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Placid BP negative rail going nuts... +/- 30mV non stop...!
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pinnocchio  
#1 Posted : Tuesday, January 18, 2011 6:53:38 PM(UTC)
pinnocchio

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Hi,

The negative rail is going up and down non-stop about +/- 30mV and sometimes stays put for a few seconds... The mA on both rails are perfectly set. Positive rail stays put without issue.

Do you know what it could be?

Thanks
Do

Edited by user Tuesday, January 18, 2011 6:54:59 PM(UTC)  | Reason: Not specified
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Russ White  
#2 Posted : Tuesday, January 18, 2011 9:42:27 PM(UTC)
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This is a new one on me. :) Only thing I can think of is possibly an issue with the pot that sets the voltage gain, or maybe a solder joint, or possibly an issue with the reference voltage. I would check all of those. It is normal for the voltage to fluctuate a little with temperature changes but not very quickly.
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pinnocchio  
#3 Posted : Wednesday, January 19, 2011 8:38:58 AM(UTC)
pinnocchio

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I think I'll start by changing the pot and look for bad solder join.

When the Placid is warmer, it seems to stop.

Let me double check everything and let you know the outcome.

Thanks
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Brian Donegan  
#4 Posted : Wednesday, January 19, 2011 8:47:22 AM(UTC)
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pinnocchio wrote:
When the Placid is warmer, it seems to stop.


That would tend to indicate a bad (cold) solder joint.
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pinnocchio  
#5 Posted : Friday, January 21, 2011 12:04:18 AM(UTC)
pinnocchio

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I think I'm dealing with some kind of oscillation here... Usually when components get hotter they sometimes settle which is my case right now. A cold solder join would not make the circuit go up and down +/- 30mV, it would just fail then when hot work or the opposite. Could also be a defective pot but I'm skeptic.

I don't have a scope so I'm cooked right now... I might bring it to one of my engineer friends at Simaudio for a quick checkup if they have time.

I did check for cold solder join anyways but couldn't find anything wrong. Maybe I'll pass the soldering Iron on all components on the negative rail and see what happens afterward.

Thanks
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