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zeron

Klipsch SW-12 subwoofer noise (1993/1994)

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Hello,

 

I've had an SW-12 since 1993/1994.

 

It had been working very well until about two weeks ago.

 

About two weeks ago, it started making two kinds of noises after it gets warmed up for a while, like 6 - 35 minutes. One kind of noise is static-like and the other kind is what I'd call crackling kind (could be the sound of clipping).

 

These noises come on whether any source is connected or not. Until these noises come up, the subwoofer appears to work as good as before. Once these noises start, none of the controls (LEVEL, PHASE, and LOW PASS) has any aural effects on the noises as far as I can tell.


I've plugged the power cord of the unit to many different wall outlets in my 2-story house and also with or without my computers, cable modem, router, etc. ON, and the problem shows up anywhere. So, I'm leaning towards ruling out things like ground loop or interference from Wii-fi, etc. as the cause of the problem.


Even after the noises show up, the source material keeps getting reproduced as usual.


I suspect the problem has something to do with overheating of the amplifier because they don't show up immediately after I turn the unit on. Also, I found one area of the top plate of the plastic cover that covers the amplifier has a sign of getting soft before, but I have no idea when it happened.


I have connected the speaker leads inside to a regular speaker and the noises came on, so I'm ruling out the problem lies with the subwoofer's speaker unit.


I have cleaned the pots for the controls fairly well, too, so they're probably not causing this problem either.


I'm now concentrating on the amplifier. As a starter, I downloaded a service manual of SW-12 and SW-15. It's here:


http://www.audiolabga.com/pdf/SW12-15 I.pdf


 

Pages 15-17 are the schematic of SW-12.


The top portion of Page 16 (Sheet 2 of the schematic) is the part I'm concentrating on [labeled DRIVER CKT filter driver bd.] now because the location of the cluster of 4 transistors (Q7, 8, 9, and 10) coincides with the previously softened area on the amplifier's plastic cover and also the area on the circuit board these four transistors lie on is not burned badly but dark brown. (Each of these transistors has its own little heatsink, so they are probably known to get hot, but maybe with my unit, they may be getting too hot to affect the performance of other components in the amplifier.)


Now, I'm completely clueless when it comes to electronics. I'm hoping that someone here can help me with questions I have about the schematic and electronics in general.


Tonight, I removed the amplifier and measured about a dozen resistors' values with the unit turned off without any source signal being fed to the amplifer. Since my multimeter can't test capacitors, I'm not going to mess with capacitors now.


Obviously, I don't want to remove any components from the circuit board to take their measurements if I can avoid.


As far as I could tell, there were no apparently damaged components or suspicious solder joints.


Four resistors caught my attention, though:


One is R45 1M. It's first resistor on the DRIVER CKT (on the left on the schematic). When I take a reading, the value is only about 109K.


Here is my first set of questions:

 

1. Do I need to remove at least one end of R45 to get an accurate reading?

2. If it's faulty and I install a good one, would it make any noticeable difference in the circuit?


Two other resistors which give different values than the specs' are R74 and R73. Their values should be 2.7K ohms according to the schematic and the parts list in the service manual. My meter reads about 1.42K ohms.


Here's my second set of questions:


3. Do I need to remove at least one end of R74 and R73 to get their accurate readings?

4. If they're faulty and I install good ones, would they make any noticeable difference in the circuit?


 

And here's my final question for tonight:

 

5. If you were tackling this problem, where would you start?


 

Thank you in advance for reading this post and possibly offer some answers/advice/suggestions.


Happy Listening!

 

-------------------------------------------------------------

 

Additional comment:

 

The main heatsink on the back of the amplifier never gets hot. It remain just mildly warm. On the other hand, the small heatsinks on the four transistors on DRIVER CKT get too hot to touch.

Edited by zeron
corrected errors due to dropped/extra words, etc.; also added "Additional comment" at the bottom.

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Take the thing apart so the circuit board is exposed, and connect source and speaker to it. Oh, look for burnt parts and isolate that, and I guess you've eliminated those.

