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post #1 of 16 Old 08-16-2012, 07:32 AM - Thread Starter
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Hey all,

I have a JBL Venue Sub12 with a bad amp. It powers up just fine but after about 10 minutes of being on or getting a signal, it starts poping. I took the amp out and noticed some black spots on the back of the amp board. I'm wondering if replacing the compacitors where the black spots are will fix the issue. There is a guy on ebay that will replace the amp for $140, but that seems pretty expensive if its just a couple of bad transistors.

Here are some pictures of the board.







Any idea on how I can figure out what type or model of compacitors that are?



thanks,

Jason
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post #2 of 16 Old 08-16-2012, 03:25 PM
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Well it looks as those Resistors are Getting HOT.. I dont think the Resistors are at fault it could be before that in line where the problem lies..The Blue things under those Resistors they are Capacitors..

I would just replace the amp for 140Bucks.. I would not reccomend poking around in there..

I just fixed my Subwoofer amp but did NOT have anything heating up it was just a simple Voltage regualtor problem.. Yours however seems a little more in depth..

140 Bucks for a new amp seems reasonable it would probally cost more to get it repaired then to just buy the new one..

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post #3 of 16 Old 08-16-2012, 06:25 PM
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If changing capacitors is something you can do and its easy to get them, why not, the questions is, is it the capacitors ? You could try seaching for defective capacitors, sometimes they would expand at the top, so if a capacitor with a swollen top, its a candidate for replacement. Who knows you might get lucky
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post #4 of 16 Old 08-16-2012, 06:42 PM - Thread Starter
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I'm going to remove them and see if I can find some replacements. I have done things like this in the past with no issues. Wish me luck.
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post #5 of 16 Old 12-28-2013, 11:34 AM
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Had the EXACT same problem.

Go to digikey.com and purchas a 5W 1.2kOhm resistor to replace the R9 resistor and a 3W 1.2kOhm resistor to replace the R6 resistor. I know this seems counter intuitive given the sizes of these fried resistors but I guarantee you these are the correct wattages. I have replaced both of mine in this fashion. NO MORE POPPING!!! Functioning properly now with no issues for nearly 3 weeks. Cost me a total of $5.35 since I already had a soldering iron, solder, and flux. The cost was solely for the replacement resistors and majorly shipping of these tiny parts! All in all way less than paying $140 for a new amp or entirely new sub. If you have the need I will post pics of the old board resistors and the replaced resistors. However, if you do not need these I'd prefer not to pull the amp back out of the unit. 

 

Hope this helps y'all save some bucks$$$!!!

 

Your home economically-conscious friend,

 

Hlmartin22

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post #6 of 16 Old 10-11-2014, 08:07 AM
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I realize this post is almost a year old, but I'm hoping to get some clarification from the previous post from possibly or Hlmartin22 or somebody else. I have the same issue with my JBL Sub12, and the board around my R6 and R9 resistors is definitely discolored. However, the service manual states that the R6 is 5W and the R9 is 3W. Does anyone know if the previous poster is suggesting to swap the resistor wattages, or is that a typo?
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post #7 of 16 Old 10-12-2014, 10:23 AM
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Follow up

Hi and thanks for your inquiry to my post. My best answer for you is that the resistor wattages I posted are not typos. I had the same issue when reviewing the user manual for the sub. I replaced the resistors according to the hardware that was originally in place on my amp. So either the resistors were installed incorrectly at the factory or the user manual was wrong. After labeling and removing the actual faulty resistors I looked up the wattages on the physical pieces and they were 5W on the R9 and 3W on the R6. My sub functioned flawlessly for 6 or 7 months after this fix. However, now I am experiencing new symptoms of hopefully a different issue. The sub is now making sounds that I can only assume has something to do with variable voltages being delivered to the driver (maybe I have some bad caps now). The best I can describe the noise is the sound a vacuum makes as you shove the hose against a carpet... like an inverted thump. Anyways, when I get the time to pull the sucker apart again I will repost to this thread, optimistically, with a resolution to the new problems. At the very least you should avoid spending $140 bucks for a new amp. If you have that kinda dough to attempt to fix faulty hardware, buying the exact same model (which obviously has flaws from the factory) is idiotic. Why people post to forums with "just buy a new one" is beyond me. Hope this helps and good luck!
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post #8 of 16 Old 11-03-2014, 11:04 AM
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Solving additional problems

Finally pulled the amp back out of the sub to check my new issues. As I suspected, the new problem with the sound was a bad cap. The problem capacitor was C72. This is a 6.8 microfarad 100V non-polar electrolytic cap. As seen in the pics, the cap is swollen and faulty. Will be repairing this when my replacement cap is delivered (hopefully today) and then I'll put it all back together to make sure this is the sole cause of the problem. I expect it is the only issue now. With any luck this will be the last time I have to fix the amp for a few years.
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post #9 of 16 Old 02-06-2015, 08:53 AM
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Martin!

