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Old 2nd December 2017
  #5
Q&A Session

The following are notable Q&A's from original thread and have been ported over into this new thread on GS. I hope you find them helpful.

Quote:
I emailed KRK, or more accurately, Gibson, to ask for a quote for a repair or if they would be able to advise me on components to replace damaged ones with and they passed me on to Focusrite who they said handled their repairs.
Focusrite then replied passing me on to another company who apparently handle their repairs. The third company has not responded -_-


Quote:
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).
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?

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!

Quote:
Can you post a link to the 2.2kΩ, 1/2W carbon film resistors that you got from Digi? I don't know which one to buy
thanks!!
CFR-50JB-52-2K2 Yageo | Resistors | DigiKey

Helpful tip from CW member Ampfixer: "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."

Quote:
When I look at the pictures now, it looks like that goop was ejected by capacitors boiling over.
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. However, most capacitors are "dry," including the ones used in the Rokit speakers.

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 one-of-a-kind, rapid-fire production!

Quote:
You sure?

Positive. That's the BGoD. Eradicate it immediately.

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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?
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.

Quote:
I want to repair my rokit 8's with the same issue but i am a little worried that i might kill them. What are the chances of overheating when soldering with these components? I have killed a few components before because of this but dont want to risk too much with my monitors...
It depends on what you're desoldering and soldering. If repairing integrated circuits (IC's) and "chips," then component package overheating and damage must be considered. Temperature and time are an IC's worst enemy. Many component datasheets specify a maximum temperature sustained for a particular length of time, e.g. 10 seconds at 250°C (482°F). This mainly is a guideline for PCB manufacturers that use solder wave machines and reflow ovens. However, you may also use these maximums while manually soldering and desoldering components. With practice, technique, prep work, and the right tools and temperature, you should be able to solder a pad in a few seconds. For passive components (resistors, capacitors, and inductors), heating should be considered, but it is not as critical.

Quote:
Also I have a hum in one of them along with the crackling, could this be caused by the same problem?
it sounds like ground hum, but when i switch the speakers power supply (swap the IECs, keeping them plugged up the same and with no audio cable plugged in) the hum stays in the same speaker, so i assume it is a problem with the speaker itself...
This, no doubt, sounds like the goop is causing the hum and the crackle. Open up the speaker and inspect for the stupid, corrosive and conductive goop they slathered all over the board. Also check for failed capacitors. You'll be crackle-free in no time!

Quote:
How do you recommend cleaning the goop off? i picked at it a little with a flat head driver and its harder than I expected it to be. Did you just chisel it off?
Cleaning the goop will require something to soften it (chemicals, soldering iron tip, i.e. heat, etc.), then you must scrape it off. Be careful of the traces and surrounding electronic components.

Your biggest concern is actual damage to the circuit board itself...mainly in the melting of the glue layer that holds the copper pad and/or copper trace to the board. If overheated, then this glue melts and the pad and/or trace can lift off the board. Worst case is when it breaks. In my experience, much time needs to be spent working, reworking, and working a pad/trace in order for this to happen. When in doubt, let it cool!

Quote:
So I opened up my monitor. As far as I can see my caps are OK except the one in front of the TDA7296. How should I check the IC condition? I only have a multimeter on hand. Or should I just start cleaning up the black goop?
I would just start cleaning the goop. IMO, don't worry about the amplifier IC. When in operation and powered up, you risk seriously shorting out the component.

Helpful tip from CW member Neilbags: "I'd clean up the goop. Replace the damaged resistors and diodes, clean and test the caps with an ESR meter."

Quote:
Why do these speakers suck so badly?
It's amazing to see the disgusting and negligent spread of the BGoD all over the PCB and components. There is absolutely no reason that crap should be where it is. It's not holding any thing down. It's not preventing vibration of tall components. What a horrible mess of "craftsmanship!" Conspiracy theorists could suspect planned failure/obsolescence of the entire board so the speakers would require repair and/or replacement. Complete joke!

Quote:
...but the most interesting thing I found is I can make the speaker operate normally by bending the PCB towards the bottom side. Works 100% of the time. And if I bend it up upwards towards the component side it creates the noise again.

Czech my vids: Video 1 and Video 2
Good information and a clue! This is a classic symptom of a cold-solder joint and/or or a broken trace.

Quote:
I'm afraid that i've shorted some components somehow because the last time i started it up only the tweeter works. I'll source some acetone then for now.
From my experience, this is actually a symptom of The Black Goop. I thought both of my amplifiers were smoked, but upon cleaning the goop, replacing a few capacitors, the speakers came back to life and have remained strong and problem free ever since.
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Additional photos and attachments below, depicting the sheer destruction and corrosion caused by the BGoD, courtesy of piss-poor craftsmanship!
Attached Thumbnails
Shade-Tree Repair Guide: Fixing the Crackling/Static in KRK Rokit peakers-additional_bgod_photo1.jpg   Shade-Tree Repair Guide: Fixing the Crackling/Static in KRK Rokit peakers-additional_bgod_photo2.jpg   Shade-Tree Repair Guide: Fixing the Crackling/Static in KRK Rokit peakers-replaced_caps1.png   Shade-Tree Repair Guide: Fixing the Crackling/Static in KRK Rokit peakers-replaced_caps2.png