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I recently built the Dual Placid as an upgrade for my Buff32 that is using one LCDPS for the digital side and a LCBPS for the analog side. I wanted to replace the LCBPS with the Placid to better SNR on the audio.
I built the Placid and carefully set up (adjusted) the four pots to the prescribed voltages with the PS unloaded as directed by the manual. I left the Placid on for many hours to make sure it was stable before connecting it to the Buff32. When I made the connections and applied power the rail voltages from the Placid dropped to approx 1.5~1.7 volts. Adjustments to the output pots did very little. I put the LCBPS back and all is fine.
I am using the 30VA dual primary and secondary 15V transformer I purchased with the Placid. The placid is running cool so I can not figure what could be wrong.
any suggestions
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Rank: Administration
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Sounds like you have a short somewhere, probably something installed backwards. Can you post a picture of your Placid?
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Rank: Member
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Pardon my ignorance but I do not see how to post pictures I will email them to you
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This happened to me on one rail. I had soldered in the opamp backwards. The symptom was exactly the same. About 1.7 v on the output and no ability to adjust it. I was able to desolder the opamp and bought a new one from Mouser... watching the position more carefully this time. Edited by user Monday, November 2, 2009 4:11:11 PM(UTC)
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I sounds like you may not have had the CCS current adjusted high enough. What current to you adjust to?
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Rank: Member
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thanks
I sent photos to Brian and he gave me some ideas to check out.
I was able to adjust the voltage drop across the resistors to .25 volts as manual stated but this also dropped low when the PS was loaded
I still would like to know how to post photos
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Rank: Administration
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Joined: 10/24/2006(UTC)
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Click Attach on an existing post. It's kinda backwards.
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Rank: Member
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Location: Baltimore, MD USA
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thanks for the hit on the head Brian I NOW see the "attach" button
Its going to be fun trying to see if I mounted the transistors wrong with the Heat sinks in place. what I do not understand is why it tested okay with out load if I screwed up the transistor placement
I suppose the easiest way since I have noway to test transistors is to just order a new set and replace them all.
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Rank: Administration
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I think you will be able to see them. The tough one is QP2, but you can look through the gap at the bottom of QN1's heatsink to see the numbers on it.
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Rank: Member
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Well I confirmed the proper placement for the transistors and reheated all connections then cleaned the flux away and all seems fine. I was able to adjust voltage drop accross R17 and R18 to .25 volts and adjust VR3 and VR4 to get my +15 and -15VDC while buff32 was connected.
Thanks for all the help now to sit back and listen.
As a side note what would be a proper loading resistor on the Placid to simulate the Buff32 (Audio side)
Im guessing 220 ohm 10watts
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