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Repair a KRK 10s Subwoofer - parts id

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spec

Well-Known Member
Most Helpful Member
Hi chinjazz,

Welcome to ETO.

I see that you are from the US. Which State? If you put it next to 'Location' on your user page it will show in the box at the left of your posts. Not only is it interesting to know where people are, but it also helps us answer your questions: time zone, native language, mains supply, component access, safety standards...

spec
 

spec

Well-Known Member
Most Helpful Member
Hi again chinjazz,

Sorry to hear about your bass sub failure. The good news is that bass subs are relatively simple and tend to use standard components that are freely available, and low cost (especially as you are located in the US- in some countries getting electronic components is a nightmare).

The other good news is that there are a number of ETO members experienced in audio.

But may I suggest that you post all of the information about your problem here on ETO. The pictures on your link above are not too clear.

Remember that the more information you can provide, the more chance that we can get your sub fixed between us. If you know of a link to the service manual that would me a major help too as would some well focused pictures of the whole unit and detailed picture of the entire board.

Just one last point: with any fault it is always essential to correct the root cause of the failures- just replacing blown components will not help, as you have found.

Apologies for being a nag.:D

spec
 

chinjazz

Member
Hi Spec,

Thanks for the sound advice!

I'll start fresh here with more details that should help my situation.

I bought this used Subwoofer and it was working "fine" with the exception of a bit of intermittent audio "crackle" on start up,
and sometimes for a minute or so until it warmed up.

I took the unit apart for a visual inspection, and found a Diode was visibly showing issues.
Here's a pic of the unit first apart (Issue is where the Diode is installed):

IssueLocation.jpg

Up Close of the Diode:

badboy1.jpg

First Action: Sprayed the area with contact cleaner (not knowing I should have tested the diode itself).

After I re-installed, and fired up the unit.. The power light goes on, and there's clearly no audio.

However, interestingly enough, since it's a Sub, and has outputs to 2 studio monitors, there is signal going thru, and I can hear
those monitors (just no sub).

After disassembly this time, I removed the Diode to inspect it. It broke in half. I removed a 2nd Diode so I could identify what it was, and luckily found a package of replacements at a local Radio Shack.

I replaced the 2 Diodes (got savvy and tested them both with my VM which has a diode setting).

Plugged in, and still no sub audio. Everything else was good (power, and monitor signal).

Then I took it apart again, and noticed this (which I may have missed the first time). Lesson to be learned here (my thought):

2. OtherSide.png

Two Resistors on the other side after a bit of clean up:

3. CleanedUp.png

In context this is where this is on the board:

6. BoardWithNotes2.png

I also took some images of the whole kit in context to this board.

Back Panel:
1. BackPanel.jpg
Back Panel Side:
2. BackPanelSide.jpg
Inside (showing the power - volume control board / pre):

3. InsideFromBackPanel.jpg

The other side from that (the ins/outs):

4. AudioInputBoard.jpg

From a reference stand point, I haven't found a service manual yet, but here are a few links:
http://www.krksys.com/krk-subwoofers/10s.html

The one I own is 1 rev back than the one listed above.

Here’s a PDF of the manual (page 18 has the specs which are not detailed enough):
http://www.krksys.com/manuals/subwoofers/MANUAL_KRK10S-D_Web.pdf


I found that @ Full Compass it’s possible to buy a completed Replacement Amp Assembly here:

http://www.fullcompass.com/prod/259996-KRK-AMPK00055

Hope all this is useful!
 
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spec

Well-Known Member
Most Helpful Member
Well well CJ,

Many thanks for the above post. That is excellent and give a clear view of what is going on.

spec
 

spec

Well-Known Member
Most Helpful Member
You have been very cooperative so dare I ask just a few more questions which will be a help.:D

What are your skills in electronics.
Can you unsolder and remove electronic components and also fit components.
Do you have a small pair of pliers and wire cutters.
Do you have a small soldering iron and solder
Do you have a multimeter and know how to make basic measurements.

