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Old 20th October 2009, 03:38 PM   #1
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Default lm3886 - dc on output

Hi

Bought one of them cheapy's off fleabay.

Problem is that one channel works....and very well at that, other channel has 35v dc on the output. Should have checked before I connected speaker.

Any ideas or is it as simple as chip doa.

Wizard
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Old 20th October 2009, 10:41 PM   #2
Minion is offline Minion  Canada
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Location: Cowican Bay , vancouver island
Check that you have connected the PSU to the Chip amp correctly and that you are getting the correct voltages at the Power pins of the LM3886 , usually if there is that much DC at the output it is because the chip isn"t getting power on one of the Rails ....

Good luck
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Old 21st October 2009, 05:52 AM   #3
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Thanks Minion

Checked the voltages and strangely got 35V between pins 9 and 10. Should this not be 70V. Other than that all seems to measure out ok.

The beast in question is the following.

Click the image to open in full size.
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Old 21st October 2009, 08:50 AM   #4
rem280 is offline rem280  United States
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Pins 9 and 10 are Vin+ and Vin- not V+ and V- you should mesure no voltage between the two. The difference between these pins will be amplified by how ever much gain the amplifier has and move the output to just the positive or negative rail. You need to figure out what the cause of this voltage is I don't have a schematic for your amp and your picture isn't working so Im not sure what to check first but it sounds like there is a short to power somewhere or something hooked up wrong.
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Old 24th October 2009, 06:54 AM   #5
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Just a quick update on voltages.

Pin1 to ground +36.2
Pin4 to ground -36.1
Pin3 to ground +34.6
Pin9 to ground +34.1
Pin3 to Pin5 +1.4v

Any ideas. I am assuming the chip is fried as there is virtually full +ve supply on the input pin with the exception of the 1.4v between pin3 and +ve rail
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