Repair a KRK 10s Subwoofer - parts id

[spec]

What's next on my task list? LOL

Hi CJ,
By looking at the the image, I don't think you have the resistor wired in correctly. Originally two wires were connected to the speaker. If you can imagine removing one wire from the speaker and connecting that wire to one end of the resistor. Then connecting the other end of the resistor to the vacant terminal on the speaker that would be right.

spec

 

[chinjazz]

Hi CJ,
By looking at the the image, I don't think you have the resistor wired in correctly. Originally two wires were connected to the speaker. If you can imagine removing one wire from the speaker and connecting that wire to one end of the resistor. Then connecting the other end of the resistor to the vacant terminal on the speaker that would be right.

spec

Gotcha... Easy enough to change that.

It doesn't matter which terminal side correct?
I put the speaker back in the cabinet.. Is it safe to assume that I'll have all the parts out of the box for this testing?

Thanks!

 

[spec]

It doesn't matter which terminal side correct?

That is correct. But strictly speaking (sorry for pun) the resistor should go in the high side- if there is one (some amps have a bridge output so there is no high side).

I put the speaker back in the cabinet.. Is it safe to assume that I'll have all the parts out of the box for this testing?

Yes, that is correct. You can forget about the speaker now that you have protected it and tested it. Yes, we will be working on the power amplifier board mainly.

Bear in mind that mains voltages will be present on the circuit up to the primary of the toroid transformer (big & round) so please take care.

The next test is to set your meter to DC volts and measure the voltage across the speaker terminals. (it should be 0V to +-0.1V).

spec

 

[chinjazz]

That is correct. But strictly speaking (sorry for pun) the resistor should go in the high side- if there is one (some amps have a bridge output so there is no high side).

Yes, that is correct. You can forget about the speaker now that you have protected it and tested it. Yes, we will be working on the power amplifier board mainly.

Bear in mind that mains voltages will be present on the circuit up to the primary of the toroid transformer (big & round) so please take care.

The next test is to set your meter to DC volts and measure the voltage across the speaker terminals. (it should be 0V to +-0.1V).

spec

Sorry, I'm a bit confused.

I currently have the amp board disconnected from anything else, and measured with the MM and it measured at 0V, and the 2nd try 0.1V.

Is this test set up correctly?

Thanks,
cz

 

[spec]

Sorry, I'm a bit confused.

I currently have the amp board disconnected from anything else, and measured with the MM and it measured at 0V, and the 2nd try 0.1V.

Is this test set up correctly?

Thanks,
cz

Oh I see. I did not realise that the amplifier board was disconnected.

I meant to measure across the speaker terminals with the system fully configured and turned on. Is it possible to do that?

spec

 

[chinjazz]

Oh I see. I did not realise that the amplifier board was disconnected.

I meant to measure across the speaker terminals with the system fully configured and turned on. Is it possible to do that?

spec

I think this is possible... I'd need to get the speaker back out of the box..

I'd assemble it back just like it is in this pic:

I was doing some noodling in thought on this, and the two or one blown resistor at the bottom (where it says "Bad Resistor) - the white connector goes to the pre-amp pcb (even says it on the board), which kind
of now makes sense to me why no sub woofer output is present, but is fine for the two mains (they're going thru).

I do feel the issue is in this neighborhood.

I'll run this next test tomorrow with all the guts on the table.

And of course: I'll Bear in mind that mains voltages will be present on the circuit up to the primary of the toroid transformer (big & round) so please take care.

I'll make it easy for myself to only be near the speaker connectors and away from the transformer...
Then of course afterward, I'll need to shut it down, and let it dissipate for a day before touching it all.
Unless you know of any ways to drain the voltage out quicker?

Thanks,
CZ

 

[spec]

I think this is possible... I'd need to get the speaker back out of the box..

I'd assemble it back just like it is in this pic:

View attachment 102274

I was doing some noodling in thought on this, and the two or one blown resistor at the bottom (where it says "Bad Resistor) - the white connector goes to the pre-amp pcb (even says it on the board), which kind
of now makes sense to me why no sub woofer output is present, but is fine for the two mains (they're going thru).

View attachment 102275
I do feel the issue is in this neighborhood.

I'll run this next test tomorrow with all the guts on the table.

And of course: I'll Bear in mind that mains voltages will be present on the circuit up to the primary of the toroid transformer (big & round) so please take care.

I'll make it easy for myself to only be near the speaker connectors and away from the transformer...
Then of course afterward, I'll need to shut it down, and let it dissipate for a day before touching it all.
Unless you know of any ways to drain the voltage out quicker?

