I'm guessing you haven't a scope as that would show where the problem is in seconds.
I still think the LM3886 is the main suspect but a way to check on the signals is to carefully use either headphones or a small speaker and probe the opamp outputs and see if you can hear good audio.
You must be careful doing this and be careful of your ears if using headphones. A speaker is best.
The testing involves connecting one lead of the speaker or phones to ground and placing a resistor of around 470 ohms (it's not critical) in series with the other lead. Then probe the opamp outputs with that lead and see if you can hear faint but good audio.
Look at the circuit. Pin 7 of IC202 is the obvious point to test first as that is the output of all the preamp stages that feed the LM3886.
I still think the LM3886 is the main suspect but a way to check on the signals is to carefully use either headphones or a small speaker and probe the opamp outputs and see if you can hear good audio.
You must be careful doing this and be careful of your ears if using headphones. A speaker is best.
The testing involves connecting one lead of the speaker or phones to ground and placing a resistor of around 470 ohms (it's not critical) in series with the other lead. Then probe the opamp outputs with that lead and see if you can hear faint but good audio.
Look at the circuit. Pin 7 of IC202 is the obvious point to test first as that is the output of all the preamp stages that feed the LM3886.
A scope... wonderfull 
Connect the scope ground lead to the main ground in the amp. Set the scope to around 0.1 or 1 volt/div and the timebase to around 5ms/div.
Connect the amp up and switch on and with a suitable input (CD playing etc into the line input) see if you can see clean audio on the "final" opamp output (Pin 7 of IC202).
If so then it's pretty certain the LM3886 is faulty.
If not then work back toward the input checking the audio on each opamp output.
If you look at the circuit the signal path is arrowed.
Connect the scope ground lead to the main ground in the amp. Set the scope to around 0.1 or 1 volt/div and the timebase to around 5ms/div.
Connect the amp up and switch on and with a suitable input (CD playing etc into the line input) see if you can see clean audio on the "final" opamp output (Pin 7 of IC202).
If so then it's pretty certain the LM3886 is faulty.
If not then work back toward the input checking the audio on each opamp output.
If you look at the circuit the signal path is arrowed.
What I've found right off the bat, comparing the 100hz test signal at its source to the output on pin 7 of IC202, the input signal shows up clean at the source and wide and fuzzy at the output. Should I be adjusting the level on the sub at all to see if it makes a difference? Running the audio from my MacBook to the sub, as I raise the volume from my MacBook, the audio increases slightly, then drops off quickly. Still faint and fuzzy overall. Do I keep tracking the signal or is IC202 my problem? Thanks!
The level at IC202 is dependant on the level setting control so now go to pin 1 of IC202 and see if the signal is there. It should be. If you turn the level control up then that signal should appear at pin 7. Try and understand the circuit
how the signal progresses from each stage.If that doesn't reveal anything then start from the input and check the signal on pins 1 and 7 of each opamp apart from pin 1 of IC102.
Op amps are usually extremely reliable.
Same issue
Hello all, I have the exactly same issue. I checked the op amp pins 4 and 8, reads -38 vdc. I checked pins 1 and 7, reads -39vdc. This means i have to replace the op amp, correct. Would there be anything else I should replace just a as a precaution. Zener diodes have already been replaced.
Hello all, I have the exactly same issue. I checked the op amp pins 4 and 8, reads -38 vdc. I checked pins 1 and 7, reads -39vdc. This means i have to replace the op amp, correct. Would there be anything else I should replace just a as a precaution. Zener diodes have already been replaced.
Cool thread.
Here is the same model amp I just picked up.
Looked like somebody thought these diodes were optional and put in jumpers. Obviously it doesn't work.
I am about to swap the jumpers out for the diodes, what's the chance that the whole thing is fried because it was turned on with jumpers?
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