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How to check a LM3886 to see if it is bad.

Ralph Mcintire
Prodigy 10 points
Other Parts Discussed in Thread: LM3886

I have an audio amplifier that has a left and right channel output board. Each of these boards have 3 LL3886 parts on them. One is used for internal output and the other 2 are used for external output ,tied together.

What happenned is the external output for both left and right channels were tied together, (+left, +right ) were tied together ' and both( -left and - right )were tied together. The amp worked like this for 20-40 hrs. producing output and I was told the sound was good. But now nothing. I know this is very bad to tie outputs together and now there is no output at all on the external ouput, but the internal speakers work fine.

I have the unit apart and would like to know if I can test the LM3886 to see if it is bad , remember there are 2 of these being used in the external output for each channel. I see now signs of damage to the chips . The data sheet says these have alot of protection built into them but this tie together of the outputs was bad.

I am a EET and was hoping you could offer a way to check them , or you are going to tell me that they have to be bad . It surprises me that they would of functioned for 40 hrs. hooked up this way.

Thanks Ralph

  • 0
    TI__Guru**** 189401 points

    Hi, Ralph,

    I would separate the outputs, and feed an input signal. Look at the inputs and outputs and see what you get.

    If the input signal looks good, and there is no output, then the IC is bad. If the input signal is bad, then the problem is somewhere else in your system.

    Good luck!

    -d2

  • 0
    TI__Intellectual 1240 points

    Hello Ralph-san,

    I'll make some comment on your connection.

    If you want to drive like pararell for left and right channel, you need to put ballast resistor on each amplifier outputs such as 0.1 to 0.2 ohms because if you connected both outputs together, amplifier DC offset cuases big current flow between both output. The ballast resistor supress this current. And also you need to take summention for left and right signal on the input side as well. Then Then the both output have same phase (left+right) . The it will work fine the pararell drive approach. Please try this way.

    Best regards

    T NAOKAWA