Hi CJ,

Yes that would be good. What you heed is a completely configured system but with access to all the boards.

You are very wise to be cautious, but you will not need to wait a day before touching the circuit. I would say that, without seeing the schematic that 5 minutes would do. The golden rule is not to touch the system while the mains is plugged in. If you make measurements you normally unplug the system and connect the common lead of your multimeter to zero volts somewhere and then plug the system in and make measurements with a well insulated probe. It is also wise to power the system by a trip that disconnects the power in case of an inbalance between live and neutral currents.

I am wondering, in view of the surprising complexity of of the bass sub, if it would not be better to take it to a repair shop, or even ask a friend who has experience of repairing complex equipment.

spec

 

[chinjazz]

Hi CJ,

Yes that would be good. What you heed is a completely configured system but with access to all the boards.

You are very wise to be cautious, but you will not need to wait a day before touching the circuit. I would say that, without seeing the schematic that 5 minutes would do. The golden rule is not to touch the system while the mains is plugged in. If you make measurements you normally unplug the system and connect the common lead of your multimeter to zero volts somewhere and then plug the system in and make measurements with a well insulated probe. It is also wise to power the system by a trip that disconnects the power in case of an inbalance between live and neutral currents.

I am wondering, in view of the surprising complexity of of the bass sub, if it would not be better to take it to a repair shop, or even ask a friend who has experience of repairing complex equipment.

spec

Hi Spec,

I just woke up and checking email. You must not ever sleep ...

I get what you're saying regarding the complexity. I feel that I've gone this far, and for me to not do something at this point would be out of character for me.
I'd like to at least try replacing these parts if I knew where to get them.. Should be a cheap enough experiment.

I'm certain that at least one of them failed...

This one I don't know what it is:

These small resistors:

I'd be reasonably satisfied removing these, possibly testing them individually, buying them on-line, and once
reinstalled seeing where it gets me.

I'm currently not gainfully employed and don't have funds to bring it to a shop.

Thoughts?

Thanks,
cz

 

[spec]

Hi CJ,

I hope you didn't mind me suggesting getting help with fixing your bass sub, but what concerned me is that often you can create more havoc trying to repair complex equipment if you don't have all the test equipment and the service manuals. I have done just this. My mate, who services musical gear, tears his hair out when he gets a rig that has been previously 'serviced'.

As I have said many times before, it is a great shame that you are not just down the road, because I could then call around and advise. It is extremely difficult, as many of us have found on ETO, to do remote fault-finding.

But we will have a go and see what can be done. I will consider the next move.

About getting components, that is easy, especially as you are in the States and most components on a bass sub are liable to be standard types. DigiKey is one of the most popular component distributes with home makers. But, Mouser, Arrow, RS (Allied), Element 14 (Farnell) (Newark) are good too. There is also a slew of smaller distributors and then there are the budget retailers, ebay being the biggest, followed by Alibaba and then Amazon, I guess.

https://www.digikey.com/
https://www2.mouser.com/?gclid=CjwK...ZUejah5v8ygTisC9ahOSutP6GZ1q1isW4WhoCzI7w_wcB
https://www.arrow.com/
https://www.alliedelec.com/
https://www.newark.com/

As to sleep, I generally hit the hay around 12.30pm and sleep until 7am, if I have been active. But if not, it is 1pm, up at 4am, back to bed at 6am, sleep till 8:30am. But I also tend to fall asleep on the settee around 7pm for half an hour. On the other hand, after a few pints of Butcombe (excellent local real ale) it would be bed at 1am and oblivion until I get a dig in the ribs from the missus, some time the next morning.

Before I retired, sometimes we worked 24Hrs with no sleep, when there was a panic on.

spec

 

[chinjazz]

Hi CJ,

I hope you didn't mind me suggesting getting help with fixing your bass sub, but what concerned me is that often you can create more havoc trying to repair complex equipment if you don't have all the test equipment and the service manuals. I have done just this. My mate, who services musical gear, tears his hair out when he gets a rig that has been previously 'serviced'.

As I have said many times before, it is a great shame that you are not just down the road, because I could then call around and advise. It is extremely difficult, as many of us have found on ETO, to do remote fault finding.

But we will have a go and see what can be done. I will consider the next move.

