Hi, it's repair time. Check it out! We've got a Krk Systems Ro Kit 6, which is a 6 inch powered studio monitor and by many accounts this is actually quite a recently regarded studio monitor. And of course, yes, Q or the fanboys about our that's Crap and everything else made in China but designed and engineered in the United States of America and Quality Assurance inspected. It's got to be good.

So yes, it is a reasonably expensive studio monitor I've only got the one of them and apparently it's faulty. It makes a buzzing sound when you plug it in cover before powering on loud, so I'm yeah, I'll take that off and maybe put a bit of thicker cardboard on there or something. and ooh, fingers crossed. If you want to know what our studio monitors I use I use the Alesis 520 USB ones I prefer the USB I Don't necessarily like these ones from a convenience point of view because I Love having the volume control actually on the speaker's themselves and on the front and the headphone jack on the front as well cuz I'm always plug it in my headphones to, you know, record the amp hour, or record other things or listen and stuff like that.

It's just very convenient to have it on the front of the USB speakers and the volume control just there. I Can tweak it to my heart's content. so I don't like these ones that have the volume control on the back of this one's got yeah it's got volume and all are nice indents on that and it's got a high frequency art level adjust as well. That's for the tweeter plus 1 DB and minus 2.

So I'll put a minus 2 because it's supposed to be loud and unbalanced the inputs. This is not a USB one. Anyway, let's turn it on, see what it sounds like? Ok I Know it's probably not good to do this, but guess what? we could damage the tweeter or the tweeter could already be damaged. I don't know.

but anyway, we have to look at the symptoms. so plug it in. Here we go. Oh yeah, Wow I Can feel that vibrate that poor little tweeter Wow It must be getting the full like like square like the eye.

The amplifier must be oscillating and put in a full the full rail voltage square wave into that thing. That's all I can think of that is horrid. So anyway, let's take it apart. We've got four screws on the front.

Looks like we can pull out the drivers, but I suspect we're gonna have to take the screws out the back to get the board out cuz that's what we're really interested in. So I'll start with the back one around here. let's go up: I Expect this thing to I Think this is is this a boy amplified one that actually has a separate amplifier of the wolf ax and the tweeter? I Think so in this case, the tweeters oscillating so it's almost certainly a boy amplified as they call it with the two amplifiers. and I expect this to have one of those like integrated, you know, off-the-shelf power.

The driver chips probably like a single inline package one. they're very common and I just had a look online and I didn't want to I get any spoilers for you know if this is a common fault with these things, but I was looking for the schematic couldn't find it on first search. So even if the schematics not available should still be relatively easy to work and repair and troubleshoot something like this. Because as I said, it's probably going to use a like one of those off-the-shelf are amplifier chip saying she'll be able to get the data sheet for that, it'll have the app note.

It'll probably follow the app note very quickly. The piece of B in there might even be if you're lucky. might even be single-sided which makes it easy to trace and things like that because they do try and build this down to a price point. so you know, why use a double sniff angled double-sided piece of e if you don't have to.

But this one's probably double-sided. but anyway, should be relatively easy to track this one down. Anyway, let's go. and as is common with these things, just self tappers into particle board / MDF if you're lucky, these would be solid if on the outside but could have something else on the holding the screws in.

Wow All that is one heavy ass back panel. Everything's going to be mounted on there. It's probably got the power transformer on here, so let's go in there. Yep, that's that's not MDF is it? Anyway, we're in like Flynn Check it out! Ah, nice shielding on the transformer down there.

Wow, They're done well and actually this looks rather nice. Look at all the heat shrink tubing on the back of the mains wiring here. That's absolutely brilliant. Got some filter caps in there.

it's all cable. It's all really bundled and cable tied very nicely. Um, we've got the connector here gunked it down so it doesn't vibrate loose. Once again, the main power wiring over there is also gunk down so it doesn't come loose.

