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Problems with LEDs not lighting up and no current adjustment
Rank: Member
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Location: Toronto, Ontario, Canada
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Hi guys, I've just finished building building both the Placid and Placid BP which I received about 6 months ago, and both are suffering the same issues - the LEDs are not lighting up and while I can adjust the voltage output (a little tricky as it jumps around a lot), I cannot adjust the shunt current. I'm quite a proficient builder and I've doubled checked all parts to be populated correctly. I have attached photos of both the builds. Any ideas? Suggestions for debugging? Anything? Thanks    
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This sounds like misplaced transistors.
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Just verified QN1&3/QP1&3 to be correctly populated.
The unexpected result is very strange as I've went through the board with a fine-tooth comb and doubled checked all parts placements, including re-measuring every resistor (had to assume on the 1R are correct as my DMM isn't that great).
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Rank: Administration
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Rank: Member
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Q2: PN4393
QP2: BC560
QP1: BC550
QP2: BC560
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Did you check that you do not have a reversed LED?
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Rank: Member
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You know, I've double check those many times, but how could I be so foolish, I did install them backwards! All 8 of them between the 2 boards! Funny thing is that I was certain in my mind the anode was the flat portion of the symbol (which is also drawn in reverse on the board from what I thought in my mind).
I just reversed the LEDs on the single-supply and it fired up as expected. Now on to delicately removing the 6 off the split supply.
Thanks for the debugging help, much appreciated!
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Rank: Member
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Just reversed all of the LEDs, went through the setup instructions and everything seems to be running perfectly.
Thanks guys!
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I'm pretty sure I've managed to do the same thing. I'm measuring 18.4v on the transformer to Placid inputs and 24v on the placid outputs and cannot adjust the output voltage. Before I go changing all of the LED's does this sound right? stewart attached the following image(s):  IMG_20110423_192046.jpg (133kb) downloaded 299 time(s).You cannot view/download attachments. Try to login or register.
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Take a sideways look into the LED's. Their orientation are like this, flat side to - Edited by user Sunday, April 24, 2011 12:52:07 AM(UTC)
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Yes, look for the flat edge in the LED and match with the flat edge on the PCB silk screen. :)
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Thank you they were all reversed. I have one rail working without issue however one of the LED's(pictured below) lights up very breifly when first powering on but then remains off. This rail still reads 24v on the output. One of the pads lifted a little bit when I was resoldering however not significantly. Is it possible I destroyed the trace? Edited by user Sunday, April 24, 2011 12:34:57 PM(UTC)
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Bottom trace looks ok. You could clean it up a little. How's conditions of the top trace belonging to this leg ? Edited by user Sunday, April 24, 2011 2:21:11 PM(UTC)
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Check that the top trace has a good solder joint to the LED. Also check the voltage across C3.
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I will check the top trace. I get 1V across C3 on the non working side and 2V on C4.
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Then it sounds like that LED is either damaged, or QN1 is possibly damaged/dead. I would replace that LED and hope that's all it is.
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Unfortunately after trying a new LED no luck getting it to light up. Short of replacing QN1 is there a way to measure to make sure that is the culprit? Thanks.
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Rank: Advanced Member
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Rank: Administration
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I believe I already answered you. :) I would next try a new transistor.
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Rank: Advanced Member
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I just received a replacement for QN1 from Mouser. Before I install it I wanted to double check as the part is labelled slightly differently from the one I removed. I ordered 512-FJPF5200OTU as indicated in the BOM.
The part I received reads
F1A50AA
J5200
R
whereas the original reads
F1 J32
J5200
O
Is this a suitable replacement? Thanks for the help.
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Problems with LEDs not lighting up and no current adjustment
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