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Hi Guys I have a Placid HD BP which when measuring the current without load can fluctuate up to 10 mv. The other thing i noticed was when adjusting VR it would increase/decrease significantly, for example a single degree/tiny rotation could be +/- 20mv or more. Pot issue perhaps? In the past i believe i have probably over rotated so it would not be surprise. Edited by user Sunday, March 22, 2015 10:47:50 AM(UTC)
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That is propably the issue. I've seen it before on a few Placids without even having over rotated them. IMO Fixed resistors are a much better choice when you're done testing.
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Double checked my work last night, QN9 was the wrong way around and after rectifying this the rise/fall is still somewhat there. Current observations with an ivy connected can change up to +/- 3mv. Could QN9 have caused any permanent damage? Should i still be looking at the trim pots as root cause? Edited at by user Saturday, April 4, 2015 3:24:00 AM(UTC)
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Assuming it's the version 2.1, just where is QN9. In my schematics, it's nowhere. Neither can I see it in the BOM.
However I can see it in the version 1.0
+-3mv leads me to ask, what are you using for measuring ?
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Originally Posted by: avr300  Assuming it's the version 2.1, just where is QN9. In my schematics, it's nowhere. Neither can I see it in the BOM.
However I can see it in the version 1.0
+-3mv leads me to ask, what are you using for measuring ? 1. I have version 1.0 2. TP VIN and TP CCS To give a more accurate description of the symptoms after redoing QN9 it is this: 1. All trim pots are very overreactive and unpredictable 2. When not changing any of the trimpots, the current output generally rises in increments of .1mv. So it may rise for say 1.0mv and then decrease a couple .1mv and then rise again after that. Should the current always remain stable down to .1mv?
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Which instrument (DMM) are you using?
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Before retiring this is how my 1.0 ended up. All pots replaced by fixed resistors. avr300 attached the following image(s):  cut.jpg (57kb) downloaded 15 time(s). cut2.jpg (91kb) downloaded 11 time(s).You cannot view/download attachments. Try to login or register.
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Originally Posted by: avr300 Before retiring this is how my 1.0 ended up.
All pots replaced by fixed resistors.
Its cheap, around $50 Digitech i think it was. I questioned the DMM as well and replaced the 9v battery inside it with the same result.
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You're talking about 1mv down to .1mv. 1/1,000v to 1/10,000v. I wouldn't care. I think your Placid is absolutely fine. Though I remember the 1.0 being a little touchy regarding the trim. That's why i replaced the pots. If you want a more reliable version, the 2.1 is dial-in-and-forget. Edited by user Saturday, April 4, 2015 8:46:41 AM(UTC)
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Originally Posted by: feckie
1. I have version 1.0
...
Should the current always remain stable down to .1mv?
No, and it's not a problem. If you're talking about the voltage (mV): there's always some drift due to the heat. If you mean the current (mA): these are shunt regulators. This means all current not being used is shunted as heat. You'll never notice a difference in performance even with a much bigger swing in current.
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