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Old 5th February 2013, 08:08 AM   #51
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It's not straight DC. The channel is oscillating. It appears as DC because the oscillation waveform isn't symmetrical (well, that's a guess).

Clamp the outputs and set the bias so that it goes back to a straight line (minimum bias that achieves that). What is the DC voltage across each of the 0.1 ohm source resistors?
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Old 5th February 2013, 08:23 AM   #52
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I think you are correct, I will do that now. I replaced all the outputs and drivers on that side of the amp.

Its acting like an un biased Power 650. If you view the output throught the scope at an idle, you have to increase the bias to get a straight line and get rid of the noise.

The lower the bias the bigger the haze or noise.

I will check what you asked right now.
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Old 5th February 2013, 08:36 AM   #53
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Please read post #52 first.

I set the bias on the 2 channels just until the line went straight. Its drawing about 2 amps current.

R449 0.007 vdc
R436 0.007 vdc
R349 0.033 vdc
R336 0.033 vdc

These voltages were measured across the source resistors.

All channels produce clean audio, but 2 only do as long as the bias is set. I have not tested on speakers yet, but as far as a waveform on the scope 2 have bad ascillation if the bias is not set.
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Old 5th February 2013, 01:44 PM   #54
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I don't know which channel you set the bias on first so try this. Set the bias fully CCW on those channels and bias the 300 series channel first, then the 400 series channel.

Note the voltage across the 0.1 ohm resistors.

Now go back to fully CCW and bias the 400 then the 300 series channel and note the resistor voltage.

I'm trying to determine if one channel is causing the other channel to oscillate. If only one channel is actually defective, maybe stopping it from oscillating will allow the other channel to be set at a normal bias.
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