Great presentation. You should send it to Gibson.
 
If you are going to replace resistors I'd recommend you go with metal film. They are extremely quiet and don't seem to be bothered by thermal drift. I've not opened mine yet because they still work. This looks like a major design flaw at KRK and they should be doing something about it.
 
Probably somebody in China found an alternate goop that was way cheaper and substituted it for the manufacturer spec. Everything from electronics to wood flooring is coming out of China containing things we wouldn't allow in North America. Too bad you can't pull things apart at the store before you buy them.

UPDATE: It's been a couple of days and I am happy to report that the speakers are still working well!

KRK's are guaranteed for 3 years per this:http://www.krksys.com/krk-product-warranty.html
Therefor, if you bought a 2 year exended warranty from GC, then you should have another year on your warranty.

When I look at the pictures now, it looks like that goop was ejected by capacitors boiling over. Another funny thing is the lack of visible solder on the component legs. If you soldered boards properly some solder would wick up the component legs and be visible topside. The boards are being wave soldered after being stuffed with components. 
 
The repairs you are making are better than the original build quality.

Lynn
KRK's are guaranteed for 3 years per this:http://www.krksys.com/krk-product-warranty.html
Therefor, if you bought a 2 year exended warranty from GC, then you should have another year on your warranty.

 
Oh well.  I fixed the speakers and they're holding up well.  And I got it done in a couple of days rather than a couple of weeks plus the expense of shipping.

ampfixer
When I look at the pictures now, it looks like that goop was ejected by capacitors boiling over. Another funny thing is the lack of visible solder on the component legs. If you soldered boards properly some solder would wick up the component legs and be visible topside. The boards are being wave soldered after being stuffed with components.

 
It's not capacitor dielectric unfortunately.  That would have been better, and it probably wouldn't have conducted in the manner in which it did.  It would have just been messy.  I remember I fixed an old copy machine many years ago, and the goop slopped out by a BIG failed capacitor was a weird silicone-Teflon mix.  Syrupy but extremely slick when wiped clean and dried!  Depends on the capacitors though.  Not all are "wet" inside.
 
The goop is stuff to hold components and wires in place...like a hard tar.  I've seen this used on other boards, but it's mostly a white caulk or straight silicone.  Either one is better than this garbage.  This stuff probably dries fast, so it was used on the PCB assembly line for that rapid-fire production.
 

ampfixerThe repairs you are making are better than the original build quality.

 
I agree!  Thanks for the support!

 
Well, this was a fascinating story which I only just now read in its entirety.  Glad things worked out in the end.  You've given us several things to keep in mind as we go forward.
 
Thanks for taking the time 2:43AM  (and be sure to let us know if anything changes )
 

Hi, Mr. « 2.43 AM »
 
At the very beginning of this post last year, you wrote : “I am very familiar with board-level components, troubleshooting, repair, circuit design, soldering, etc. (… ) My real job, however, has nothing to do with circuits and repair!”
 
My situation is not far from yours, the difference being that I probably forgot much of my knowledge about electronic circuitry. Anyway, let’s go to my point:
 
I currently have the same problem with one M-AUDIO BX5A amplified speakers : its tweeter crackles at medium-high volume & frequency. I diagnosed that it comes definitely from the circuitry of one of my speaker. I disassembled its monitor case, the wiring is neat and no apparent bad BGoD.
 
MY QUESTION:  you did not explain how you identified which capacitor, resistor or chip is defective. On my circuitry board, there are approximately 40 components (resistors, capacitors, chips), and all seem neat, none of them bulges. So, how should i proceed to identify the failing component(s) ?
 
I join other people to thank you for the time you spent to share your knowledge.
 
I hope you can answer my question
 
Nicolas
 
Windows 7, Cakewalk UA-25EX external sound card, two M-AUDIO BX5A speakers

Nicolas59 
MY QUESTION:  you did not explain how you identified which capacitor, resistor or chip is defective. On my circuitry board, there are approximately 40 components (resistors, capacitors, chips), and all seem neat, none of them bulges. So, how should i proceed to identify the failing component(s)?

First and foremost...THANKS!  For my failed components, they were visually identified as highly likely to have failed.
 
 
When troubleshooting any faulty electronic circuit/device, start from what can be observed: sights, sounds, smell, touch.  Are there any burnt or discolored components?  Are there sounds that lead you to a particular section of the PCB or component?  Does the problem start and go away after awhile?  Does anything smell "hot" or burnt?  Do any components feel warm or hot?  CAUTION: always be aware of high-voltages which could shock you, i.e. be especially careful around "mains" voltages, amplifier rails, switching power supplies, and high-voltage capacitors.  Obviously, you don't want to be touching these while energized, and some capacitive circuit retain a charge.
 
This is the stage in which I found the bulged capacitors, which were identified to be a highly likely source of circuit failure...electrically.  I say this because at this point, you would have determined the capacitor to be physically failed, but electrically it may still hold up and allow the circuit to operate within its design parameters.  So without further testing of the capacitor, such as ESR and capacitance tests, you would never know the complete "truth."  So the next logical step is to replace what appears to be failed and retest.
 
Following up to visual checks on the components, and certainly something to check before ordering components, is to visually check the printed circuit board itself, all solder traces, and all soldered connections.  Hairline fractures, cold solder joints, and bridged pads can all lead to problems.  To check for loose connections due to loose components, try lightly pressing on components or parts of the PCB while the circuit is turned on, again being careful around hazardous voltages.  You may hear the problem stop or get worse.  As a follow up, use a magnifying glass to inspect around the PCB.  I use a 10x loupe.
 
In your particular case, you have observed the static coming from the tweeter.  So trace the wires from the tweet back to the PCB.  In most cases, and good board design, the various circuits (and its components) are grouped together.  So chances are, the fault component will be relatively nearby the wires going to the tweeter.  I wouldn't rule out an amplifier failure, but hopefully you can replace some basic components for the fix.
 
Another troubleshooting practice is to check voltages with a meter and/or oscilloscope.  But unless you have a schematic and/or component datasheets available (as well as the tools), are versed in electronics, then I would refrain from doing this.  It's not for the faint of heart!  When a device is powered up, one can easily hurt the components, the board, or themselves!
 
I'm proud to say that I successfully brought an Alesis A6 Andromeda back from the dead by repairing it myself, a feat that's was both daunting (since I took the risk of buying a dead one) but also highly-rewarding.  You may read about it here if you wish https://www.gearslutz.com/board/electronic-music-instruments-electronic-music-production/985035-troubleshooting-alesis-a6-andromeda-no-boot.html), and the thread spurred other great troubleshooting by other people, reviving a few more dead Andromeda's:
 
Feel free to PM me any questions, and I will certainly help you out with the repairs!

Nicolas59
I currently have the same problem with one M-AUDIO BX5A amplified speakers : its tweeter crackles at medium-high volume & frequency. I diagnosed that it comes definitely from the circuitry of one of my speaker.

I can't hear the type of crackle you're talking about, so what leads you to believe that the circuitry is at fault and not the tweeter itself ?
 
If you're not sure, you could always swap it with the other tweeter to elliminate the possibility.
 
 

My answers to both Paul and 2:43AM,
(please apologize for my silence for the last week, I was quite busy)
 
to Paul: yes precisely that is what I did, swapping the tweeter.. and the noise "did not swap". I also swapped left and right channels from my Cakewalk sound card. Same? That is how I came to my conclusion.
 
to 2:46AM: thanks for your comprehensive answer. My next steps will be to do these two tests that you suggested : (i) checking component temperature when in use, (ii) gently pressing on components when playing to see if it impacts the noise.
 
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.
 
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 ?