Oh, they got some gunk on one of the supply caps there. Yeah, they're just gunked up everything. No, the junk gunked-up the output of the transformer there. Somebody had fun.

Anyway, this is a very typical arrangement for something like this. We've got our preamp board of course and our input. like a preamp and filtering and stuff like that like there could be something wrong with that and it could be feeding the signal into the driver. but I like I think it's more likely than not as something wrong with the driver and that puppy's isolated.

I Don't expect to find it on the preamp board anyway. we could actually test that I Guess by just can we could we just disconnect the input board and see if it still does it anyway. and I just I Just love all the rubber they've put inside this thing. And look at this.

this is the RCA connector input and it's in like a block. It's in like a compliant mount block. Wow, that's like that's why have they done that? I mean I Can't see why you'd need to vibration isolate the the RCA Oh no, no, there we go. No, it's not.

no hang on what? Okay node, it's screwed in all right that doesn't feel compliant. Let there's no need to do that. That's just really strange. anyway.

Um, yeah, good attention to detail on this thing. it would want to be. It's not a cheap unit. Wow Check out the rubber mount on that transformer.

Beautiful. And of course, inside the box, we've got our standard filler material that's just all whacked around there. That's pretty common. KRK Drivers I Don't know where they actually you know, get them from if they make them themselves or whatnot.

or they just get them from some supplier. Oh, of course you know there's nothing wrong with where you get them from. as long as you you know, as long as the quality is are controllable and the performance is there, you measure in, characterized, aimed, a design, your enclosure, and everything else around your driver. So anyway, now poor little abused tweeters up the top there.

But it's interesting that the Spade likes, but good that we can. Just no, no. Actually, they've gone up to the tweener. That's interesting somebody.

I don't think that's factory original. that's going up to the tweeter. There's no reason. Look, the woofer is soldered directly on the board.

Maybe that's a bit. how are you doing? Not sure, but okay. it is what it is that goes off to the woofer. but or the full range dry of mid-range driver or low range driver or whatever you want to call it.

but the tweeter has Spade connectors. Somebody's that it go at least disconnecting it. And for those preamp aficionados, there you go. J RC Japan radio A Corp There are you know, really common as mud in these types of stuff.

They make reasonable op amps, the audio stuff, and op amps, and what nightime even the single inline package down there as a JSC They still couldn't get all the couldn't get it all routed on there and they've had to put a few little jumper links on there. Oh, first rule of troubleshooting before thou shalt test voltages because we're not up to that point yet is a visual check. So I can't see anything on this preamp board. But as I expect I wouldn't suspect it, it's more likely that there's something wrong.

power app so there's nothing visually wrong on there at all. Basically, what you'd be looking for is burnt out resistors you know, or other components bulging electrolytic guy caps of course. But these tiny ones? no, that's nothing. They've just put some black gunk on that.

so that's all hunky-dory All right. Thankfully, the power amp module just screws off the back panel there. Now we can have a look down in here and once again, we're going to be searching for any visual signs. Of course you check the the caps over here.

Yiquan. Come on K Okay, you know you con don't think I've heard of them anyway. 105 degrees C rated. Come on.

put some you know really top quality brand caps in there. Jrc again. but once again I See is gunk everywhere. Check it out like they've put it all around the shop.

Yeah, those single inline package power amps. as I said, they're not using discrete in there. But look at this. This is our tweeter based on the wiring okay and the fact that the tweeter will be less power than the woofer by amplified.

so separate amplifiers for each. So this was at two, four, six, eight pin. no seven pin package down in there would be the tweeter amplifier. But look so this is the wiring and look at all the black gunk down in there.

They look there's a poor little resistor or something under there. I'm just wondering if this black Young has like become or is what wouldn't be when you first put it in. That would be dumb. but David's become conductive, contaminated or something like that cuz it's all down in there.

Look at it. I really don't like that and all down there as well. Well look at that. I mean like yeah, that's horrible stuff I don't like it and sure enough, look at this.

