Logic 7 amp not working. Please help. - diyAudio
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Old 28th June 2015, 05:14 AM   #1
jin108 is offline jin108  New Zealand
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Default Logic 7 amp not working. Please help.

Here are a few pics of my Logic7 amp circuit board. Its from a BMW 2007 E90.
I pulled it apart because the underseat woofers were barely audible.

Is there anything obviously wrong with it? Is the green goo supposed to be there?

I am a complete noob at this. If its possible for me to fix it id like to rather than taking to a repair shop.
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File Type: jpg C360_2015-06-28-15-48-36-550.jpg (357.9 KB, 74 views)
File Type: jpg C360_2015-06-28-15-48-48-535.jpg (434.7 KB, 69 views)
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Old 28th June 2015, 03:04 PM   #2
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I have no information on this amp but the green fixative is likely silicone and is used to prevent the legs on the capacitors from breaking.
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Old 28th June 2015, 11:00 PM   #3
jin108 is offline jin108  New Zealand
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Quote:
Originally Posted by Perry Babin View Post
I have no information on this amp but the green fixative is likely silicone and is used to prevent the legs on the capacitors from breaking.
Thanks good to know.

A local repair shop told me it cant be fixed because its digital and must be replaced. Problem is these amps are US 800 thereabouts new. So thats out of the question.

What is the correct way to test the ICs with a multimeter? Can you link me a guide or something to follow? I have read the ICs can be replaced which should hopefully fix it.

Thanks!
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Old 28th June 2015, 11:02 PM   #4
jin108 is offline jin108  New Zealand
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These are the specs i was able to find on the amp:

9 channels, 13 loudspeakers
• 1 mid-range loudspeaker, middle, 100 mm
• 2 treble loudspeakers, front 26 mm
• 2 mid-range loudspeakers, front 100 mm
• 2 bass loudspeakers, 217 mm
• 2 mid-range loudspeakers, rear door, 100 mm
• 2 mid-range loudspeakers, rear shelf, 100 mm
• 2 treble loudspeakers, rear shelf, 26 mm
Bandwidth: 30 Hz to 20.000 Hz
Max. acoustic pressure: 110 dB
Amplifier power:
2 x 70 W (4 Ω) Bass
7 x 40 W (2 Ω)
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Old 29th June 2015, 12:07 AM   #5
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If the audio from the woofers was clean but low, I would expect the problem to be elsewhere. Generally when an amp fails, audio is absent or distorted.

It's difficult to test ICs like these with a multimeter except to compare the readings from one to another.

If they have the original part number on the ICs, you may be able to get replacements but many times, OEM amps like these have markings that are specific to the vehicle or amp manufacturer.
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Old 29th June 2015, 12:33 AM   #6
jin108 is offline jin108  New Zealand
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On the BMW forums its a well reported problem of the amps failing to power the woofers. I have also removed the woofers and they are working perfectly when i hooked them up to my home stereo.

So I have cleaned up all the thermal paste off the ICs and the 6 large ones have no markings but the three small ones do. Two of the small ICs have the same number so im guessing they are the bass ICs - as the amp spec has two channels for bass.

I found a datasheet for the IC too. Does that help in order to test the ICs?

Or can I just buy two of them and replace?
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Old 29th June 2015, 02:23 AM   #7
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Those are FETs and likely drive a power transformer.

The numbers would be on the black side of the larger ICs. Be aware that forcing the IC up off of the board may damage the IC and/or the board.

Has anyone on the BMW board replaced the amp and that resolved the problem?
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Old 29th June 2015, 02:36 AM   #8
jin108 is offline jin108  New Zealand
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From what I have read on the forums its either replace or send to someone to repair. There is no useful DIYs unfortunately.

Here is a link to the datasheet I found - http://www.mouser.com/ds/2/389/CD00001329-250093.pdf

Is this a FET? Does that mean it is not a IC and nothing to do with the bass?
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Old 29th June 2015, 04:37 AM   #9
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My mistake. The rectifiers convert the AC out of a transformer to DC.

Just a guess but I'd say that the sub amp has a switching power supply. The FET and rectifiers could be for that supply. The rest of the ICs likely operate from 12v.

If the audio is clean but low, that's rarely a power supply problem. When the supply fails, the audio is generally lost or very distorted.
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Old 29th June 2015, 06:03 AM   #10
jin108 is offline jin108  New Zealand
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Should I change the caps then?
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