KVR Audio

Rowan88 · Post by **Rowan88** » Thu Jul 27, 2017 7:07 pm

Hi,

I have a pair of Rokit RP5 G2 active monitors but one of them when you power it on makes a horrible loud buzzing sound.

https://sendvid.com/rsojf518

I tried swapping the speaker/woofer out from the other one and it was fine so it has to be something to do with the motherboard inside.

I had a quick look but I couldn't see anything obvious. What would be causing this and what should I look for.

Would this cost a lot to repair?

Thanks

Rowan88 · Post by **Rowan88** » Thu Jul 27, 2017 7:14 pm

https://ibb.co/mW5uc5
https://ibb.co/dPeWPk
https://ibb.co/hqWZc5
https://ibb.co/m1mxVQ
https://ibb.co/hq4HVQ

Some added photos I took.

ere2learn · Post by **ere2learn** » Thu Jul 27, 2017 10:15 pm

Is that melted in those pics?

VariKusBrainZ · Post by **VariKusBrainZ** » Thu Jul 27, 2017 11:02 pm

Looks like moisture

JCJR · Post by **JCJR** » Fri Jul 28, 2017 12:18 am

Hard to tell from the pics on my 7" pad. A couple of pics look like streaks of burned circuit board, but maybe something else. The little dots could be splatter residue of a burned/exploded part, or real sloppy soldering left lots of little dots of residual flux, or maybe something else.

Does the circuit board smell burned? Even if it smells strongly burned then maybe a good repairperson could still fix it. I don't know nowadays how common is component level repair. The art of replacing a part or two on a board rather than simply replacing the entire board. Long ago it was easy to find people who could diagnose and fix a circuit board rather than just order a replacement board. Maybe it is still common, dunno.

I suspect component-level repair may have become rarer because ferinstance if a tech spends 2+ hours locating and replacing a ten cent bad part, maybe the bill is $200+ labor plus ten cents part plus tax. If labor is likely to cost more than a new replacement board then it may not make economic sense looking for the bad parts on a bad board.

If some of the board itself is actually burned, then it will probably be more involved than just replacing a couple of bad parts.

"Board caught fire" is not real common but I've seen it a few times in the past. I remember one time, failure caused a power resistor to overheat, carbonizing the fiberglass board nearby. The carbonized fiberglass turns into a carbon resistor, current flows thru the burned piece of board, it gets hotter and catches fire.

In a (rare) case like that, if determined to repair the board, need to take a nibbler tool and trim out all the carbonized board, then maybe glue some perfboard in the gaping hole, and do point to point wiring to re-create the ruined part of the circuit. Got to remove the burned sections of fiberglass because those are unwanted extra resistors in the circuit.

Maybe your damage is much less severe. Tis hard to tell looking at the pictures.

BertKoor · Post by **BertKoor** » Fri Jul 28, 2017 7:10 am

Rokit series are cheap. For a reason. You just discovered it. Build quality issues.

Now is a good time to upgrade to something better....

Rowan88 · Post by **Rowan88** » Fri Jul 28, 2017 12:48 pm

The black in the photos breaks off and feels like some sort of glue or rubber.

Rowan88 · Post by **Rowan88** » Fri Jul 28, 2017 12:54 pm

Sorry couldn't see where to edit..

I have taken the motherboard part out and when I plug just that into power it powers but but no noise issues. And the fact I tried the speaker/woofer in another unit and it worked this tells me its something to do with motherboard in relation to connecting up the speaker/woofer?

I will upload some more detailed pics hopefully to show any issues..

Rowan88 · Post by **Rowan88** » Fri Jul 28, 2017 1:02 pm

https://ibb.co/dcSHh5
https://ibb.co/kqKV25
https://ibb.co/mHpKvQ
https://ibb.co/gqfg9k

This is it with the two large capacitors removed:

Tried removing and reseating both capacitors and the red/black cable that goes to the speaker.. but still same problem

BertKoor · Post by **BertKoor** » Fri Jul 28, 2017 2:26 pm

Electronical problems like this cannot be diagnosed from photos. We need to poke around in it with a multimeter and scope, look for components that don't function but still look good from the outside.

Would this cost a lot to repair?

I estimate about as much as just buying something new. Experts will charge $50 for just screwing off the back and put it back on.

How long have you had them now?

