actually quite common to come across equipment that very often has the same component fail, as Roadrunner said earlier.
It is known that these power supply caps bulge in these speakers, and it is also known they suffer from the conductive glue problem. This does NOT mean that all the other electrolytics in the unit are or are likely to be in a similar state as these 4.
It seems companies make poor choices, rather too often, and cheap out with things like a particular value capacitor at a particular voltage. Or maybe they get ripped off/misled by the cap manufacturer, or they produce a sub standard batch, or they get damaged during assembly. Who knows.

By all means go and replace all the electrolytics if the speaker is yours and you have the time and money to do it, this is not always an option if someone is paying you by the hour, and replacing everything, just in case, then makes the repair uneconomic.

I will check the other caps with an ESR meter, just to check there are no other values that also are failing. Usually there aren't.
Most (not all) will test in circuit.