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Placid 2.0.1 shunted current slowly reduces to zero powering BII + Tridents.
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fred_com  
#1 Posted : Thursday, February 3, 2011 10:29:08 AM(UTC)
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Hey guys!

Got a little problem with my Placid after installing Tridents on BII.
To provide Tridents with needed current, I did as Russ suggested and shorted R5 (didn't have 4.7R handy), adjusted VR1 to provide ~520 mA
System started without a glitch, all was fine, music is wonderful, shunted current was about 60mA. Then, after listening for about 5-6 hours, I've checked shunted current on a Placid, and it was something like 4-5mA. So I adjusted it again to 60mA. On the next day on powerup the shunted current was about 120mA (figures) so I turned it down to 60 again, and after some time it began to reduce again.

Things I've tried:
1) removed short on R5 and put in 220Ohm trimpot. It helped me to reach ~50mA, but didn't solve the problem.
2) used fixed 220 Ohm resistor in place of VR1, still no dice.
3) used USSR military spec 0.1% 240 ohm resistor - result is the same.

After all this it occured to me that current setting resistor is not the problem d'oh!

So the question is this - what are my options? What can I check?

Thanks,
Fedor

P.S. Just checked the output voltage, it swings from 5.41 to 5.6 could this be a problem?

Edited by user Thursday, February 3, 2011 10:35:43 AM(UTC)  | Reason: Not specified
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Russ White  
#2 Posted : Thursday, February 3, 2011 12:12:20 PM(UTC)
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Honestly your really pushing the placid harder than it was really intended to go. My guess is it is getting too hot. You may need to use larger heat-sinks.
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Russ White  
#3 Posted : Thursday, February 3, 2011 12:19:02 PM(UTC)
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Also it is normal for both the current and the VREF to drop a bit as the Placid warms up. This is because of the temp coefficient of the LED and the transistors. So What I usually do is make sure that the voltage at low temp (startup) is never more than the max voltage input for the target, because I know that as the placid heats up the output voltage will lower a bit.
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fred_com  
#4 Posted : Thursday, February 3, 2011 2:45:39 PM(UTC)
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Hi Russ, thank you for a quick answer!

I was worried about temperature too, so today it was working with the lid off the case, and at the end of the day heatsinks were not really hot (judging by the finger thermometer :)), I'd say 50-60 degrees Celsius (122-140 Fahrenheit).
I guess I'll try to run it without the Tridents on the weekend, to better isolate the problem (I'm thinking maybe this was happening even before the Tridents, just that I haven't noticed that).
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Russ White  
#5 Posted : Thursday, February 3, 2011 3:45:48 PM(UTC)
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Well you wouldn't need nearly so much current without the Tridents. It not the tridents themselves that are the cause of your symptoms, it the extreme amount of current through the placid.
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fred_com  
#6 Posted : Friday, February 4, 2011 10:51:42 AM(UTC)
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Hi Russ, I see your point.

So I guess only option for me is getting a LCDPS, right?
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avr300  
#7 Posted : Friday, February 4, 2011 1:47:51 PM(UTC)
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Which trafo are your using in front of the Placid ?
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fred_com  
#8 Posted : Friday, February 4, 2011 2:38:13 PM(UTC)
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Avr300, you're right on the money! Looks like my trafo is failing or something... I was measuring shunted current today, when my wife turned on the electric teapot (2kW). And I saw a drop in a shunting current for about 10 mA. So this is definetely the trafo.
It's an R-type chinese one, with four secondaries, two 9V and two 12V, providing 850mA (or so the label says).

Russ, I really want to apologise for having doubted the Placid and for being somewhat a PITA :)

Well, got to go find myself another trafo.
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