Rowan88 · Post by **Rowan88** » Fri Jul 28, 2017 2:40 pm

I have had them a good 4 years but I stopped using them because of this issue. Decided to open it up incase it was just a simple part that blown and that I could replace

If I get a multimeter what parts should I be checking?

Also this is a photo of my "working" monitor, and it doesn't look much different:

DIRECT LINK: https://ibb.co/d0JwaQ

BertKoor · Post by **BertKoor** » Fri Jul 28, 2017 3:17 pm

Rowan88 wrote:I have had them a good 4 years

Twice the warranty period, so that's good. Meanwhile you should have put a tenner in a jar each month, so now you can buy something better!

Rowan88 wrote:If I get a multimeter what parts should I be checking?

What about all of them?

Resistors should have the labelled resistance
Capacitors should have the labelled capacitance
Transistors should have the labelled, ehrm... transistance?

vegaron · Post by **vegaron** » Fri Jul 28, 2017 3:44 pm

You can not measure resistors and capacitors without separating them from the whole circuit. You would measure the resulting resistance or capacitance of a lot more parts than just the one you think you check...
In the circuit you can just check for voltage levels, which may tell you a lot though.

JCJR · Post by **JCJR** » Fri Jul 28, 2017 6:40 pm

Either board-level repair or component-level repair is best practiced as an orderly diagnostic process. First testing for the simplest/easiest problems, then progress step by step until the problem is localized. Both with hardware repair or software debugging, it is usually a mistake to start fixing stuff until you have a real good first guess what is wrong.

It is an interesting topic to learn, but perhaps wasted effort if you are not interested in studying the skill, and you just want to fix the speaker. On the other hand if you want to become knowledgable of hardware repair, attempting diagnosis/repair on your speaker may be valuable learning practice. Practice and experience IMO is more important than book learning to be a repairman. Of course theory is also important.

I remember decades ago an acquaintance had just got his BS EE and needed some money for awhile until he found a real job. I was getting more stuff brought in than I had time to fix, so said he could keep all the fees of whatever he would repair. The problem was, he didn't know how to repair mixers, fx, amps, etc. I was too busy to coach him so it didn't work out. He knew more EE than I did, but they had not taught him how to fix anything! He could have learned given some practice. He just hadn't yet learned how.

Perhaps the first skill to learn is how to avoid accidentally electrocuting yourself. The highest priority!

From the symptoms it could be just about any combination of bad parts on the board. Dunno whether that is an analog or digital amp? If analog does it use integrated power amp chips, or does it use discrete power transistors? It could be bad parts in the power supply. It could be a blown opamp or transistor in the input stages.

If both the tweeter and woofer buzz, and it is a biamp speaker, it might be an input stage or power supply issue. Could also be fried power transistors or integrated power amp chips. If its a digital amp, I never studied how to fix digital amps.

Switching power supplies and digital power amps can have much higher voltages in there than mid-power analog amps, deserving more caution.

You need a pretty good multimeter with high impedance, several megohm input impedance in the voltmeter mode. Most cheap meters are high impedance nowadays, but you can still buy low impedance cheap meters used for occasional hobby auto or house wiring purposes. If you stick a low impedance meter at certain points in a solid state analog power amp, just touching that unfortunate point can unbalance the circuit enough to instantly fry all the power transistors. That is why you want a high impedance multimeter.

It is also easy to make problems lots worse if you are not steady with the probes. Testing with power on, there will be places in a circuit if you accidentally touch the probe to two adjacent pads, shorting them together, you can instantly fry lots of semiconductors that were not bad until that slip of the hand.

Turning a possibly simple repair into a nightmare.

Some guys are talented enough to fix about anything with just a multimeter. When I was working on mixers, fx, amps, etc, the tools I'd want, simply because I'm not naturally talented enough to just use a multimeter (maybe am forgetting an item or two, dunno)--

Multimeter
Oscilloscope
Signal generator
Variac
Curve Tracer
A pair of at least 300 watt low inductance 8 ohm load resistors

Rowan88 · Post by **Rowan88** » Sat Jul 29, 2017 9:08 am

I tinkered about a little more this morning. I tried removing the two large black capacitors and also the one on R108 (small white/red one) and swapped them with ones I know are ok from my working unit. The problem persisted so I can rule them out?

Is there any other components I should have a look into swapping with the working unit to narrow down what the faulty part could be?

KRK Rokit RP5 Buzzing