please read "Same." not "Same?" in 1st §

ot, but isn't krk another gibson brand? get anderton to give them a kick...

Nicolas59
NOW AN UPDATE : I have not done yet these steps, but a new situation has arisen. First, let's name my monitors: Monitor A is the faulty, Monitor B is the good one. Since I swaped the tweeters last week, I have been listening to some music on my monitor B alone, now equipped with the tweeter from Monitor A. And this was OK.... well it WAS because it IS not anymore: for the last 2 days, I have some new annoying popping or crackling noises now in Monitor B.

 
How's Monitor A doing now ?  Is is now playing ok ?  If so, it certainly points to the tweeter.
 

Shall I conclude that the original A tweeter is responsible for "contaminating" the electronic circuits that feed it !?! It looks as if there is a sort of interaction between one and the other... it looks as if my tweeter is a Killer ! killing the electronic, would it be possible ?

 
If monitor A is indeed OK, then just moving the tweeter around may have jolted its voice coil enough to play properly for while.
 

Hi everyone
I am a pro keyboard player living in Cape Town South Africa and recently decided to create my own home studio. Nothing special, but included in my setup I use a Focusrite 2I2, Kurzweil Artis and a pair of stunning KRK Rokit 6 FR 2nd generation monitors. They are around 4 years old so no warranty unfortunately.
After an hour or so of use, the one monitor begins making what I can only describe as a distorted pulsating sound which seems to speed up and suddenly the woofer produces no sound whatsoever. The tweeter continues to work fine. The second monitor has no problems at all. After unplugging and unpowering both monitors for a few hours, I then switch both on and the they both work flawlessly...until that weird distorted pulse returns after an hour or so and the woofer again stops functioning. 
After replacing ALL cables including audio and power, the problem still persisted. So, I took the monitor to the only qualified technician at a local music store (the agents for KRK) in Cape Town who, after running it for a few days, reported that there were " no problems found". Imagine my surprise! So I collected the monitor, plugged it all in and sat back to enjoy my newly serviced Rokit 6.
Alas! My joy was short lived as at around an hour later.........well.....same thing. 
Took it back to the technician who kept it for 2 weeks and replaced various amplifier parts and gave it the "all clear". 
So now I'm sitting here at my home studio experiencing the same problem once again. I have searched for so long to try and find out whats causing this and have found this very informative site.
Is there anyone out there who can provide any solution to my apparently unsolvable problem? As you can imagine....I would be most grateful. Thanks
 

garthV...I have searched for so long to try and find out whats causing this and have found this very informative site.

Hi GarthV!  Welcome to the forums!  And I'm glad you found my thread informative!  As far as I know, it's the only thread/forum out there that discusses and finds a solution to the "garbage goo" that KRK slathered all over their circuit boards.
 
As far as the repairs that already took place, I would be curious to know what parts were replaced if any.  Perhaps a look inside can reveal a few answers.  Be careful of large capacitors that can retain a charge.
 
Is the "distorted" pulse periodic and/or have a definite "waveform" to it, or is it sporadic/random?  South Africa, I believe, is 50Hz at 240VAC.  Is this correct?  Does the "distorted pulse" sound like it could be 50Hz or 100Hz in tone?
 
Try plugging the speakers into a different power outlet/receptacle.  Still an issue?  Does the problem persist if only the power AC cable is plugged in, i.e. leaving the audio connection unplugged?
 
The "goo" that KRK used on the circuit boards does more harm than good.  Seriously, the stuff is bad news.  I would suspect first this crap to be the issue on the power supply board.

Thanks for the quick and helpful response. Much appreciated.
I too am curious as what was replaced in the monitor. That info will become known soon as I am about to request that info from the tech. I will however open it up and have a look to see what my completely untrained eye notices. Don't worry, I'll try not to touch anything. I have a healthy fear of being shocked.
Is there a safe method of "disarming" built up static charge in the amp once I've powered down?
 
It definitely is always the same noise and only occurs 30 seconds before the woofer shuts down.  I never run my monitors at high volume and usually do not position the volume pots at more than 30% which eliminates some possible causes I guess. Also when I hold my palm against the rear panels (when this occurs) they both have a similar slightly warm feel to the touch. This I'm guessing is normal.
 
