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KRK Rokit 8s - One crackles
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beedoola
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#1
18th December 2012
Old 18th December 2012
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KRK Rokit 8s - One crackles

I posted another thread about them blowing fuses. I bought these used for cheap cause of the fuse issue, I resolved that but now have a crackling issue with one.

I replaced the Filter caps and resistors near them. Worked alright but now I'm getting some crackle and pop from the speaker and now a little from the tweaker. Happens even with the volume turned down on the monitor. The sub speaker jumps a bit - in and out, not constantly.

I replaced the output amplifier (the 100W that mounts to the heatsink) on the other monitor, as well as the filter caps and resistors and that one is fine.

The output amp on the monitor in question seems to be alright - the other was blown and I could test with the meter, this one seems ok.

thoughts?
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18th December 2012
Old 18th December 2012
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Crackle/pops indicate a failing component (poweramp), or dryjoints on the circuit board.
Power amp pin dryjoints are common.
It could also be a leaking cap. Acid, or acid residue on the circuit board also causes crackling noises. Clean with alcohol.
Check the polarity of the caps that you have replaced.
Leo..
beedoola
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18th December 2012
Old 18th December 2012
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Quote:
Originally Posted by LeeYoo View Post
Crackle/pops indicate a failing component (poweramp), or dryjoints on the circuit board.
Power amp pin dryjoints are common.
It could also be a leaking cap. Acid, or acid residue on the circuit board also causes crackling noises. Clean with alcohol.
Check the polarity of the caps that you have replaced.
Leo..
Hey Leo,

The filter cap polarities are fine. Can a failing power amp - I'm guessing you mean the 100w output device, still work before it fails?

There are maybe two or three small electro caps between the output pin of the output amp/device and the positive lead to the speaker. I haven't replaced those yet but was thinking maybe those might be it.
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18th December 2012
Old 18th December 2012
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Quote:
Originally Posted by beedoola View Post
Can a failing power amp - I'm guessing you mean the 100w output device, still work before it fails?
For sure. I had a similar issue with the same monitors back in 2003 or 4.
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21st December 2012
Old 21st December 2012
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We have repaired several of these speakers now. They are quite badly designed and even more badly built. The schematics we were given do not match what is on the pcb. It is most likely the power amp chip, or at least it needs to be eliminated by replacing it. It could also be a bad joint. The boards on the ones we have seen are covered in this black glue shit which makes it very hard to service. Good luck !
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21st December 2012
Old 21st December 2012
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Hi Tim.
This black ados-F2 like glue can also be found in consumer audio etc.
I always got it off by wetting it with a cotton bud, drenched in acetone, and letting it soak for a while.
Then you can peel it of like a piece of sunburned skin.
Sometimes, with older gear, the tracks are rotted away underneath.
Leo..
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21st December 2012
Old 21st December 2012
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Quote:
Originally Posted by Tim Farrant View Post
We have repaired several of these speakers now. They are quite badly designed and even more badly built. The schematics we were given do not match what is on the pcb. It is most likely the power amp chip, or at least it needs to be eliminated by replacing it. It could also be a bad joint. The boards on the ones we have seen are covered in this black glue shit which makes it very hard to service. Good luck !
They dont sound that great either
beedoola
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22nd December 2012
Old 22nd December 2012
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Quote:
Originally Posted by Tim Farrant View Post
We have repaired several of these speakers now. They are quite badly designed and even more badly built. The schematics we were given do not match what is on the pcb. It is most likely the power amp chip, or at least it needs to be eliminated by replacing it. It could also be a bad joint. The boards on the ones we have seen are covered in this black glue shit which makes it very hard to service. Good luck !
One monitor is a a Blue PCB, the other - the one in question is Green.

So I replaced the output device and the surrounding components that touch the Output trace that leads to the positive lead for the sub; two electro caps (one is non polar) and two other np caps. The monitor worked fine for a bit then I got a loud pop and it seemed the tweeter blew - or thought it did.

I removed the front plate, seems the negative lead for the tweeter may have been loose. Put it back together and then it worked fine. Then later after turning it off and then coming back to play again, the monitor wouldn't produce sound.

Would a faulty connection with the power cause this? Would a faulty power connection cause the fuse to blow? - cause the fuse isn't blowing, the monitor stays on. But I had the back of the amp off and had it connected, using my plastic poking stick to touch the PCB trace and components to see if anything was wrong.

The amp seemed to work again but I think - not totally sure, I touched the power cord with my foot and the amp went silent again. I tried replicating it but cannot.

Someone also mentioned checking the input rectifier, where might that be located in the amp?

Thanks to everyone for weighing in, I appreciate it.

Quote:
Originally Posted by jeremycox View Post
They dont sound that great either
For $50 and me being nearly broke, they'll do.
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beedoola
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26th December 2012
Old 26th December 2012
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Quote:
Originally Posted by jeremycox View Post
For sure. I had a similar issue with the same monitors back in 2003 or 4.
what were some of the symptoms?

Since my last post I've gone over all the solder joints I've redone - where components were replaced and touched up a few traces that I hadn't touched but where (presumably) stock solder joints.

The sub puts out zero signal. If I disconnect the tweeter and leave the sub plugged in (powering the monitor down first before doing that, of course) I get no sound. With the tweeter plugged it, sound comes through but its super high in frequency bands - not sure if thats how it is supposed to be stock.

I've checked the filter cap voltages - both 37v. I'm stumped and feel defeated
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