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Old 4th August 2016, 12:41 PM   #1
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Default Need help repairing JBL amp

I have a JBL amp which is working BUT there's something wrong with 2 of the outputs.
Front left output just buzzes and front right produces no sound at all.
I opened it yesterday and just from looking at the board I see nothing wrong with it so I'm not sure where to go from there.
I'm also the noob in electronics but willing to learn a lot!
I attached pics of both sides of the board (these are only until I charge my camera and learn how to take better pictures). Marked with red are those outputs.

http://i.imgur.com/MZkiRnq.jpg
http://i.imgur.com/njnDWp6.jpg

Last edited by jimmies; 10th August 2016 at 02:09 PM. Reason: Better pics (only links).
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Old 4th August 2016, 05:02 PM   #2
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I can't really offer any suggestions on this since I have no experience with them but I will tell you not to apply power without having the amplifier ICs tightly clamped to the heatsink.
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Old 5th August 2016, 02:27 AM   #3
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A common problem in amps like this is bad small electrolytic capacitors. It looks like there may be 2 on each chip, plus a few among the equalizer ICs. You could just replace all of them except for the 4 large cans (probably 2200uF @ 16V). If the small ones are wet underneath, than they are definately bad. Clean the electrolyte off the board and check for corroded traces under the caps.
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Old 6th August 2016, 02:49 PM   #4
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Send to United Radio Service - they are the only JBL repair center. Automotive Electronics | United Radio
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Old 6th August 2016, 06:13 PM   #5
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United Radio does good work but unless you have very deep pockets, you should get a price on the repair charge, including shipping before sending it to them.
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Old 10th August 2016, 11:07 AM   #6
Greg32 is offline Greg32  Australia
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do you have the ability to test the amplifier out of the vehicle? i had a problem like you described in a jeep and it turned out to be an intermittent fault/earth in the factory speaker wiring. Greg
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Old 10th August 2016, 06:45 PM   #7
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Board looks pretty clean, I don't think there are any leaked capacitors. Though not sure about some of them, because they are covered with silicone. I'm a bit reluctant about changing parts without checking them first.

Quote:
Originally Posted by Snydersound View Post
A common problem in amps like this is bad small electrolytic capacitors. It looks like there may be 2 on each chip, plus a few among the equalizer ICs. You could just replace all of them except for the 4 large cans (probably 2200uF @ 16V). If the small ones are wet underneath, than they are definately bad. Clean the electrolyte off the board and check for corroded traces under the caps.
Now I have it at home, but haven't tested yet. I'm not sure I would know how to.
Do you mean you found there was no problem with the amp, but with speaker wiring?

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Originally Posted by Greg32 View Post
do you have the ability to test the amplifier out of the vehicle? i had a problem like you described in a jeep and it turned out to be an intermittent fault/earth in the factory speaker wiring. Greg
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Old 11th August 2016, 01:47 AM   #8
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It's gonna be really hard to test this amp unless you're confident you know the pin assignment on the plugs. If you google the chip name, you should find the chip pinout, so you can test voltages on the pins when powered up (with heatsink installed!). Should be about 1/2 supply voltage on output pins ( a few chips have about 2.5 v, but outputs should be the same). both inv and non-inv inputs should have almost exactly the same voltage. If input voltages are different, there may be voltage leakage. Also, bias bypass capacitor may be shorted ( low voltage on IC bias cap).
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Old 12th August 2016, 12:57 AM   #9
Greg32 is offline Greg32  Australia
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Now I have it at home, but haven't tested yet. I'm not sure I would know how to.
Do you mean you found there was no problem with the amp, but with speaker wiring?[/QUOTE]

Yes there was no problem with the amplifier, the issue was in the vehicle wiring.
it was confusing at first as it was intermittent. you really need to be able to test all aspects of the installation to rule out other possible causes. Greg
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