Once again, apologies for all the questions.

spec

By the way do not turn your bass sub on again until we advise further or you stand to blow the speaker.
 

chinjazz

Member
Well well CJ,

Many thanks for the above post. That is excellent and give a clear view of what is going on.

spec
Hey Spec, I'll complete the post above (was editing it, and previewing - gathering pics), and I posted it accidentally.
I'll finish it up in about an hour, and re-send.

Thanks
 

chinjazz

Member
You have been very cooperative so dare I ask just a few more questions which will be a help.:D

What are your skills in electronics.
Can you unsolder and remove electronic components and also fit components.
Do you have a small pair of pliers and wire cutters.
Do you have a small soldering iron and solder
Do you have a multimeter and know how to make basic measurements.

Once again, apologies for all the questions.

spec

By the way do not turn your bass sub on again until we advise further or you stand to blow the speaker.

No worries whatsoever, I much appreciate your attention.

I replace guitar parts and wire up pots, resistors fairly routinely. Got a few irons, and now have some smaller tools for these components.
I've got a good enough multimeter to get thru this for sure.

I'm definitely learning what some of these components are. Mustering up some of my past history.
Recording engineering degree required a bit circuit board t-shooting, building..Ohms law stuff also, but that was in the 1980's (LOL).

Thanks!
 

spec

Well-Known Member
Most Helpful Member
No worries whatsoever, I much appreciate your attention.

I replace guitar parts and wire up pots, resistors fairly routinely. Got a few irons, and now have some smaller tools for these components.
I've got a good enough multimeter to get thru this for sure.

I'm definitely learning what some of these components are. Mustering up some of my past history.
Recording engineering degree required a bit circuit board t-shooting, building..Ohms law stuff also, but that was in the 1980's (LOL).

Thanks!
An ideal man. Recording Engineer- cool:cool:

I have been designing and building amps and speakers for years and have a couple of guitars: Strat clone and Yamaha acoustic six steel string. And friend has a musical equipment repair workshop. He is also a base player in a couple bands. He has instruments all over his place in the country.

Back to your sub. I am surprised how many boards there are. The one with the fault on looks like the power amplifier board so the first thing to do is to protect the speaker.

(1) Can you disconnect the speaker, and measure the resistance of the voice coil or voice coils if it has more than one.
(2) Then push the speaker cone in and make sure it moves freely and does not make a scraping sound.
(3) Connect and disconnect a 1.5V battery (U2 would be ideal) to the speaker voice coil. You should hear a 'bong' type sound.
(4) If all is well you then need to protect the speaker. To do this connect a 5 watt or higher 10 Ohm resistor (the resistance value is not critical) in series with the speaker.

We can then get down to the business of finding the fault.

spec
 

chinjazz

Member
An ideal man. Recording Engineer- cool:cool:

I have been designing and building amps and speakers for years and have a couple of guitars: Strat clone and Yamaha acoustic six steel string. And friend has a musical equipment repair workshop. He is also a base player in a couple bands. He has instruments all over his place in the country.

Back to your sub. I am surprised how many boards there are. The one with the fault on looks like the power amplifier board so the first thing to do is to protect the speaker.

(1) Can you disconnect the speaker, and measure the resistance of the voice coil or voice coils if it has more than one.
(2) Then push the speaker cone in and make sure it moves freely and does not make a scraping sound.
(3) Connect and disconnect a 1.5V battery (U2 would be ideal) to the speaker voice coil. You should hear a 'bong' type sound.
(4) If all is well you then need to protect the speaker. To do this connect a 5 watt or higher 10 Ohm resistor (the resistance value is not critical) in series with the speaker.

We can then get down to the business of finding the fault.

spec
Awesome! I've had my share of tech in the Music industry. I used to be the web master guy for Aguilar Amplification.
It's current incarnation still has my tech fingerprint on it :). I'm out of work currently (why I've go time on my hands to do this project).

Musician tech's are the best!

Thanks for these first steps.. Quick question: Why would I need to protect the speaker? To t-shoot it live/hot?
I've got to go back to Radio Shack anyway sometime today or tomorrow.

