Electronics > Projects, Designs, and Technical Stuff
I would like help in determining why this amp doesnt work
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Hextejas:
It was working and apparently something came loose when I moved it from the bench to the audio room.
This is the right channel and the left channel works.
I dont know where to take voltage readings or to see what the signal looks like with a scope.

I put a 1khz signal in and tried to trace it through to the output and I got lost. Ditto reading voltages.
I tried comparing the voltages and waveform to the left channel but I dont know what to look for. For example, what the waveform should look like and where to look for it,
Richard Crowley:
You could start by connecting the black lead of your meter to ground.
With the load (speaker) connected but no audio connected to the output.
And the power turned on.  COnfirm that the + power and - power are going into each channel properly.
Then go to each pin of the integrated circuits and record the voltage on each pin.  On BOTH channels.
Are the voltages the same on the functioning channel as on the failed channel?

Be careful to not short anything when you are probing around with the circuit powered up.
A tiny slip of the probe could short out adjacent pins/pads which could destroy the IC.

Since there is only one active component (the integrated circuit), there isn't much "signal tracing" opportunity here.

Since you have a functioning channel, you could establish exactly what the scope sees when the circuit is working properly.
Audioguru:
Maybe the output voltage of the non-working channel suddenly went to a high voltage positive or negative and blew out the speaker because the other supply voltage came loose.
Without a speaker connected and with no input signal, measure the DC voltage at the output. It should be very close to 0VDC. Also try its speaker on the channel that works.
Hextejas:
I took a bunch of readings at the pins of the LM3886 and some are different. I tried interpreting them vs the datasheet, but that is beyond me.
Here are the readings.
Audioguru:
Inputs pin 9 and pin 10 and output pin 3 should always be about 0VDC but yours go to a high positive voltage when the GOOD channel has no signal. That will destroy the GOOD speaker.
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