To hlnmartin!!! I tried msg'ing you but I don't have those privileges.

Hey man! I saw your post about fixing your JBL VENUE SUB12. Mine has worked great for years and then awhile back, if it's on for more than 2 hours, just starts popping and I have to turn it off. I see that you replaced 2 resistors and it's fixed? I contacted a guy on EBAY who said he has to replace capacitors to fix the problem. Did you JUST do the resistors and it worked? Or did you have to do capacitors too? Also, did you have the same problem as me? Sorry for the jumbled message, I'm running to work!

Thanks in advance,
Adam

Quote:
Originally Posted by hlmartin22 View Post
Had the EXACT same problem.
Go to digikey.com and purchas a 5W 1.2kOhm resistor to replace the R9 resistor and a 3W 1.2kOhm resistor to replace the R6 resistor. I know this seems counter intuitive given the sizes of these fried resistors but I guarantee you these are the correct wattages. I have replaced both of mine in this fashion. NO MORE POPPING!!! Functioning properly now with no issues for nearly 3 weeks. Cost me a total of $5.35 since I already had a soldering iron, solder, and flux. The cost was solely for the replacement resistors and majorly shipping of these tiny parts! All in all way less than paying $140 for a new amp or entirely new sub. If you have the need I will post pics of the old board resistors and the replaced resistors. However, if you do not need these I'd prefer not to pull the amp back out of the unit.

Hope this helps y'all save some bucks$$$!!!

Your home economically-conscious friend,

Hlmartin22
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post #10 of 16 Old 02-06-2015, 10:02 AM
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To try and clarify my previous posts:

Hi Adam and thanks for your inquiry about my work on my JBL Venue Sub12. Sucks to hear you're having problems as well.
First off I will say that my original problem was the same as yours by your description (after a certain period of time my sub would start popping).
Therefore I pulled the amp, saw obvious problems of overheating around the R6 and R9 resistors. So, initially, I replaced ONLY these resistors with the aforementioned resistance ratings. Only replacing these resistors solved the problem. My sub functioned flawlessly again for several months.
Later, I began having additional problems which I described in another post. So I pulled the amp again and spotted a leaky non-polar capacitor (C72) so I replaced that as well.

So I did replace the one cap; however, I didn't have to replace any caps to solve the popping problem. I am interested to know which capacitors the guy on Ebay said he has to replace to fix the issue. I wonder if it's the primary 3300 microfarad caps? Mine appear to be intact (no leaking) so I have not fooled with them. Perhaps he'd be willing to share? Or maybe he wants to keep that private if he has secured business through his knowledge. Don't be greedy Ebay guy!!! Hope this helps you and let me know if you get anymore info out of Mr. Ebay.
hlmartin22

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Originally Posted by velponator View Post
To hlnmartin!!! I tried msg'ing you but I don't have those privileges.

Hey man! I saw your post about fixing your JBL VENUE SUB12. Mine has worked great for years and then awhile back, if it's on for more than 2 hours, just starts popping and I have to turn it off. I see that you replaced 2 resistors and it's fixed? I contacted a guy on EBAY who said he has to replace capacitors to fix the problem. Did you JUST do the resistors and it worked? Or did you have to do capacitors too? Also, did you have the same problem as me? Sorry for the jumbled message, I'm running to work!

Thanks in advance,
Adam
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post #11 of 16 Old 02-06-2015, 10:16 AM
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Popping noises in a class D plate amp could come from multiple sources, but most likely due to failed capacitors inducing instability somewhere and causing intermittent oscillations. Capacitors tend to fail as they get old especially with counterfeit electrolytic capacitors coming from Taiwanese manufacturers with the 'capacitor plague' stolen, incorrect electrolyte formula (see Wikipedia).

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

These counterfeit capacitors are in just about every sort of consumer equipment sold over the past decade and IMO responsible for most of the premature failures in consumer audio manufactured with them.

I had a GeForce graphics card where every single electrolytic capacitor swelled up on top and split apart at the 'no explode' safety score marks before I noticed and stopped using it, fearing a fire. Quality brands are not guaranteed free of these capacitors since the purchasing agents were (probably) not aware the capacitors were counterfeit when purchasing from Taiwanese manufacturers and the prevalence of such capacitors makes widespread recalls financially devastating to manufacturers. Sweeping the problem under the rug is standard modus operandi, with maybe one or two manufacturers offering free out-of-warranty repairs (to prevent class action lawsuits IMO) to anyone who complains loudly enough.

