Sundown SAZ3500 -DC on output - diyAudio
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Old 28th February 2013, 02:42 AM   #1
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Default Sundown SAZ3500 -DC on output

The amp has the sine wave riding on a negative 5V dc level. Does that sound like a leaky fet, I have pulled them and checked each one and found nothing out of the ordinary.

I have never run across this issue.
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Old 28th February 2013, 12:55 PM   #2
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Post a photo of the board (overall) and one of the driver board that they're using.
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Old 28th February 2013, 01:23 PM   #3
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They are using the dwm3640 with a piece of aluminum used as a heatsink. FQA24n50 output fets, 4 upper 4 lower per bank.

I wonder if a driver is messed up.
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Old 28th February 2013, 01:28 PM   #4
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Pin 9 on the driver board is+5v, 10 is input, 11 is ground, 12 is -5v. With the black probe on 11 and the red probe on 10, what is the DC voltage?
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Old 1st March 2013, 01:19 AM   #5
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pin 10 has -4VDC, hmm.
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Old 1st March 2013, 01:32 AM   #6
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Is there a 6.8k resistor feeding pin 10? If so, is the DC voltage on the driver board side of that resistor greater than the voltage (farther from 0v) on the other side of that resistor.
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Old 1st March 2013, 01:46 AM   #7
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Quote:
Originally Posted by Perry Babin View Post
Is there a 6.8k resistor feeding pin 10? If so, is the DC voltage on the driver board side of that resistor greater than the voltage (farther from 0v) on the other side of that resistor.
Yes it ties to a 6.8K resistor. The voltage on the driver side seems more stable, if that makes any sense. If I try to apply a full 12VDC to B+ the amp starts to draw excessive current. I only have one output fet per bank populated.

<Edit>
I removed the output fets and now unable to reproduce the negative voltage on that pin.
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Last edited by brandes.cm; 1st March 2013 at 01:59 AM.
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Old 1st March 2013, 09:27 PM   #8
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Was any work done to the amp previously or was the original problem -5v on the speaker terminals?
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Old 1st March 2013, 09:48 PM   #9
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That is how I received it. The output waveform riding on -5V.
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Old 1st March 2013, 10:58 PM   #10
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I would suspect the TL072 on the driver board.
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