About getting components, that is easy, especially as you are in the States and most components on a bass sub are liable to be standard types. DigiKey is one of the most popular component distributes with home makers. But, Mouser, Arrow, RS (Allied), Element 14 (Farnell) (Newark) are good too. There is also a slew of smaller distributors and then there are the budget retailers, ebay being the biggest, followed by Alibaba and then Amazon, I guess.

https://www.digikey.com/
https://www2.mouser.com/?gclid=CjwK...ZUejah5v8ygTisC9ahOSutP6GZ1q1isW4WhoCzI7w_wcB
https://www.arrow.com/
https://www.alliedelec.com/
https://www.newark.com/

As to sleep, I generally hit the hay around 12.30pm and sleep until 7am, if I have been active. But if not, it is 1pm, up at 4am, back to bed at 6am, sleep till 8:30am. But I also tend to fall asleep on the settee around 7pm for half an hour. On the other hand, after a few pints of Butcombe (excellent local real ale) it would be bed at 1am and oblivion until I get a dig in the ribs from the missus, some time the next morning.

Before I retired, sometimes we worked 24Hrs with no sleep, when there was a panic on.

spec

Hi Spec,

I completely understand your suggestion, and no worries there. It is a tough project to try remotely fixing something as complex as this,
and I can imaging what a pain in the rear it is to fix previously "serviced" units..

I do have a friend who might be able to have a look with me on it.

Thanks for the resources (links) on parts.

Here's my lack of knowledge shining thru clearly...

What is this 3 pronged black component ? I tried identifying it by number on the web, but couldn't find it:

​

Wow, you do have an interesting sleep pattern.. For me, I stay up till about 11 or 12, up at 5am, sometimes 4.
But since I've been un-employed, I'm more erratic.

Thanks!!

 

[spec]

Hi CJ,

I do have a friend who might be able to have a look with me on it.

That would be q good idea.

Thanks for the resources (links) on parts.

No probs. As I said you are in te best part of the world for components.

What is this 3 pronged black component ? I tried identifying it by number on the web, but couldn't find it.

Three terminal components are often transistors either, NBJTs, PBJTs, NMOSFETs or PMOSFETs. The most common for audio amplifiers is NPN Bipolar Transistors (NBJT) and their compliment PNP Bipolar Junction Transistors. Big manufacturers tend to get their parts directly from the manufacturers and have their own custom number marking, so it is often not possible to get a replacement, except from the equipment manufacturer, if they will cooperate- often not. But, having said that, most components are standard and if we can see the circuit diagram we can recommend a standard part, which can often be better than the original where there is a weakness in the design.

Wow, you do have an interesting sleep pattern.. For me, I stay up till about 11 or 12, up at 5am, sometimes 4.
But since I've been un-employed, I'm more erratic.

That makes sense. It is important to keep a positive outlook when you are out of work and get as much exercise as possible. I was out of work for six months once, and I know it is not much fun, being retired with a few decent pensions is a different story though. In some parts of the UK being unemployed is a way of life because of the closure of many heavy industries: coal, steel, automobile...

'Unemployment', would be a good topic for a new thread in the 'Members Lounge' on ETO. Quite a few members would be interested and would probably contributes, I suspect.

May I ask why you are out of work. Is there high unemployment in Jacksonville FL?

spec

 

[chinjazz]

No probs. As I said you are in te best part of the world for components.
Three terminal components are often transistors either, NBJTs, PBJTs, NMOSFETs or PMOSFETs. The most common for audio amplifiers is NPN Bipolar Transistors (NBJT) and their compliment PNP Bipolar Junction Transistors. Big manufacturers tend to get their parts directly from the manufacturers and have their own custom number marking, so it is often not possible to get a replacement, except from the equipment manufacturer, if they will cooperate- often not. But, having said that, most components are standard and if we can see the circuit diagram we can recommend a standard part, which can often be better than the original where there is a weakness in the design.

Hmm.. Wow, I wonder if this is tough luck on this part... No way of testing it in isolation to ensure it's bad?

May I ask why you are out of work. Is there high unemployment in Jacksonville?

Actually there's a decent economy here, but demographically speaking it's a city with roughly 1 million residents,
and the industries here are a bit more specific (financial servicing, banking, insurance, transportation/logistics), and
my preferred work is iOS app development - demand isn't so great where it's higher for web developers. Luckily,
I have an impressive history as a tech project manager that I'm starting to ignite again, but I prefer iOS dev.
Shouldn't be too much longer before I get the + money flow again.. Thanks for asking

 

[spec]

Hmm.. Wow, I wonder if this is tough luck on this part... No way of testing it in isolation to ensure it's bad?

