Oops. Popped LM3886?

[tbj]

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.

 

[sofaspud]

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]

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]

. . . 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]

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.

The bulb tester would have helped save the speaker though.

 

[tbj]

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.