Wait till the noises come. Spray various parts with cold air from those compressed air cans for dusting starting with parts bolted to heat sinks.

Cool.

Srinath.

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On 1/15/2017 at 11:45 PM, Srinath said:

Take the thing apart so the circuit board is exposed, and connect source and speaker to it. Oh, look for burnt parts and isolate that, and I guess you've eliminated those.

Wait till the noises come. Spray various parts with cold air from those compressed air cans for dusting starting with parts bolted to heat sinks.

Cool.

Srinath.

 

Thank you for your suggestions, Srinath.

 

1. I see no apparent burnt parts or bad solder joints on the top circuit board. I can't check well how the second circuit board and components on/below it are, but as far as I can see, they look all right.

 

2, The four things on the front panel [The LED and the three pots for LEVEL, PHASE, and LOW PASS] are connected to the amplifier through two connectors. I've tested the amplifier with the driver attached but without connecting any of the above to the amplifier. I have confirmed that the noises come on this way..

 

3. I have not been able to pinpoint which component or components get hot to cause the noises with the cold air method so far.

 

4. Thinking that lowering the inside temperature of the amplifier covered with the black plastic cover without any vent holes might keep everything in the amplifier cool enough to operate without making any abnormal noises, I made some holes on the plastic case. I put everything back together except two foam sheets (to help air movements inside the subwoofer enclosure easier) to test with music. In about 20 minutes the noises came back. It seemed the holes on the plastic case didn't change anything.

 

5. I disassembled the subwoofer again to check/test further.

 

6. I turned on the amplifier (without any source signal) with the plastic cover completely off more than two and a half hours ago. I have not detected any noise (except very faint hum that is expected) so far.

 

 

Attached pictures:

 

SW12_012: The amplifier with the cover off. The amplifier is resting on its heatsink. The gold dots on the plastic cover are makings for drilling.

 

SW12_013: The darkened area under the cluster of transistors I mentioned in the opening post.

 

SW12_015: The amplifier resting on the top of the subwoofer enclosure with its plastic cover completely off.

 

SW12_016: Closeup of the amplifier and its cover. You can see on the top panel of the cover, the softened (deformed) area due to heat that I mentioned in the opening post.

 

----------------------------------------------------

 

I'll test with source signal next to see if the noises come back in this setup.

 

 

Any comments, questions, and suggestions are appreciated.

 

 

 

 

 

SW12_012.JPG

SW12_burned013.JPG

SW12_015.JPG

SW12_016.JPG

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"I'll test with source signal next to see if the noises come back in this setup."

 

I turned on the amplifier in this setup at 4:57 a.m.

 

I left it on until 8:16 a.m. I had heard no unusual noise during this period, which was well over 3 hours.

 

I turned off the amplifier to connect the control pots and LED to the amplifier and turned the amplifier on immediately and started playing music through my LaseDisc player and AVR for about 25 minutes. I heard no unusual noise either. I turned off the amplifier.

 

This test result suggests that I could try one of the following:

 

1. Drill more holes on the plastic cover.

 

2. Install the amplifier on the subwoofer enclosure without the plastic cover.

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3 minutes ago, zeron said:

This test result suggests that I could try one of the following:

 

1. Drill more holes on the plastic cover.

 

2. Install the amplifier on the subwoofer enclosure without the plastic cover.

Seems you're band aiding it.  The amp ran for a long time in the old configuration.  Running it open air may work for now but I believe you're delaying the inevitable.

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I had a little progress yesterday evening.

 

The noises definitely changed. I could say the two kinds of noises I had been having, static kind and crackling kind, disappeared completely, but a more regular kind of noise started coming on, still only after the amplifier is warming up. This noise is like that of water dripping from a faucet with drops about 5~8 seconds apart.

 

What I did yesterday evening was re-soldering all solder joints on the circuit boards that didn't look quite robust (not plump, wet-looking, etc.). One notable group of solder joints that I touched up was directly beneath a variable resistor (R131 in the CURRENT SENSE section).