Just because Wikipedia has declared the problem over does not mean that unscrupulous or sloppy manufacturers did not continue using up bad inventory in later years, maybe even continuing to this day.

Unlikely that changing resistors will fix the problem. Physically large resistors are chosen for their power dissipation capacity and normally get hot during operation. The (all too common) discoloration around the pads of those resistors is probably due to normal operating temperature in the resistors and is likely normal for that amp especially when it starts going unstable. It is unlikely the resistors are bad (overheated resistors discolor, swell up, bubble or crack, and eventually burn through like a fuse, causing permanent interruption of operation) and even if they are degraded in component value tolerance from long term normal heat, or failed completely, it is even less likely that the resistors are the root cause of the problem too. Resistors are unlikely to just burn out for no reason. Changing resistors may affect the oscillation by tweaking the tuning of the circuit somewhat with the variation in resistance, but excluding freshman design/manufacturing error in specifying the resistors' power dissipation capacity, there is nearly zero chance the root cause will actually be fixed and nearly 100% chance the problem will recur shortly IMO.

The best way to identify failed components is to diagnose them in-circuit then remove and test them with instrumentation. Such repairs should only be done by someone with adequate troubleshooting skills, proper facilities, and with a schematic or better yet service manual, something difficult to find for plate amplifiers outside of an authorized repair service.

This is not the infamous and IMO widespread (due to improper design) Onkyo HDMI local power supply capacitor failure that is trivial to diagnose and repair. Plate amplifiers use Class D analog circuitry that the average DIYer may have great difficulty comprehending. Without a large body of experience successfully repairing them in the DIY marketplace on your specific brand or model exhibiting these exact symptoms, it may be impossibly challenging. The most likely route to successful, ignorant DIY repair is to remove and measure each electrolytic capacitor to determine which capacitors are failing, if any.

I suggest checking ebay for a budget plate amp repair service that will fix yours for you if you do not want to replace it. Sometimes you can find a good deal but whether any such 'unauthorized' repair service will help you depends primarily on whether they can get the service manual and replacement ICs. Even then repair may still be less affordable than the replacement.

I can troubleshoot fine but decided to replace my out-of-production BASH model with a similar model from Parts Express because cutting and drilling adapter shims to mount the thing was far easier than troubleshooting the failed amp without proper facilities and $120 was a comparative bargain over finding a replacement subwoofer with similar sound.
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post #12 of 16 Old 02-06-2015, 10:34 AM
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Great Info!

This is great information! Thanks for adding it to the thread. I have continued to troubleshoot this issue despite my ignorance out of sheer fascination with attempting to repair my own components. Luckily for this amp... the service manual is readily available at an address I will have to re-post due to link restrictions. But you're right it can still be challenging to understand. When I'm dealing with "either I fix it or it goes in the trash" I like to try and fix it. Reluctant to pull each cap to test it with my capacitance multimeter but I guess it's time I should. It makes sense that replacing the resistors could simply be a bandaid on a bullet hole. Thanks again for the additional info!
hlmartin22

Quote:
Originally Posted by CherylJosie View Post
Popping noises in a class D plate amp could come from multiple sources, but most likely due to failed capacitors inducing instability somewhere and causing intermittent oscillations. Capacitors tend to fail as they get old especially with counterfeit electrolytic capacitors coming from Taiwanese manufacturers with the 'capacitor plague' stolen, incorrect electrolyte formula (see Wikipedia).

These counterfeit capacitors are in just about every sort of consumer equipment sold over the past decade and IMO responsible for most of the premature failures in consumer audio manufactured with them.

I had a GeForce graphics card where every single electrolytic capacitor swelled up on top and split apart at the 'no explode' safety score marks before I noticed and stopped using it, fearing a fire. Quality brands are not guaranteed free of these capacitors since the purchasing agents were (probably) not aware the capacitors were counterfeit when purchasing from Taiwanese manufacturers and the prevalence of such capacitors makes widespread recalls financially devastating to manufacturers. Sweeping the problem under the rug is standard modus operandi, with maybe one or two manufacturers offering free out-of-warranty repairs (to prevent class action lawsuits IMO) to anyone who complains loudly enough.

Just because Wikipedia has declared the problem over does not mean that unscrupulous or sloppy manufacturers did not continue using up bad inventory in later years, maybe even continuing to this day.

Unlikely that changing resistors will fix the problem. Physically large resistors are chosen for their power dissipation capacity and normally get hot during operation. The (all too common) discoloration around the pads of those resistors is probably due to normal operating temperature in the resistors and is likely normal for that amp especially when it starts going unstable. It is unlikely the resistors are bad (overheated resistors discolor, swell up, bubble or crack, and eventually burn through like a fuse, causing permanent interruption of operation) and even if they are degraded in component value tolerance from long term normal heat, or failed completely, it is even less likely that the resistors are the root cause of the problem too. Resistors are unlikely to just burn out for no reason. Changing resistors may affect the oscillation by tweaking the tuning of the circuit somewhat with the variation in resistance, but excluding freshman design/manufacturing error in specifying the resistors' power dissipation capacity, there is nearly zero chance the root cause will actually be fixed and nearly 100% chance the problem will recur shortly IMO.