Yes, if it is a normal component it can be tested easily. I will define.

Actually there's a decent economy here, but demographically speaking it's a city with roughly 1 million residents,
and the industries here are a bit more specific (financial servicing, banking, insurance, transportation/logistics), and
my preferred work is iOS app development - demand isn't so great where it's higher for web developers. Luckily,
I have an impressive history as a tech project manager that I'm starting to ignite again, but I prefer iOS dev.
Shouldn't be too much longer before I get the + money flow again.. Thanks for asking

No probs- I'm a nosey parker by nature. Sounds hopeful, from what you say. Ios is a fairly good area to be in. You no like Win? Or is that a dirty word.

spec

 

[spec]

About testing components, can you describe your multimeter and ideally give the model number? Or even an image so that the switches and ranges can be easily identified.

spec

 

[chinjazz]

Yes, if it is a normal component it can be tested easily. I will define.

Awesome!

No probs- I'm a nosey parker by nature. Sounds hopeful, from what you say. Ios is a fairly good area to be in. You no like Win? Or is that a dirty word.

spec

I like Win dev but it's not that exciting - my last gig I did strictly that (a .net WPF - XAML thick client application), kinda cool stuff, but most companies are looking
for .net web apps.

 

[chinjazz]

I like Win dev but it's not that exciting - my last gig I did strictly that (a .net WPF - XAML thick client application), kinda cool stuff, but most companies are looking
for .net web apps.

Sure thing....

I've got two (but use the Innova 3320 mostly):

Here's the on-line manual:

**broken link removed**

 

[chinjazz]

Update: I took the Transistor and the two questionable resistors off.
On YouTube, Learned how to identify and test the Transistor, and it was in fact a PNP Bipolar Junction Transistor, and it was bad.

Couldn't find a replacement, and I'm quite certain I won't be able to get the part from KRK.. SOL as they say.

I'm either going to bring it into to a service center that's authorized depending on the cost, or buy the whole back panel for $180+ from compass (once I get $$)...

Oh well.... I do appreciate ALL of your help on this Spec!

Thanks, CZ...

 

[spec]

Hi CJ,

Update: I took the Transistor and the two questionable resistors off.
On YouTube, Learned how to identify and test the Transistor, and it was in fact a PNP Bipolar Junction Transistor, and it was bad.

Couldn't find a replacement, and I'm quite certain I won't be able to get the part from KRK.. SOL as they say.

I'm either going to bring it into to a service center that's authorized depending on the cost, or buy the whole back panel for $180+ from compass (once I get $$)...

Oh well.... I do appreciate ALL of your help on this Spec!

Thanks, CZ...

The service center would be the best approach. You can not be sure that replacing one board would cure the fault.

Good luck.

spec

 

[chinjazz]

Hi CJ,



The service center would be the best approach. You can not be sure that replacing one board would cure the fault.

Good luck.

spec

Yes, this is true: "You can not be sure that replacing one board would cure the fault".

Thanks!

 

[GromTag]

:Hello: some scattered information, hope somewhat helpful.
The blue resistor (if that is a dark blue stripe on the light blue housing) is 68 Ohm. The other Green a 10 Ohm unknown tolerance. If the stripe after the black is a metallic the tolerance, Gold 5%. for other resistors, Brown 1%, Red 2%, a leap to Silver at 10%. The resistors do look corroded. The transistor (three lead IC) C3206, or 2SC3206 appears to be KEK Korean Electronics. However data listed as an NPN? transistors can show odd results when damaged. However a solution for outer trace Ic's such as 3 pin transistors is to try to follow the Emitter track to either a positive or a lead to common. P channel would usually be Emitter to Positive voltage source, the N channel Emitter to common ground. This can be used under typical situations to identify the type on an existing legible pc board. There are however in some circumstances when transistors are used in many other ways. The transistor (if my results are correct) is a Triple Diffused PCT type, meaning its manufacturing method. Features are 150 Volt DC @ 50mA. a low power switch. So more than likely if the part number matches is a sinking transistor switch configuration, turning on something elsewhere. Cases such as near that ribbon connector? the other end board may require that transistor to act as a switch on to function from the board it's on. Or it could be just for that board, the tracts are a bit tough to see clearly as if that transistors leads connect to that ribbon connector or turn back to that board. as for the IN4148 Schotty diode they are easy to burst when reverse voltage breakdown occurs due to over current or reverse high voltage spike that can result in a crack or complete small firecracker effect.