Thanks,
CZ
 

spec

Well-Known Member
Most Helpful Member
Why would I need to protect the speaker? To t-shoot it live/hot?
You should always protect the speaker. It is the most expensive part in the the unit.

A faulty power amp can put some killer power into your speaker, either DC or, if the amplifier is oscillating, AC, sometime very high frequency which will take your speaker coil out in a f;lash- I speak from much experience.:banghead:

By putting a resistor of roughly twice the impedance of the speaker coil in series with the coil you limit the amount of power that the speaker can get. The speaker is thus protected.

spec
 

chinjazz

Member
You should always protect the speaker. It is the most expensive part in the the unit.

A faulty power amp can put some killer power into your speaker, either DC or, if the amplifier is oscillating, AC, sometime very high frequency which will take your speaker coil out in a f;lash- I speak from much experience.:banghead:

By putting a resistor of roughly twice the impedance of the speaker coil in series with the coil you limit the amount of power that the speaker can get. The speaker is thus protected.

spec

Thanks spec, that does make sense.

I'm wondering if this resistor should stay for good, or remove later after testing?
I'll make that visit to Radio Shack today. Those 1.5 v batteries (I never had one in hand), might you have a link to one on Amazon or elsewhere so I can get a reference point? U2?

Are there any other parts I'll need for testing while I'm there (at minimum for today)?

(sorry I didn't reply quicker yesterday, I was busy doing job search things)

cz
 
Last edited:

chinjazz

Member
An ideal man. Recording Engineer- cool:cool:

I have been designing and building amps and speakers for years and have a couple of guitars: Strat clone and Yamaha acoustic six steel string. And friend has a musical equipment repair workshop. He is also a base player in a couple bands. He has instruments all over his place in the country.

Back to your sub. I am surprised how many boards there are. The one with the fault on looks like the power amplifier board so the first thing to do is to protect the speaker.

(1) Can you disconnect the speaker, and measure the resistance of the voice coil or voice coils if it has more than one.
(2) Then push the speaker cone in and make sure it moves freely and does not make a scraping sound.
(3) Connect and disconnect a 1.5V battery (U2 would be ideal) to the speaker voice coil. You should hear a 'bong' type sound.
(4) If all is well you then need to protect the speaker. To do this connect a 5 watt or higher 10 Ohm resistor (the resistance value is not critical) in series with the speaker.

We can then get down to the business of finding the fault.

spec
Hey Spec,

When you said a 1.5v battery (U2 would be ideal), what kind of battery do you mean?
I went to Radio Shack, and realized I didn't know what U2 meant..

Thanks!
CZ
 

spec

Well-Known Member
Most Helpful Member
Hi CJ,

I'm wondering if this resistor should stay for good, or remove later after testing?
The resistor is only put in series with the speaker for testing or if you suspect a fault somewhere. It is just a wise precaution. Once the system is working OK again the resistor should be removed as it reduces acoustic output power and messes the frequency response of the speaker.
Are there any other parts I'll need for testing while I'm there (at minimum for today)?
Afraid not sure at the moment
When you said a 1.5v battery (U2 would be ideal), what kind of battery do you mean
It's the fat flashlight battery. Maybe they are not called U2 in the States. Any decent sized 1.5V battery will do though even an AA size. It is just to push some current through the speaker voice coil to ensure that the speaker is still working.

spec
 
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chinjazz

Member
Yep, speaker is good. Got a 3.5 - 3.6 reading - must be a 4 Ohm spkr.. Tested it with the battery also, sounds good (awesome).

I'll solder on the resister to one terminal end then I'll be ready to proceed :)
 

spec

Well-Known Member
Most Helpful Member
Yep, speaker is good. Got a 3.5 - 3.6 reading - must be a 4 Ohm spkr.. Tested it with the battery also, sounds good (awesome).

I'll solder on the resister to one terminal end then I'll be ready to proceed :)
Good. I thought the speaker may be 4 Ohms.

spec
 
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