If I probes some of this gunk I'm not actually touching a component there. it's like a MIG like what that like that's just like that's ridiculous. Why would you have anything in there that starts to go conductive with age or or contamination, moisture absorption, or whatever the hell is going on with this stuff? Check out this insanity if I measure on the top of these electrolytic caps here which have been gummed together right? Look at that. I mean this is insanity like look I'm not even touching the top of there the top of the can there and it's conductive like yeah it's high, but it like that can create feedback, pass or whatever it is like.

that's just ridiculous. Yeah, yeah, there's a close-up of this gunk conductive gunk trademark. I Do like their attention to detail on this board here. look at this.

They got a rubber baby buggy bumper on there. Nice. The vibration isolation obviously for those bottom boarder fishy and oh noes, there you go. They got some tin plate on there to help with the current handling on the requisite traces.

but do you know generally there's not too much going too far on here. The speaker's basically come straight out. All right. let's turn this puppy back on.

Hook the scope up to the output. I've disconnected one lead of the tweeter, so let's put it on. We're on what? 50 volts per division or something like that? Let's have a go. Hey there we go.

Just as I thought big-ass square wave because that's what it sounded like. There you go at what frequency? Interesting to note that it takes a few seconds to come on. I did see a relay on that board, so it's like got a pair under thump protection or whatever it is it's called. But yeah, there is your problem.

61.7 Hertz at Forty volts peak-to-peak Yeah, that'll blow the snot out of your driver. so our amplifier is, well, certainly amplify amplifying too much. So what I'm gonna do is just like fer before: I attack this getting things like that, like try and reverse engineer it and you know, figure out what chip it's using all that sort of stuff. I've gotta try and just clean up that conductive gunk I've found and like you know, because look, it's right on the output.

it's right on the dam output. Why? I go into the pot the positive output of the driver for the tweeter and it's oscillating. So I'm gonna get try and get in there and somehow I'd hopefully it dissolves off with you know, some sort of PCB cleaner or something like that otherwise might have to do some scraping. I like I Found an issue there I'm gonna fix it now.

This is interesting. If we pair it up without the preamp connected, we don't get the oscillation so, but that doesn't mean that the source of the oscillation is coming from the preamp board and it's been fed in there. It could be the fact that you know it's not switching the relay in there and it's not turning it on I don't know, but there is a DC offset on that output. Certainly.

hmm. Anyway, this is interesting. if we turn it off, listen, goes down, Down Down. Maybe you can hear it.

hang on and I was like a little farting noise coming from there as you I switched it off and yep, I plug it back in and it's back. and I've cut out all the black gunk off between all the tops of the capacitors are on there, just in case. There's like three different areas where the black gunk was shorting out the tops of those cans. It shouldn't make a difference.

they may be at all the same potential, but maybe they're not. Maybe there are some AC coupling caps or something, but that didn't make a difference. I Found that this black gun it does tend to actually flake off, so maybe I could. Yeah, there we go.

Maybe I can try and get it out. Get it out that way. Bloody heat sink compound. so there you go that actually scraped off.

Okay I'm gonna still give it a clean with a you know a PCB cleaner flux remover thing just to brighten it up a bit. But anyway I've gotten rid of the crap that was around there and really that was cause in that would have been causing leakage between the speaker output. Whatever this little resistor here's here and also this link in here and that link also it maybe seems to have corroded a bit. Hopefully can see that down in there.

doesn't look great does it? Hmm okay let's pair it up against worth a shot and got a DCI hello do we look at this? I I'm pretty sure. yeah I'm still properly connected. Yep, yes we fixed it. Wow.

I Didn't realize that the odds wouldn't have been great that they would have been here, but I thought you know that was definitely conductive problem. but look, we're still got some crap on there. mm-hmm where are these little bursts coming from? Wow, that's interesting. Whoa, look at that.

