Any help on repairing a bad sub amp? - AVS Forum
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post #1 of 8 Old 08-16-2012, 08:32 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 8 Old 08-16-2012, 04:25 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 8 Old 08-16-2012, 07:25 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 8 Old 08-16-2012, 07:42 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 8 Old 12-28-2013, 12:34 PM
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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,

 

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post #6 of 8 Old 10-11-2014, 09:07 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 8 Old 10-12-2014, 11:23 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 8 Old 11-03-2014, 12:04 PM
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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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