The best way to identify failed components is to diagnose them in-circuit then remove and test them with instrumentation. Such repairs should only be done by someone with adequate troubleshooting skills, proper facilities, and with a schematic or better yet service manual, something difficult to find for plate amplifiers outside of an authorized repair service.

This is not the infamous and IMO widespread (due to improper design) Onkyo HDMI local power supply capacitor failure that is trivial to diagnose and repair. Plate amplifiers use Class D analog circuitry that the average DIYer may have great difficulty comprehending. Without a large body of experience successfully repairing them in the DIY marketplace on your specific brand or model exhibiting these exact symptoms, it may be impossibly challenging. The most likely route to successful, ignorant DIY repair is to remove and measure each electrolytic capacitor to determine which capacitors are failing, if any.

I suggest checking ebay for a budget plate amp repair service that will fix yours for you if you do not want to replace it. Sometimes you can find a good deal but whether any such 'unauthorized' repair service will help you depends primarily on whether they can get the service manual and replacement ICs. Even then repair may still be less affordable than the replacement.

I can troubleshoot fine but decided to replace my out-of-production BASH model with a similar model from Parts Express because cutting and drilling adapter shims to mount the thing was far easier than troubleshooting the failed amp without proper facilities and $120 was a comparative bargain over finding a replacement subwoofer with similar sound.
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post #13 of 16 Old 02-06-2015, 10:35 AM
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Here's the link to the service manual.

http://www.manualslib.com/manual/793...12.html#manual

Quote:
Originally Posted by hlmartin22 View Post
This is great information! Thanks for adding it to the thread. I have continued to troubleshoot this issue despite my ignorance out of sheer fascination with attempting to repair my own components. Luckily for this amp... the service manual is readily available at an address I will have to re-post due to link restrictions. But you're right it can still be challenging to understand. When I'm dealing with "either I fix it or it goes in the trash" I like to try and fix it. Reluctant to pull each cap to test it with my capacitance multimeter but I guess it's time I should. It makes sense that replacing the resistors could simply be a bandaid on a bullet hole. Thanks again for the additional info!
hlmartin22
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post #14 of 16 Old 02-08-2015, 10:06 AM
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Results of checking all component side caps.

I have pulled every capacitor on the component mounted side of the PCB for the Venue Sub12. To my surprise there are 6 capacitors reading below 80% of their rated capacitance. As a hobbyist I have always relied on noting a visible problem (esp. a leak/bulge with capacitors) to diagnose a potential issue. I'm assuming these electrolytic caps have "dried up". What's that they say about assumptions? Well anyways here's the summary of the bad caps on my board:

C4 - 22uF /25V @ 5%
C9 - 22uF /25V @ 25%
C12- 330uF/16V @ <1%
C35- 10uF /25V @ 30%
C64- 100uF/25V @ 70%
C65- 47uF /16V @ 10%

I am ordering replacements immediately and will be putting the amp back together when they arrive. With any luck my next post will be a positive one.
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post #15 of 16 Old 03-15-2015, 01:16 PM
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To follow up

I replaced all the caps that read below 80% of functionality and put the amp back in the sub. This did seem to stop all popping or any other abnormal sound coming from the driver while in use. However, there still must be something wrong with the amp. My standby relay switches on and off frequently when watching movies or TV. I've messed with the crossover and LPE settings to no avail... so unless it's an issue with my cable or the signal coming from my receiver then it must still be an issue with the amp (which I'm assuming it is). Not a big deal but it can be a little annoying. When I'm listening to music the relay stays on and the sub sounds clean; this only occurs when watching something that goes long periods without low frequencies. Maybe the relay just needs to be replaced but I get the feeling it is functioning normally and the signal in the traces prior to the relay is fluctuating in a way it shouldn't.
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post #16 of 16 Old 03-15-2015, 02:27 PM
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CherylJosie,

I agree trouble shooting class d amps is a challenge. I been doing component level repair around 40 years and they give me headaches. I lucked out a few times by replacing puffed up power supply caps. I recently sent out my Paradigm sub amp because I couldn't handle it. They fixed it in no time.

When I do replace those caps., I always try to buy ones of the same value, but with a higher voltage rating. Gotta pay attention to physical size though. I usually buy from Newark Electronics. And yes, dis coloration around resistors can just be from normal use.

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