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Old 13th July 2010, 03:25 PM   #11
shawnk is offline shawnk  United States
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When I said the "bias pot has no effect" I meant that current flow will not increase or decrease at all by adjusting the pot.

Thanks!
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Old 13th July 2010, 03:57 PM   #12
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Which channel is distorted (color of speaker wire for distorted channel)?
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Old 13th July 2010, 04:05 PM   #13
shawnk is offline shawnk  United States
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Hi Perry

The bad channel is Orange/Black
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Old 13th July 2010, 04:13 PM   #14
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What is the resistance between the blue wire and pin 5 of the op-amp for the orange channel?
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Old 13th July 2010, 04:40 PM   #15
shawnk is offline shawnk  United States
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0 ohm
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Old 13th July 2010, 04:42 PM   #16
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There's a long trace that zig-zags on the bottom of the board near the outputs for the orange channel. Is that trace burned?
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Old 13th July 2010, 05:04 PM   #17
shawnk is offline shawnk  United States
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All traces appear to be ok. The Orange/Black output is the fets to the left in this picture.

Click the image to open in full size.
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Old 13th July 2010, 05:07 PM   #18
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The over-current protection has been disabled so there's no way for it to bur those traces.

Check all of the following for the distorted channel.

Confirm that you have positive rail voltage on half of the outputs and negative rail voltage on the other half of the outputs.

Confirm that the resistors between the large driver transistors are within tolerance.

Confirm that there are no bad solder joints on the outputs.
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Old 13th July 2010, 05:45 PM   #19
shawnk is offline shawnk  United States
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There is pos & neg rail voltage for all of the corresponding fets ~46v

The resistors for the drivers are fine

I've double checked all of the solder joints and everything seems to be fine.


It's definitely something to do with the biasing circuit... if I measure voltage at the gate for the fets, it doesn't change when I adjust the pot. The three other good channels will vary voltage at the fet's gate when adjusting the pot. I hope that made some sense anyway.....

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Old 13th July 2010, 05:47 PM   #20
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Zeners?
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