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Shade-Tree Repair Guide: Fixing the Crackling/Static in KRK Rokit peakers
Old 13th September 2020
  #61
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Quote:
Originally Posted by Athhos View Post
Great fault finding report and sharing.
I've a KRK RPG2 8 and similar issues.
Let's see if I can make it ok.
Regards.
First I removed the big capacitors (2 x 3300uF/50 and 2 x 1000uF/35V).
Then, I've used paint stripper (https://www.lowes.com/pd/Klean-Strip...-qt/1000659649) to remove the BGoD from the boards - both the amplifier and pre-amp with the potentiometers. Brushed a thick layer and after 15 min the BGoD melted away. Then washed them with DAWN blue soap thoroughly using a toothbrush under lots of water (lukewarm) and dried them with a hair drier.
It cleaned them beautifully and exposed all corroded wires or terminals.
Had to replace one diode - 1N4148, the 2K2 resistor 1/4W, and one green 100nF capacitor.

Now the sound is back, full bass and highs.
Old 13th September 2020
  #62
Here for the gear
 

Quote:
Originally Posted by lordhex View Post
First I removed the big capacitors (2 x 3300uF/50 and 2 x 1000uF/35V).
Then, I've used paint stripper (https://www.lowes.com/pd/Klean-Strip...-qt/1000659649) to remove the BGoD from the boards - both the amplifier and pre-amp with the potentiometers. Brushed a thick layer and after 15 min the BGoD melted away. Then washed them with DAWN blue soap thoroughly using a toothbrush under lots of water (lukewarm) and dried them with a hair drier.
It cleaned them beautifully and exposed all corroded wires or terminals.
Had to replace one diode - 1N4148, the 2K2 resistor 1/4W, and one green 100nF capacitor.

Now the sound is back, full bass and highs.
It looks like mine.
But mine big caps for subwoofer are from 4700uf 50V (maybe because is rokit 8 and not 6). I'm planing to change all electronic components in the BGoD area including 1/8 resistors and diodes.
Let's how it goes in the end. Isopropilic alcool is the best to use in electronic pcbs.
Thanks for the feedback.
Old 1 week ago
  #63
Here for the gear
 

Hey everyone, thank you for keeping up with this post, it has been very helpful. Maybe you can help me with my Rokit 5 RPG2's. I bought them 2nd hand, knowing that one of them had a high pitch squeal from the tweeter when powered on. The other was supposedly fine, but it was humming and crackling quite a bit. I went ahead and replaced the 2200uf 50v caps and the 1000uf 50v caps on both. I reconnected the wiring and tested them before re-assembling the units, and they both sounded great. After fully re-assembling the speakers and powering them on, they are both blowing fuses right when I power them on. I cannot figure out what changed, other than the heat sinks were not attached to the back plate assembly when I tested them. Any ideas?

Thank you all again for keeping this alive.
Old 1 week ago
  #64
Quote:
Originally Posted by lordhex View Post
First I removed the big capacitors (2 x 3300uF/50 and 2 x 1000uF/35V).
Then, I've used paint stripper (https://www.lowes.com/pd/Klean-Strip...-qt/1000659649) to remove the BGoD from the boards - both the amplifier and pre-amp with the potentiometers. Brushed a thick layer and after 15 min the BGoD melted away. Then washed them with DAWN blue soap thoroughly using a toothbrush under lots of water (lukewarm) and dried them with a hair drier.
It cleaned them beautifully and exposed all corroded wires or terminals.
Had to replace one diode - 1N4148, the 2K2 resistor 1/4W, and one green 100nF capacitor.

Now the sound is back, full bass and highs.
Good job! That paint stripper is a good tip, so thanks for sharing that. However, anyone trying it for their circuit boards: just be careful during the wash stage. Generally, water is OK to use to wash circuit boards--in moderation--as most electronic parts are sealed. Obviously, avoid getting water in potentiometers and other "open" devices. Using RO or distilled water is preferred (devoid of minerals/salts) and drying is absolutely critical before power up. Even the slightest bit of water between traces or pins of a device can cause a short circuit and/or undesired behavior leading to possible damage or a blown speaker.

In the past, I used to wash my custom PCBs with soap and RO water to remove residues of water-soluble solder flux, which if left in place, can cause undesired operation because it is mildly conductive and a bit corrosive. It is considered, I believe, a relatively active form of solder flux compared to a rosin, for example.

Anyway, you did it right, but I thought I would give caution to others.
Old 1 week ago
  #65
Here for the gear
 

So I went ahead and applied the paint stripper to the board and removed almost all of the black goop (thank you for the tip). Washed with Dawn afterwards, let the board completely dry. Re-assembled the unit, and it is still blowing fuses. Something must be grounding out somewhere, but I cannot figure out where. It powers on fine when the power amp board is not attached to the back plate, but as soon as I attach it with the 3 screws and try to power the unit back on, it blows the fuse.

Could it be the caps that I installed? I will try to put the old ones back in and see if that fixes the problem.
Old 1 week ago
  #66
Here for the gear
 

So I put the old caps back, but I still had the same issue. Is there supposed to be some sort of barrier between the heat sink and the back plate, other than that thin piece of nylon?
Old 1 week ago
  #67
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Ok, I think I figured it out. The amplifier chips have a thin plastic insulator between them with thermal paste between that piece if plastic and the heat sink. The thermal paste on mine was completely dried out and crusty. I suspect they used the paste as an additional insulator between the chip and the sink.

In addition to that, the screw fastening the chip to the heat sink has a nylon bushing on it that prevents the screw from making direct contact with the chip. A couple of mine broke when I was removing them to take the heat sink off prior to cleaning the black goo.

I replaced the thermal paste under the plastic insulator, and used the two good bushings I had left to re-assemble the unit. Powered it back on, no blown fuse!

Kind of worked itself out I guess haha. Thank you all anyways for maintaining this thread, much appreciated.
Old 6 days ago
  #68
Quote:
Originally Posted by Mrbungledisco View Post
So I put the old caps back, but I still had the same issue. Is there supposed to be some sort of barrier between the heat sink and the back plate, other than that thin piece of nylon?

Quote:
Originally Posted by Mrbungledisco View Post
Ok, I think I figured it out. The amplifier chips have a thin plastic insulator between them with thermal paste between that piece if plastic and the heat sink. The thermal paste on mine was completely dried out and crusty. I suspect they used the paste as an additional insulator between the chip and the sink.

In addition to that, the screw fastening the chip to the heat sink has a nylon bushing on it that prevents the screw from making direct contact with the chip. A couple of mine broke when I was removing them to take the heat sink off prior to cleaning the black goo.

I replaced the thermal paste under the plastic insulator, and used the two good bushings I had left to re-assemble the unit. Powered it back on, no blown fuse!

Kind of worked itself out I guess haha. Thank you all anyways for maintaining this thread, much appreciated.
Yes, it is typical that the case of integrated-circuit devices with metallic cases/heat-sinks (i.e. TO-220, TO-3, etc.) have one of their terminals as the case itself or shared with another pin. Those little wafers/rubber mats are required to keep the case and the connected heatsink separate. If screwed down, there needs to be a nylon screw or a nylon bushing to provide further insulation.

Glad the fuses worked, saving your amplifiers from letting out the magic smoke!
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