 

During the test I performed last night, I noticed that 6 of 12 ceramic resistors in the POWER AMP section getting extremely hot. One of them was loose during the test. During the test, I thought I didn't solder its leads to the circuit board well, but when I turned off the amplifier, it became solidly anchored to the circuit board within 10 seconds or so. It was just getting hot enough to melt solder. I also re-soldered ends of about 10 wires running between the circuit boards.

 

Any idea what could be causing this new kind of noise?

Edited by zeron

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Too bad we don't have a subwoofer plate amplifier repairman on the forum, he could make a mint repairing all the amplifiers that go bad on these subwoofers.

 

The inside if a subwoofer is a harsh environment for any electronic device.

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31 minutes ago, jason str said:

Too bad we don't have a subwoofer plate amplifier repairman on the forum, he could make a mint repairing all the amplifiers that go bad on these subwoofers.

 

I've said the exact same thing in the past.

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7 hours ago, zeron said:

During the test I performed last night, I noticed that 6 of 12 ceramic resistors in the POWER AMP section getting extremely hot. One of them was loose during the test. During the test, I thought I didn't solder its leads to the circuit board well, but when I turned off the amplifier, it became solidly anchored to the circuit board within 10 seconds or so. It was just getting hot enough to melt solder. I also re-soldered ends of about 10 wires running between the circuit boards.

 

A breakthrough!

 

The amplifier went completely dead while I was testing it. The resistor that was getting really hot (750 ohm 5W ceramic type; R88 or R90 on the schematic) used to measure about 750 ohms. It seems completely open now.

 

Obviously, I'll have to replace this open resistor. The question is whether the new replacement resistor will burn itself up, too?

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6 minutes ago, zeron said:

The question is whether the new replacement resistor will burn itself up, too?

I would think so but resistors are cheap.  I would also think it's a transistor but couldn't say for sure.

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On 1/26/2017 at 6:31 AM, zeron said:

What I did yesterday evening was re-soldering all solder joints on the circuit boards that didn't look quite robust (not plump, wet-looking, etc.). One notable group of solder joints that I touched up was directly beneath a variable resistor (R131 in the CURRENT SENSE section).

 

During the test I performed last night, I noticed that 6 of 12 ceramic resistors in the POWER AMP section getting extremely hot. One of them was loose during the test. During the test, I thought I didn't solder its leads to the circuit board well, but when I turned off the amplifier, it became solidly anchored to the circuit board within 10 seconds or so. It was just getting hot enough to melt solder. I also re-soldered ends of about 10 wires running between the circuit boards.

 

I think my re-soldering job was bad. I found one solder-joint was over two conductive tracks of one PCB in the amplifier causing, a short. This explains why one resistor (R88) read got so hot it came loose when the amplifier was on. After turning off the amplifier I took the readings of all 12 ceramic resistors. R88 and R90 read funny. R88 read 423 ohm and R90 0 ohm while they were still on the PCB. Yes, it seems cooling down restored R88's resistance to some degree Off the PCB, R88 and R90 read 428 and 756 ohm, respectively. They are both supposed to read 750 ohm +/- 5%, so R88 must be definitely replaced, but R90 being 0 ohm (in circuit) and resistance between two plates where the two leads of R90 were attached to being 0 after R90 was removed worried me for two days because it could mean that a transistor/transistors connected to it electronically may have been shorted. However, after testing all 12 transistors in the POWER AMP section of the amplifier, I concluded that NONE of them was shorted. I found the cause for the strange reading on R90 last night by tracing relevant conductive tracks of the PCB. The two conductive tracks it was attached to was shorted by one solder joint I touched up before the noises changed. I fixed this problem already.

 

(By the way, both R88 and R90 are bulged and cracked on one side. So, I'm going to replace R90 as well.)

 

The replacement resistors should arrive by this Friday (2/3/17), so hopefully, I can test the subwoofer this weekend. I have a rather strong feeling that I had fixed the problem causing the original noises before I introduced this new problem. I think it was bad connection between R131's three leads and the PCB's conductive tracks, which I had corrected already.