Okay, but at least our 40 volts peak-to-peak is gone. Awesome. No hang on. we've repowered and it's doing it again.

but it's not square. Look at that and it's frequency. I'm sure was changing. What was that? 61 Hertz before 350 Hertz Now and it's changing.

You can see the period about change in Wow hey this knob on the siglent I swear for a second there didn't respond to my range change I swear I did the indent I can't reproduce that? Hmm. Anyway, that's different Wow as that gunk was doing something and it's still doing something well, presumably and I turn it on again and we're getting something different again. What? Wow, this thing's all over the shop. hey, is that some like 50 Hertz Hamas Oh no.

Saw a little spike in there. It said like 50 Hertz hum any microphonic s-- yeah, there we go. she's a hundred Hertz So that's your mains. That's your full wave rectified mains.

Doing funny business down there. And of course there is a don't have my isolated poker, but there's a full wave bridge rectifier down in there and that's what we're seeing manifest itself with some high frequency stuff. Wow Hang on. Yeah, this is fun.

Wow got some sort of microphone X I'm tapping the board there I haven't actually cleaned up the gunk here on the board around these low ESI caps here either. So I'm gonna go in there. pick all that out as well. clean it all up.

Wow Check out all the gunk in here on the bottom of these resistors here. bottom of a couple of diodes down there. across this link. right near this is the negative terminal for the tweeter and look, it's almost as if like it's bubbled.

Oh wow, it's that. That's weird. I'm looking through the camcorder screen. It's hard to know what I'm looking at here, but jeez, that's it's like it's almost bubbled up.

What the hell? Anyway, it is conductive and what does that conductive caused current to flow through and it probably changes its resistance. Well, it's down on there. Is that that's not from my Sprite? Is that gunk? Wow What it's almost liquid is it is that from my cleaning? it might have I cleaned the other edge of the board I didn't clean around here, but it's bubbled up the hell is this stuff? Anyway, it's definitely gonna be some. Well, one of the causes for the issues we're seeing here and of course something.

Wow Wow The hell is this stuff unbelievable. Good news is it flakes off even after I put the solvent on it. it's still hard and it just sort of comes off in in chips. Oh well.

I actually had to. D So love that cap because it was a pain in the butt to get into it and look at. there's the black gunk there. It is there.

and no, it's not leaked out of the capacitor. They've deliberately added this to try and reduce the vibration on the parts and they've come a gutter. It's backfired on them and it's become conductive. Unbelievable.

actually. let me get the meter on that again. there's a piece of it down there that I mean it's high, right? but still. that is ludicrous On the side of the cap.

let's have a look. look I mean you know it's like it's very high, but it's leakage and that could certainly be voltage are dependent as well. And particularly when you're talking about amplifiers, you know nothing's working down it. People in little 3.3 volts, everything's up at like you know, 30 40 volts kind of thing.

and this is just unbelievable. Well done Kayak! I Put in conductive gunk on your boards. Of course it probably wasn't conductive when they put it in, but it's become conductive with a judge say and a problem. Certainly your money's worth in the gunk.

and this is the negative lead of the main driver. It's just unbelievable. And there's the positive lead. Houston.

We have a problem I did not do so. Do that poor innocent resistor there. It's just did it break off or something? Or is it it doesn't look charred or anything. but I think it's covered in gunk? How can you tell? I didn't touch it I Swear that poor innocent little green cap is just swimming in the stuff.

Surely this has to be an Owen problem with these, doesn't it? I mean how many speakers out there would be affected by this? I Can't believe this is the only one Black don't plague I reckon that is corroded I reckon the black gunk has actually corroded done something to that poor resistor. looks to be 2 point 2 K I've measured it, it's still there I'm within its 5% but yeah I reckon that didn't like it, just fell out, just fell out of the board. Unbelievable. Okay, I should have cleaned it up in most areas there.

I've replaced their resistor I put the capacitor back. In fact, their resistor I didn't have a 2k two in that are high what is? So put just mound a couple on the back as well. I've got a 6k, 8, 4, 3, 6, K eights in parallel. She'll be right.

