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ngen33r

RSW-10 / RSW-12 / RSW-15 REPAIR BLOG

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Hello All

 

I have been repairing Klipsch subwoofer amps for about 15 years as a hobby. I have decided to start blogging my repairs and eventually do videos of each one. This thread is intended to be a blog and a resource for information. I will try to answer repair questions as best I can. Comments and tips are also welcome, If you do not have the experience or the tools, PLEASE do not attempt any of these repairs. You will only end up damaging the board and it will end up costing more for a tech to repair the damage. If you do not have a high quality vacuum desoldering station (Hakko or Weller) and a current limited mains supply, you should not be working on these amps. These subwoofers do not have any user serviceable parts inside. If you open up the sub or attempt any repair you see in this thread, you are doing so at your own risk!!!

 

Wayne

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Posted (edited)

RSW-10 PLATE SERIAL ???

 

First up we have a RSW-10 and this one already is a challenge, because someone was already inside and changed parts. I have 2 burnt resistors that look to be replaced and might not be the correct value. R44 and R45 on the amp board. I also see that 3 fets were replaced. I need to confirm that Q7 should be an IRF640 and not a IRF530. The amp board is 650027 and it appears that SVS used this same amp in the 20-39PC. Oddly enough the Infinity IL60 uses the same amp board so I should be able to get a good parts reference from that. More to come tomorrow, I'm tired.

 

Update:1/18/20

 

I replaced the fets and have the resistors on order. The resistors are .1ohm 2W Wire Wound

 

ADJUST BIAS PROCEDURE
(Mandatory when any output MOSFET transistors Q3,4,7,8 are replaced)
1. Amplifier should be unplugged and OFF.
2. Remove Amp assembly from cabinet; remove rear plastic cover if present. All wires exiting
the cover can remain connected unless they will prevent you from removing the amplifier or
accessing potentiometers on the Linear board PCB in the following steps.
3. Locate the Linear board assembly (PCB with the output transistors)
4. Adjust R11 and R27 fully Counter Clockwise. See diagram below.
5. Apply 120 VAC power to unit, Turn power switch ON.
6. Verify LED illuminates on the front gain control dial unless you have disconnected the plug.
7. Connect voltmeter set to DC millivolt range to twin pins on terminal J7, on Linear board
8. Verify initial voltage is less then 0.1 mV.
9. Adjust R11 Clockwise until voltmeter reads 0.3 mV + the initial current from step #8.
10. Adjust R27 Clockwise until voltmeter now reads 0.6 mV + the initial current from step #8.
11. Turn amplifier OFF. Disconnect AC power to unit.
12. Remove voltmeter from terminal J7.
13. Replace cover (if present), wires if disconnected, and replace amplifier back into cabinet.

 

 

 

 

20200106_012541.jpg

Edited by ngen33r

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I posted my repair success on my RSW15 on another post.

But just some funny things you see on previous repair attempts


When finally re assembling the indigo bash board I was missing 6 screws. I just assumed after 2 years I had lost them. Then I took a closer look at the picture I took originally when I disassembled it. There where NO screws! The pcb is floating above the mounting tabs!  The guy had put screws thru the TO220 mounting holes systematically shorting every power FET and Diode!  LOL no wonder it didnt work!   Egg on my face for not catching this originally... oops!  

 

1634945879_SWR15SubAmpshortingscrews_LI.thumb.jpg.e54a40483a3670b70f0b0cb4f7ace369.jpg

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Yea OOPS but like Forest said "_ _it happens":)

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Plate?

 

This is one that separates the men from the boys. This amp came to me a complete mess. It successfully achieved meltdown. The inductor on the secondary power supply overheated and was destroyed. I took some measurements, ordered the special LITZ wire and 3D printed a new bobbin for the coil. I then vacuum potted the coil with thinned polyurethane and let it air dry for a week. I still need to do more repairs on the amp, It has shorted fets and outputs and all sorts of other issues, but here is a teaser for this one.

 

One thing I learned, is definitely to tin the leads before starting the winding and before potting. It was not easy at all to clean them as they wicked up the poly.

 

 

20200104_154856.jpg

20200307_115136.jpg

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5 hours ago, ngen33r said:

Plate?

 

This is one that separates the men from the boys. This amp came to me a complete mess. It successfully achieved meltdown. The inductor on the secondary power supply overheated and was destroyed. I took some measurements, ordered the special LITZ wire and 3D printed a new bobbin for the coil. I then vacuum potted the coil with thinned polyurethane and let it air dry for a week. I still need to do more repairs on the amp, It has shorted fets and outputs and all sorts of other issues, but here is a teaser for this one.

 

One thing I learned, is definitely to tin the leads before starting the winding and before potting. It was not easy at all to clean them as they wicked up the poly.