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On 1/30/2017 at 11:38 AM, zeron said:

The replacement resistors should arrive by this Friday (2/3/17), so hopefully, I can test the subwoofer this weekend. I have a rather strong feeling that I had fixed the problem causing the original noises before I introduced this new problem. I think it was bad connection between R131's three leads and the PCB's conductive tracks, which I had corrected already.

 

I replaced the old R88 with a new one. I put the R90 back in its original spot.

 

The amplifier works now, but one noise came back. It's the crackling kind. The static-like noise seems to have disappeared.

 

Basically, I spent about a week restoring the amplifier to its previous (bad) state. I didn't destroy it with my bad soldering job, though.

 

==============================================

Update (4:12 p.m. Pacific Time):

 

I listened  to music for about 90 minuets with my subwoofer ON. I heard no noise. I left the cover off, so, I haven't proven I fixed the amplifier. The noise I heard earlier may have been due to the fact one resister is not soldered to a PCB yet.

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Update:

 

It appears that I'll have to change R87, R88, R89, and R90 to 7W 750 ohm or 5W with resistance higher than 750 ohm. The service manual's part list specifies that they be  5W 1.5K ohm while the schematic indicates 5W 750 ohm. The originals are all 5W 750 ohm, and apparently they've been getting very hot, maybe too hot to be stable and functioning properly.

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Sorry to say I rarely come on the forum, but did today because of frustration with one of my OLD subwoofers.  I have two sw10s running off of the "preamp out" section of my amp, one for each channel to supplement my set of Quartets (yes some of us have Chorus and Forte's little brother.)  One of the subs I bought new (works fine) the other, bought used,  performed OK when I got it, although it seemed a little down on volume production compared to "mine".

 

THEN THE SAME THING THAT THE OP DESCRIBED started to happen.  Exactactly.  Six to ??? minutes in, nasty crackly.  I've been around stereo stuff and guitar amps most of my life, and just assumed I had a "blown speaker", oddly, because I had never had one be "blown".  After telling myself the music was just to bassy, and needed to be turned down, I just couldn't listen anymore.  Each time I thought it had gone away, but faithfully, after warmup, there was that nasty crackling again.

 

I took the driver out and packed it up to a guy I think I read about on this form, Nevisonics.  He emailed me saying that there was absolutely nothing wrong with it!!  What a bummer, I wasted $$$ on his time and shipping both ways!!  I find I started listening to my system less and less (partly as I was getting more back into playing live music and practicing time soaked up what had been listening time).  I started looking on Ebay, saw several units, and even an amp, but shipping made them cost prohibitive, and, who could say if that unit might not have the same issue.  Pooooh, I love my twin, stereo, highly musical subs, both sonically and cosmetically.  Then a guy was selling one without the amp, saying it would be perfect for driving with some other amp.  DUUUUUuuuuuuuHHHHhhhhh--Gees, I have two older integrated amps sitting around,  hooked everything up today,  It has a GrE so I can zero all frequencies except the last two levels or so.  I'll test it out tomorrow when wife is out of the house.

 

But, like the OP, I came on here wondering--does no one rebuild them??  I would think this issue would have surfaced many times and the cause found, and someone like the Mr. Crites I read about here with a fix---- send it in , bing, get the amp back.  Nothing in that way of advice seemed to be offered the OP.  Someone must know.

 

Anyway, I don't have the drawings, and wouldn't know what to do if I did.  I can't solder for #@%$#@.  Guitars, saxes, cars, I know it all, but not my stereo stuff.  But here's a thought for the OP and others,  if this is happening to an SW12 AND an SW10, it must be because of something they have in COMMON!!  No? 

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13 hours ago, moxie50 said:

But, like the OP, I came on here wondering--does no one rebuild them??  I would think this issue would have surfaced many times and the cause found, and someone like the Mr. Crites I read about here with a fix---- send it in , bing, get the amp back.  Nothing in that way of advice seemed to be offered the OP.  Someone must know.

Google Edwards Electronics.

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1 hour ago, moxie50 said:

Thanks for the tip, I'll call them.  Sw10 is not on their specific price list, but Rw10 is.

I haven't personally used them but several members here have.  I haven't read a bad report yet.

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