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Old 28th January 2006, 12:26 PM   #1
waltson is offline waltson  Finland
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Default LM3875 BrianGT kit not working

Hi all.

Suddenly the other channel of my gainclone stopped working.
When I opened the case, I noticed that the V- wire from the power supply was loose. I reattached it and it still doesn't work. Is it possible, that the loose wire caused the chip to fry? What could I do to find out the reason for the malfunctioning?

Thanks.
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Old 28th January 2006, 12:32 PM   #2
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Your lucky that the ic dident fry your speaker when the -Ve wire loosened.
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Old 28th January 2006, 04:58 PM   #3
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I have never destroyed a LM3875 or 3886 so I don't know possible ways of destroying. You can try at least to check input bias currents, voltages at the inputs and the output. Maybe also the current consumption in both supply voltages.

Be prepared for a fried chip.
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Old 28th January 2006, 05:03 PM   #4
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The chip won't break, or damage the speakers, when one of the supply rails is missing.

Check the PS first, if it's producing proper voltages.
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Old 28th January 2006, 05:05 PM   #5
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I tried to destroy two parallel lm3875 on purpose once, when nothing worked after hours of trying, i had only one thing left to try, shorting the outputs and max the volume. That finally did it.
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Old 28th January 2006, 05:07 PM   #6
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Without signal maxed, shorting the outputs won't break the chip either (at least in half an hour or so).
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Old 28th January 2006, 05:27 PM   #7
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If these ics breaks just like that its factory error. Tsese ICs wont break unless u really try to break them like overvolt them or shorting the outputs with volyme at max.
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Old 28th January 2006, 05:39 PM   #8
john65b is offline john65b  United States
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Default My Bad Experience...

I broke the Number One Rule of soldering the other night, I was rushing to finish soldering up the last of my LM3886 amp while EXTREMELY TIRED.

The amp is configured as a single Toroidal Tranny/rectifier/cap bank. I finished and powered her up and saw a little puff of smoke out of my Left Channel LM3886 (yes, they are heat sinked). I then put her away for the night and went to sleep. After work the next day I looked her over and I completely forgot to attach both amps to power GROUND.

I replaced the smoked amp board with a new one (the other channel seemed fine), connected the Power GROUNDS to both amp boards and all was good with the amp.

Now the smoked chip. I looked at under a loupe and the #6 pin is charred - and #6 pin is No Connection. I am perplexed at what I could have done. It is next to the #7 pin which is GROUND. Looked over the PCB and nothing else seems amiss.

Any thoughts? And beside reconnecting the board, is there any way I can check to see if the LM3886 chip is really fried with a MM to the chip pinouts?)

I can get a new chip for $3.50 and replace it, but these chips are pretty indestructable, aren't they? And I hate DESOLDERING !
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Old 28th January 2006, 06:31 PM   #9
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If a ic fries, cut the legs off close to the ic and then just desolder them one as a time.
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Old 28th January 2006, 08:00 PM   #10
Nordic is offline Nordic  South Africa
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You wanna fry one quick? leave a solder trace from one of the voltage rails to the output, bang!!!!!!!!!!!!
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