 

 

 

 

Very nice. .what inductor was that? The L302?  how did you deduce the inductace value? Schematic? Interesting that yours was melted too.  Mine also.. purchased used/defective.  Where an fets or diodes blown also? 

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On 3/13/2020 at 10:15 PM, efzauner said:

Very nice. .what inductor was that? The L302?  how did you deduce the inductace value? Schematic? Interesting that yours was melted too.  Mine also.. purchased used/defective.  Where an fets or diodes blown also? 

 

L302. The inductance is 150uH air core. Shorted fets and outputs caused this. The power supply puts out enough power between current limiting shutdown to heat the coil if left plugged in. So if your unit wont come on, don't leave it plugged in. The wire to wind this is stupid expensive.

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On 3/16/2020 at 10:51 AM, ngen33r said:

 

L302. The inductance is 150uH air core. Shorted fets and outputs caused this. The power supply puts out enough power between current limiting shutdown to heat the coil if left plugged in. So if your unit wont come on, don't leave it plugged in. The wire to wind this is stupid expensive.

ok thanks just confirming my repair as well.  I used solid wire. worked well enough if not perfect. Measured on HP 4800A Vector Impedance meter! 

What wire gauge did you use? size of coil # of turns etc. Just in case I want to redo mine using litz 

 

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You sound like the competition, I should not be giving out these trade secrets. HAHHAH

The wire I used is 80/38 LITZ. 

Coil ID 16mm

Coil Height 22mm

110 Turns

 

It is as close to factory spec as I could get not that it needs to be. 110 turns of 18awg solid would be painful on the thumbs if wound tight.

 

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Posted (edited)

wrt to rewinding a coil.....

 

FYI, I am not a design engineer, but do have an engineering degree with a concentration in computer architecture.

 

First off, there is an important reason for using Litz wire in the windings of inductors used at high (i.e. radio) frequencies which would include switching power supplies. It has to do with what's called "skin effect" and "proximity losses" (Litz Wire Info (on Wiki)). It means that the effective resistance of the wire is increased (which can reduce the "q factor") which can cause all sorts of other problems, the least of which is reduced efficiency of the circuit it's in. Not using Litz wire where it was used in an original design is setting things up for imminent (and possibly, catastrophic) failure again soon.

 

Having said that, while Litz wire can be expensive depending on the guage used, there are articles and websites that discuss creating your own Litz wire out of fairly normal enameled copper wire. Invest some time and save a few bucks...and do it right :)

 

  Good luck and cheers......

Edited by stepher

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I am not sure in this application that it matters. The switching frequency is under 1MHz and 99% of the other Bash amps use solid copper in the class H buck supply. I would expect maybe some increase in harmonic distortion or some extra ripple on the filter cap but not catastrophic failure. Either way I went with OEM specs.

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Posted (edited)
8 hours ago, ngen33r said:

I am not sure in this application that it matters. The switching frequency is under 1MHz and 99% of the other Bash amps use solid copper in the class H buck supply. I would expect maybe some increase in harmonic distortion or some extra ripple on the filter cap but not catastrophic failure. Either way I went with OEM specs.

 

Maybe. Maybe not. I read that you went with OEM specs, and that was the right thing to do. I wanted to make sure others don't get the idea that substituting without fully understanding how something is used in a circuit design can lead to serious problems.

 

SMPSs (Switch Mode Power Supplies) typically output DC for the amp, and that may sound straightforward. Getting to that point is not. An SMPS is a complex design. It takes AC (110 or 220) from the wall, converts it to high voltage DC, turns it back to AC (really more oscillating DC/digital), reduces it, rectifies and then filters before it goes to the load (the amp, in this case). Oh, and don't forget the regulation part, which is a feedback circuit to the input to maintain output voltage(s) with both line and load changes, and more.

 

If one is not well versed in the design or, a least, the circuit operation of an SMPS, messing around with anything in the circuits can cause catastrophic problems. As @efzauner stated abt measuring inductance, that is only part of the equation. The wire resistance (due to skin effect) also plays an important role and failure to consider that can have a serious impact on circuit performance. You mentioned harmonic distortion or extra ripple. True, except that the ripple can be enuf to impact sound quality and/or tear the circuit apart. And distortion can come in the form of clipping due to the power supply not being fully functional.

 

You're right. It may not matter under certain circumstances. At low volumes...hopefully not. However, because of the typical power of a subwoofer amp (50W and up) and the frequency range in which the subwoofer operates, it may matter a lot.

 

Having said all that, it's possible that the Litz wire was a cost consideration. If a number of other coils/inductors/transformers in the p/s design used Litz wire, then using it in the coil referenced here may have been only an incremental cost, as opposed to having to order a small quantity of solid copper wire at a higher price, and using copper wire may not make a noticeable difference. On the other hand, would you want to have to face a customer who returned a unit you repaired that worked for only a short time and then went ballistic again. There goes whatever profit you might have made the first time (I used to repair TVs, stereos, etal when I was in high school and college).

