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msaywitz  
#1 Posted : Thursday, December 9, 2010 8:54:39 PM(UTC)
msaywitz

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I am building a Placid 2.0, using the Avel 15VA 9+9 transformer, with the primaries wired in parallel and one pair of secondaries (black and red) connected to the terminals. The secondaries measure around 10.5 VAC. I finished populating the board, set VR2 and VR4 as described in the manual, and powered up the board with no load, The green LEDs light up and there is no smoke. However, the output is 10.5 VDC and changing the resistance on VR4 does not change the output voltage more than +/- .5 VDC. The measured VDC across R17 started at around .385 VDC and I was able to easily change it to .350 VDC using VR2. It does not appear that VR4 is damaged because when the power is off I can change the resistance all the way from single digits to 9.5k ohms. One other thing. When powered up, the heatsink attached to QN1 became hot, while the heatsink attached to QP1 staysl cold.

I checked and I did not mix up QN1 and QP1, and all of the parts look like they are in the right place. I can resolder all of the connections to cure any cold joints, but I thought that maybe you might be able to point me in a specific direction.
msaywitz attached the following image(s):
Placid 1.jpg (57kb) downloaded 98 time(s).
Placid 2.jpg (52kb) downloaded 97 time(s).

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Russ White  
#2 Posted : Friday, December 10, 2010 4:51:54 AM(UTC)
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Pictures could help.

Check the voltage at *both* inputs of the opamp as well as the output.
msaywitz  
#3 Posted : Friday, December 10, 2010 11:25:59 AM(UTC)
msaywitz

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Russ,

I added pictures to my initial post. Let me know if you need more.

Voltage at pin 2 (-IN) is 10.5 VDC
Voltage at pin 3 (+IN) is 11.5 VDC
Voltage at pin 6 (OUT) is 6.6 VDC

Voltage at output of board is 11.2 VDC

I last night I went over all of the connections with the iron and solder, to no effect.

I also built a LCDPS and it seems to be fine, I was able to adjust the voltage up and down as desired.
christensenleif@msn.com  
#4 Posted : Friday, December 10, 2010 1:04:51 PM(UTC)
christensenleif@msn.com

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why is C4 open?
best
Leif
Norway
msaywitz  
#5 Posted : Friday, December 10, 2010 1:47:50 PM(UTC)
msaywitz

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This is a 2.0 version of the Placid. I purchased it in May but ended up waiting until now to build it. There were no parts included in my kit for C4 and R7, and the 2.0a manual in on the website states, "Note that R7 and C4 are not normally used nor recommended.".
Russ White  
#6 Posted : Friday, December 10, 2010 4:54:37 PM(UTC)
Russ White

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It appears to me that the op amp is in backward.
msaywitz  
#7 Posted : Friday, December 10, 2010 7:10:34 PM(UTC)
msaywitz

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Russ,

Despite my initial assertions to the contrary, it does appear that way. Oh well, I guess the silver lining is that I get to practice my desoldering technique. Thank you.
Russ White  
#8 Posted : Friday, December 10, 2010 7:23:02 PM(UTC)
Russ White

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No worries mate, happens to us all from time to time. Please let us know if it is resolved after you set the op amp right.
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