No worries. So let's turn it on and what do we got? Yeah, that's different yet again. What is that? There's some hundred Hertz hum on there once again with the if you will little excursion. Interesting.

Okay, so I've got a speaker reconnected now. let's give it another go. Yeah, we can still see a DC I'll sit there with a bit a hundred Hertz but that's feeding a signal. see what happens for those playing along at home.

The tweeter driver is a TD a 205 2 and the woofer driver is a TD a 7286. Is it or something like that? I can't see it's got some gunk on it. No, that's not a burn mark and we know Winner chicken dinner. but I still don't like the waveform they're still going to eat DC offset they're at.

Well, it's only 100 millivolts, but not sure if you can hear that I've got a 3.3 generating a 3.3 kilohertz signal into it just from my phone because well, I you just. it's easy and be just to avoid any ground issues with I like if we use the signal journal or something like that. So and the attenuator works on the back here, you can see it boost zero dB You can see it drop by one DB 3 DB and then boost it by 1 DB So that seems to work. cool.

Hmm. and it doesn't look very sinusoidal II does it and it's just like really harsh. Like there's some sort of other. Is that like it? maybe? Is there have the hundred Hertz hum superimposed on there? Like coming.

maybe coming from the woofer? No, because we didn't hear the woofer before. If I disconnect that turned off. There we go. Hmm.

Well, the woofer is certainly woofer in, that's for sure. One point five K 2 K Yeah, you can hear that combined. Not sure if you can hear that, it's like some sort of combined hum in there, but hey, we are getting in a good slow wave. now.

What was what's gone? Oh yeah, it's pretty harsh. There's something else going on. Wow Yeah, check it out. as we go higher in frequency, we're we're good.

Decent sinusoidal now. but after below about four kilohertz starts to distort a lot. Then of course it gets so low that say that's going into the that's going to the tweeter. Something's wrong there.

That's a one point one Kilohertz. Yeah, it's still a bit sick, but basically the amplifiers working both of them. Now if I actually disconnect the tweeter, the woofer actually sounds pretty good over the frequency range. so that's okay.

So maybe we. well, of course because you saw how it was like physically shaking I could feel the vibe huge excursions of the cone on that tweeter and they're not designed to do that when I was plying that forty volts our Peter peak square wave across it. and we're probably cost some mechanical damage, so they could certainly it caused the distortion I was hearing. plus maybe it feeds back because I was measuring directly across the coil there.

So maybe that was affecting the drive that was seen on the arm scope. So anyway, let's have a look at the drive signal without the tweeter and that is as clean as a whistle. Without the tweeter on there, you might still be able to hear it, but that's some of the woofer actually doing that. So I think now.

waveform distortion is caused by the physical deformity in the tweeter. That's the Bobby Dazzler There we go. Yeah, that is. That is fine.

You can see the amplitude chop as the frequency goes down. That is fine. So well. Well, I think our air board is working just fine, but our tweeter, it's routed.

and yep, I've got the tweeter connected. There's a very distinctive lack of high frequency content there. My voice is usually very high frequency Wow So let's get this front panel off, shall we? and have a look at that straighter. Oh, there's the poor little puppy.

Ah, poor abused little thing. Okay, okay driver, there you go for ohm tweeter. But like seriously, I'm sure it's completely naked because when I had my hand on there when I first powered that up I could like feel the excursions hitting me. It was just insane from a tweeter.

Wow actually it's completely open, don't All right? Just as a temporary job I've budged in this Soni Driver: it's a 12 ohm as opposed to a 4 ohm bit near whatever. Hopefully we'll get something out of it. This is like a mid-range driver, so anyway, look at some sort of response at least hopefully and see if it sounds better. It does sound a bit benefit anyway.