 

Whatever choice is made, be ready to deal with possible consequences.

 

  Cheers....

Edited by stepher

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@stepher

   All good points.  When I fixed mine, the previous repair already had attempted to make an inductor out of solid wire. I did not know that the original part was made out of litz.   Do you know for sure that the switching frequency is 1 MHz?   I did not measure it.  Could guestimate from the RC of the PWM circuit... 

 

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Posted (edited)
On 3/18/2020 at 5:50 PM, efzauner said:

@stepher

   All good points.  When I fixed mine, the previous repair already had attempted to make an inductor out of solid wire. I did not know that the original part was made out of litz.   Do you know for sure that the switching frequency is 1 MHz?   I did not measure it.  Could guestimate from the RC of the PWM circuit... 

 

 

UPDATE (3/19/20)

 

Wanted to add a link I just found on Quora (how timely :)  It's goes to a paper from Dartmouth that discusses using uninsulated stranded wire to create Litz wire. This could be cheaper and much easier than braiding together separate single-strand wires to do this. There's more than a bit of math in the paper that might not be of much interest to you, but some of the narrative may offer you some really good insight if you are a "roll-your-own" kind-of technician.

 

To quote the 1st paragraph of the conclusion:

 

"Stranded wire can be a useful low-cost alternative to high-cost litz wire. Both the cost of insulating individual strands, and the cost of terminating the litz wire can be avoided or decreased."

 

...and here's the link:   https://engineering.dartmouth.edu/inductor/papers/stranded.pdf

 

I don't have a schematic and am not familiar with this particular product (I own a KSW-150 which has a linear p/s...much easier to work on :)  There are various forms of SMPS, one which you mention: PWM. There are other methods, as well. In fact, PWM can look like a variable frequency implementation. Current IC technology easily allows SMPS to hit well beyond 1 MHz (some go to 6MHz and beyond).

 

The best suggestion is to use a frequency counter. Use care when setting it up both for voltage (which could blow out the front end of the counter) and trigger levels (since PWM signals can sometimes appear a bit strange).

 

Also, if you want to "roll your own", there are websites and YouTube vids that can show you how to take insulated single strand copper wire and braid it so it will work as Litz wire.

 

Here's a few to get you started....Cheers....

 

https://en.wikipedia.org/wiki/Litz_wire

 

 

 

 

 

 

 

 

Edited by stepher
Additional info w/link

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Hello first time on this forum, I have a RSW 15 that has recently stopped working properly. I am by no means a technical person and don't intend on soldering anything but if given an idea I can at least pass on the info or maybe it's just a part swap. 

 Anyway the sub stopped turning on so I took a few things apart and was able to get it to turn on ONLY after unplugging the connector in the following picture and only when unplugged and plugged back in on the amp end not the other end where the RCA plugs in. I tried swapping the cord ends to the same effect. The sub works fine once powered up. But as soon as the sub powers off it will not power up again unless this connector is taken out and in again. I can't see any physical damage to the connector or where it plugs in.

thanks for any help 

sub1.jpg

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Sounds like the amp needs a recap and possible some other service.

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On 4/4/2020 at 1:36 PM, rgp6373 said:

Hello first time on this forum, I have a RSW 15 that has recently stopped working properly. I am by no means a technical person and don't intend on soldering anything but if given an idea I can at least pass on the info or maybe it's just a part swap. 

 Anyway the sub stopped turning on so I took a few things apart and was able to get it to turn on ONLY after unplugging the connector in the following picture and only when unplugged and plugged back in on the amp end not the other end where the RCA plugs in. I tried swapping the cord ends to the same effect. The sub works fine once powered up. But as soon as the sub powers off it will not power up again unless this connector is taken out and in again. I can't see any physical damage to the connector or where it plugs in.

thanks for any help 

 

 

It could be old caps as @ngen33r stated. If the system has auto-turn on (using audio from the amp, which many subs have), if the audio detect circuit has gone haywire (bad caps, transistor issues, etc.), it may behave "squirrelly".  Also take a close look at the solder connections at, and around, the connector. It may be that when the connector is plugged in, a good solder joint becomes really cold. I had this happen on my KSW-150 (and a Sony 5.1 receiver). Over time, heat can bring out the worst in a perfectly good solder joint. On the Sony it was the output transistors and must have been due to heat. On the sub, first it was a "scritching" noise which turned out to be in the low-level amp section (thought the spkr itself had blown a voice coil :( And then it was a hum which was a cold solder joint on the linear p/s filter caps.

 

Often the shortest distance between 2 points is not a straight line. :(

 

Cheers....

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