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Joined: 11/9/2012(UTC) Posts: 1  Location: Bordeaux
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Hi everyone,
Seems that i was a problem with my LCDPS power supply. This one is currently hook up to a Buffalo III board, and everything went just fine until today : end of christmas, no more lights on the Trident regulators.
At first, i thought that it was the DAC that stopped working since i have a perfect 5,25V output on both stage of the LCDPS. So i change the Buffalo board for another one, but came with the same result : no lights.
Then i tried to hook-up another linear power supply on both of my Buffalo III, and lights were on all over the boards. What a relief! Still, i don't understand what is happening with the LCDPS since it gives me the right voltage at the output, and i see no trace of burn or anything.
Is that possible that the LCDPS is suddenly unable to power a Buffalo III despite the fact that it give the right voltage at the output. What can be the cause(s) of such mystery?
Thanks!
Regards
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Rank: Member
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Joined: 4/21/2007(UTC)
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My LCDPS worked great for a long time but is now failing. 9v in, 7.5 volts out to four Opus boards. The VD side maintains 7.5v but the VA side has been slowly dropping. Without full voltage, my DACs were picking up AM radio!  But now VA is down to 6.3v and DAC output is nothing but static. Any suggestions? Better to attempt repairs or replace with a larger PS? Cheers, Frank
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The circuit is pretty simple. and the schematic is available.
There is not much to go wrong... Check that you don't have any dry joints or solder whiskers. Make sure you are still getting good power from your transformer.
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Originally Posted by: Russ White  Make sure you are still getting good power from your transformer. Thanks Russ. I don't know anything about what can go wrong with transformers that would cause gradual power loss. I'm supplying 4 opus boards using the 9+9v 15VA toroid from you guys, so the rated current per side is .83 A. Here is what I'm finding: a) Either secondary of the transformer alone, connected to the VA side of the LCDPS, supplied the Opus boards at a full 7.5v (drawing 660 mA for the four boards combined). b) If I add the transformer's other secondary to the VD side of the LCDPS the VD output is exactly 7.5v - but then the VA output voltage drops from 7.5 to 6.3v. No heat, smoke, or light from anything... This condition developed over the course of at least 100 hours of use. Transformer??? [ if so, replace with another 15VA or go larger?] Best regards, Frank y'know... I COULD play 'musical chairs' with power supplies in this 8 channel DAC chassis... Would shunt-regulated power improve the Opus' 8741 performance? I COULD move the older LCDPS to the one Buffalo-2/trident-3 board (but only if it still sounded amazing). Then I could use the free Placid 2.1 for combined Opus VD, and squeeze in a new Placid HD for Opus VA. Assuming the voltage/current issues are sorted out, would this be fundamentally better?  Edited by user Sunday, January 13, 2013 6:09:01 PM(UTC)
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Rank: Member
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Joined: 4/21/2007(UTC)
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Location: Minnesota
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Originally Posted by: Russ White The circuit is pretty simple. and the schematic is available.
There is not much to go wrong... Check that you don't have any dry joints or solder whiskers. Make sure you are still getting good power from your transformer. This is getting weird: New 9V AC power transformer into the LCDPS gives solid 7.5 volts output into 4 Opus boards. BUT THEN ... I power up the computer that powers the 8 channel I2S interface board. VA drops immediately from 7.5 to 7.1 until midway through boot sequence, at which time voltage drops to 6.5. BUT FINALLY ... I fire up the Placids that power only the Buffalo and Legato in the same chassis... With no connection to the other circuits whatsoever, VA immediately drops to 6.1. The only (intentional) connections between any of the TPA boards and the interface board is I2S, stolen from vias. The Buffalo DAC still locks and plays from this I2S source. Any ideas, anybody?  Frank Edited by user Sunday, February 3, 2013 3:06:28 PM(UTC)
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Sounds like something is drawing too much current - or at least more than the PS is setup to source.
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As the DACs (and output stages) begin to process signals, they will draw more current.
I would try disconnecting the Opus DACs one at a time, until you see the voltage go back to 7.5V. This will isolate what may be a problem DAC module.
If each can be removed and no changes are seen, that points to the PSU or transformer.
It could be something like a failing cap on the PSU or a DAC module.
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