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-   -   Oops. Popped LM3886? (http://www.diyaudio.com/forums/chip-amps/223231-oops-popped-lm3886.html)

tbj 9th November 2012 08:25 PM

Oops. Popped LM3886?
 
I am building an LM3886-based chip amp. One channel is working, decided to throw the other one together tonight and stupidly managed to connect the V- rail directly to pin 8 (the mute pin) rather than pin 4. I heard a funny noise and the negative rail went to full -ve.

Turned it off straight away and corrected the wiring, but now the chip does nothing but show full negative voltage on the speaker output. Have I popped it? Is it a usual failure mode for these things?

Rather peed off at myself, given that these things cost over a fiver each. :mad:

sofaspud 9th November 2012 08:59 PM

Quote:

Have I popped it?
I'm afraid so. The mute pin is designed for 0.5mA current and it's likely you greatly exceeded that.

AndrewT 10th November 2012 02:46 PM

The mute pin is connected to the input stage.
It's likely you flashed Vcc right through all the components in that input stage.

This may well be the first mis-wiring that a bulb tester cannot protect against !

danielwritesbac 12th November 2012 06:51 AM

Quote:

Originally Posted by tbj (http://www.diyaudio.com/forums/chip-amps/223231-oops-popped-lm3886.html#post3235192)
. . . now the chip does nothing but show full negative voltage on the speaker output. Is it a usual failure mode for these things?

Yes, that is the typical failure mode for chip amplifiers.
I like both chip amplifiers and speakers, so I like output caps too.
It is good to include speaker protection in chip amplifier builds.

johnr66 12th November 2012 04:10 PM

Quote:

Originally Posted by AndrewT (http://www.diyaudio.com/forums/showthread.php?p=3236070#post3236070)
The mute pin is connected to the input stage.
It's likely you flashed Vcc right through all the components in that input stage.

This may well be the first mis-wiring that a bulb tester cannot protect against !

I bought some amp ICs from ebay. One came with a supply rail on the output pin right from the seller. The bulb tester wouldn't have helped there either. :D

The bulb tester would have helped save the speaker though.:(

tbj 12th November 2012 04:19 PM

Quote:

Originally Posted by johnr66 (http://www.diyaudio.com/forums/showthread.php?p=3238730#post3238730)
The bulb tester would have helped save the speaker though.:(

Ouch!

That is why one should test into a dummy load, monitoring the output using an oscilliscope. Resistors are cheap, speakers are not. :p


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