I do have a great anyway a buzzed out the actually. let's plug in the companion tweeter by way of a little capacitor filter there. Um, it's just a little piezo type of. these speakers came from a Sony crappy Sony 3-way speaker.

live get and let's give that a ball. There we go, that sounds decent thing. A rather Radian I carded I believe it's you know, hugely powerful, but good enough around this sort of all in one purpose. And there's our webcam attachment there that's going up there.

so that's the that's the NSA Edition So until I get the the real tweeter in there to, you know, check us performance I can like, like sweep it and analyze it and do all sorts of our other stuff, but it basically sounds quite reasonable with a completely crap non matched a mid-range and tweeter in there, but the amplifiers seem to be doing their job no worries whatsoever. so I guess kind sorta thumbs up to the amplifier for not crap in itself, but on the other hand, the physical construction of it while the rest of it was good, this black gunk is absolutely ridiculous. and sure enough, I had a look and like apparently this is a thing with them I Don't know if it's in the newer generation row kit speakers, but certainly older. Jedi Believe this is a Gen 1 speaker.

so yeah, it's got the original black gunk of death I guess and it's just turned to this hard conductive crap which was causing the amplifier to actually oscillate. Unbelievable. and it looks like it caused a resistor to I just like corrode away one of the leads and it's just basically dropped out. but like, apart from that I just put the resistor back in and Bob's your uncle.

It seems to be at least going again, so I'm gonna until I can get like a replacement tweeter I don't know if I'll even bother really with the crusty state of the board in this thing and the fact that I've only got one so have to get another one a gen one and then they like other even matched. Are they a match? Design them as a match pair or whatever? I don't know. It might be useful for something. I'll just use it as a lab powered speaker or something like that.

here for the bench might do it. So yeah, I can get a replacement tweeter for this for about thirty bucks or something like that. maybe. Yeah, it's a bit pricey, so if one goes on special, I might pick one up and get it back into fully operational condition.

but I'm gonna call that one basically repaired for now until I can get one if anyone's got a spare one, they want to send another male baby by all means otherwise. Oh, I get one on eBay if one comes up cheap, so wonder if they ever actually recalled these things or not. Or you know, like, because that's a huge problem in how long did it take for it to show up? Typically, if you've had this Kok black gunk of Death problem, then leave it in. The comments down below let us know how old your speakers were before he started to shut themselves.

We sure took quite a few years for it to actually you know, start happening. and I've been reading a little bit. people who like reported other symptoms I didn't see anyone who had the big 40 volt excursions that I'll see and that killed my poor little tweeter. um actually I don't know what happened to it cuz it was actually it was kind of working but when I took it all apart then it was like it just died.

so I don't know like their physical just doing that and something inside just went kaput. I don't know. Anyway, she's open as so huge thumbs down to Krk for that one that was just an epic fail. Has it kind of ruined me for karaoke speakers? I don't know I don't even think they make one with like a volume control and headphones jack on the front do they? That's what I need for my studio monitoring anyway.

mm-hmm Anyway, they certainly come a guts are on that one didn't they? But that was like an interesting repair. You know it wasn't really a component electrical were a component failure, it was something that was put on the PCB to try and stop as you do inside these things. It was good design practice. I Like a lot of the design practice inside this thing, it's a quite well engineered in that respect.

but the black gunk that they put in there silastic or whatever it is. If you know the exact type of material they were used in this that went bad, please leave it in the comments down below. Um, but they you know we're doing that as a good thing. you know, stopping the capacitors flapping around in the breeze, stopping the cables and connectors and like other stuff.

but and and the wires on the on the board providing a bit of a strain relief coming out of the PCB and stuff like that so that we're doing the right stuff. it just it can pack and beat them on the ass. Murphy Anyway, hoping like that if you did, please give it a big thumbs up. And as always discussed down below and yeah, go on Speaker fanboys K Okay, oh crap, Roki to crap we're oka degrade I Love my Road kids, oh yeah I love my Alesis ones.

the 520 USBs do me just fine for a compact video editing monitor speaker. Anyway, go for it. audio. There's just no end to the fly.

mean catch you next time.