Yes we are 50Hz at 240VAC.  I am yet to confirm whether the problem exists with only AC power leads attached. That will be my next test. Thanks for that bit of info. Regarding the power supply, the original AC cable was a single plug to the wall socket with power lead going to the one monitor and being sent to the other via the same cable.i.e from the wall, to the monitor "A" kettle power input,and a feed to the second monitor "B". I think its called a Y cable. Sorry if I'm not making sense. So ,thinking that that could be the problem,I bought 2 new separate power cables ,one for each but the problem continues. So I've eliminated that one. As I type, I am hoping to be able to record with my mobile phone, the moment of breakdown so I can send you an audio clip of the offending noise but nothing yet. 
As for the noise itself, what happens is the following....music will be playing normally then what I hear is loud distortion over the music, seemingly in time with the music beat as if it was digital. That continues for around 30 seconds then the music disappears from the woofer to be replaced by a fast mid ranged "blip" which quickly slows down over 5 or 10 seconds.Then nothing. By the way, my mistake was to say that it speeds up...just the opposite. The blip can be described as.... well.....it reminds me of the 1980s arcade game "Asteroids". LOL!! I know I sound like a moron but I cant think of any other similar sound....except that it's maybe something I may have been able to create with my old Sequencial Circuits Prophet 5 back in the day.Does that help? 
 
Playing my Artis directly into Monitor makes no difference so its not the Focusrite. Also tried Ipad, Iphone and  PC direct in and still the same problem. Bought top end jack to jack cables...no change.
So, my next few steps will be.... a) Call the tech to find out what he replaced 
                                               b) Open the cabinet and have a look around
                                               c) Try running it without audio in leads
 
I have read with interest your article on the "goo" and I think you're spot on. Not that I can tell but you sound very knowledgeable on this topic. Your input and help has given me some hope that all may not be lost. Thanks. I will post more data as I get more answers.
 
 

If the monitors work when cold and then fail after a period of time then it sounds like a thermal problem. You should be able to see some physical signs like bulging caps that are leaking goo, burned resistors and that type of thing. In this case it could be a component from the crossover. Most electronics are made with the cheapest parts they can get away with. Resistors near heat sources have to be able to stay at their design values when heated. Some times they get the wrong type of resistor on a board and when it heats up, the value drifts by a large amount and destabilizes the circuit.
 
I have these monitors and keep waiting for mine to die so I have an excuse to take them apart. If you have tech skills and a multi-meter you should be able to check component values before and after a failure. Another angle would be to use a dedicated cold spray or even compressed air in a can, to spray cool the board after a failure and see if it comes back.
 
Happy hunting.

Hi 2:43AM Thank you for your post much helpful
I have the Rokit 5's same issue cleaning them up solved much of the crackling but not all so I ordered the components you did and noticed the 5's use the Panasonic 2200µF 50v capacitors not the 3300µF ones I ordered from digikey is it ok to go higher or should I reorder the 2200's?
Thanks
Mike

mriebese
Hi 2:43AM Thank you for your post much helpful
I have the Rokit 5's same issue cleaning them up solved much of the crackling but not all so I ordered the components you did and noticed the 5's use the Panasonic 2200µF 50v capacitors not the 3300µF ones I ordered from digikey is it ok to go higher or should I reorder the 2200's?
Thanks
Mike

Since the "BIG" caps are on the main power rails and ground, I think you should be okay with the larger size.  It shouldn't affect the operation of the amplifier circuit, nor are they in the audio-signal path.
 
Take a look around the amplifier board, and compare it to my first few pictures.  Does the board mainly look the same?  Can you see and tell me the part numbers of the two amplifier IC's stuck to the heatsink?  How about the transformer?  Can you report the output voltage on that too?

2:43AM
 
 
Since the "BIG" caps are on the main power rails and ground, I think you should be okay with the larger size.  It shouldn't affect the operation of the amplifier circuit, nor are they in the audio-signal path.
 
Take a look around the amplifier board, and compare it to my first few pictures.  Does the board mainly look the same?  Can you see and tell me the part numbers of the two amplifier IC's stuck to the heatsink?  How about the transformer?  Can you report the output voltage on that too?

Thanks for the info the circuit board looks identical I will measure the PS output tonight and get the P.N.'s of the IC's but heres a pic of my board in the meantime
 www. dropbox. com/s/wg6alqo0ou0m0df/IMG_3987.jpg?dl=0

 
The IC PN is TDA 20528800MV6 on the second line letters and numbers SGP  834
The PS is outputting 18.6 v AC on the red wire and 17.3 on Yellow even though the labeled specs are 17.4 & 15.3 respectively
PS p.n. is KRK ROKIT5 (RP5) TT066030552B built 02 09 (Is the PS a problem being too high?)
Even though I already ordered the 2200 capacitors from DigiKey as it was  less $ than the 3300's I'm eager to try and get them going this weekend
 
Thanks
Mike