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Old 2nd February 2010, 10:28 AM   #1
Ted205 is offline Ted205  United Kingdom
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Default signs of a dead lm3886

Just wondering what peoples experiences are with dead LM3886s'.

In general terms do they output DC?
Draw to much current from the powersupply?
Are they susceptible to static damage?
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Old 2nd February 2010, 10:44 AM   #2
Mooly is offline Mooly  United Kingdom
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Could be anything symptom wise... usually a hole blown in the side
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Old 4th February 2010, 12:30 PM   #3
Ted205 is offline Ted205  United Kingdom
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so there is no way you can check to see if the chip is ok? I dont have a new lm3886 to check against.
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Old 4th February 2010, 12:34 PM   #4
AndrewT is online now AndrewT  Scotland
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I accidentally swapped one of the AC leads for the centre tap lead feeding the rectifier. i.e. ac-ac-ct instead of ac-ct-ac.
Killed the 3886, but did not leave any evidence of overheating and certainly not any physical damage.
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Old 4th February 2010, 01:03 PM   #5
Mooly is offline Mooly  United Kingdom
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Quote:
Originally Posted by Ted205 View Post
so there is no way you can check to see if the chip is ok? I dont have a new lm3886 to check against.
Of course... you fault find... it is just an opamp of sorts after all.

With no load connected,
Measure all supplies at the IC.
Confirm all grounds OK
Confirm the inputs are at zero volts DC (assuming it's configured in a "normal" application such as in the data sheet.
Confirm the output is at zero volt DC.
Confirm the mute pin is doing what you expect voltage wise.

If it passes all those tests measure the current draw and check against the data sheet.

Make sure the feedback network is correct.

If you do all that you will most likely find something amiss that either points to a construction error, or else a destruction error that occured and that has zapped the IC.
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Old 4th February 2010, 01:56 PM   #6
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Quote:
Originally Posted by Ted205 View Post
In general terms do they output DC?
The other way round. If you get DC at rail level on the output, when the input is 0 V, the IC is fried.

Quote:
Originally Posted by Ted205 View Post
Draw to much current from the powersupply?
If a load is connected, yes. If no load is connected, maybe.

Quote:
Originally Posted by Ted205 View Post
Are they susceptible to static damage?
If the voltage level is high enough, yes.
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Old 4th February 2010, 03:59 PM   #7
Ted205 is offline Ted205  United Kingdom
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thanks for the useful input guys.
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Old 23rd August 2014, 03:57 PM   #8
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Quote:
Originally Posted by Mooly View Post
Of course... you fault find... it is just an opamp of sorts after all.

With no load connected,
Measure all supplies at the IC.
Confirm all grounds OK
Confirm the inputs are at zero volts DC (assuming it's configured in a "normal" application such as in the data sheet.
Confirm the output is at zero volt DC.
Confirm the mute pin is doing what you expect voltage wise.
Mooly- My LM3886 is not working...could you pls elaborate on what you mean by confirm the mute pin is doing what you expect voltage wise?

Thanks,
Mohit
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Old 23rd August 2014, 04:04 PM   #9
AndrewT is online now AndrewT  Scotland
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The mute pin operation is described in the datasheet.

With no connection to mute pin the amplifier is OFF.

The graph shows the CURRENT (typically 0.2mAdc) that needs to flow into the mute pin to turn the amplifier fully ON. Less current only turns on the amplifier a little bit. More current ensures that the amp does not start to turn off if voltages drop. But don't go off the graph, or you could damage the mute function when voltages are very high. Aim for ~0.5mAdc when supply voltage is normal.

You do this by connecting a resistor from -ve supply to mute pin.
That resistor supplies the mute pin current.
Read the instructions in the datasheet. All the voltages and currents are in there.
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Old 23rd August 2014, 05:15 PM   #10
Mooly is offline Mooly  United Kingdom
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Quote:
Originally Posted by Mohitkmittal View Post
Mooly- My LM3886 is not working...could you pls elaborate on what you mean by confirm the mute pin is doing what you expect voltage wise?

Thanks,
Mohit
As Andrew has posted above ^

(you might be better starting a new thread for your specific issue if you can't sort it easily, this one is over 4 years old)
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