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The Placid (non-bipolar) seems to be working, the output voltage seems to be correct -- but adjusting VR1 has no effect on the V across R8: it is constant at -0.493V (yes, negative). Edit: the polarity of the resistor seems to matter. I'm confused. Further, the constant V is variable, seemingly determined by temperature, which I think is fine. Lastly, there seem to be no stops on VR1: perhaps I have simply turned it too far one way for a difference to be noticed? Edit 2: R1 shows a resistance of 0.214 kohms if I turn clockwise (the word Placid at the bottom). What have I done? I'm assuming that the voltage should be positive and that changing VR1 should affect R8. So close! Edited by user Wednesday, August 11, 2010 11:16:51 PM(UTC)
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Adjusting VR1 should indeed change the current through R8. Make sure the when you carefully turn VR1 in both directions it changes the resistance. If it won't adjust then it is possible you turned it past it the stops and you will need to replace it. The voltage across R8 will be either positive or negative depending on the way you arrange your DMM leads. Edited by user Thursday, August 12, 2010 8:01:32 AM(UTC)
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Russ White wrote:Adjusting VR1 should indeed change the current through R8.
Make sure the when you carefully turn VR1 in both directions it changes the resistance. It used to do this: I had set the Placid to the correct resistance before I applied power. Which means... Russ White wrote:If it won't adjust then it is possible you turned it past it the stops and you will need to replace it. Rats! I suppose I'll need another, then. I'm not really sure how I managed to break the trimpot, as I was fairly careful and do not recall hitting a stop. Still, these things will happen. May I order another from you or would you like me to use some other means? Russ White wrote:The voltage across R8 will be either positive or negative depending on the way you arrange your DMM leads. Yes, I was confusing voltage with resistance. I blame the fact that I was SO CLOSE to having a working DAC, then blew it. Out of curiosity, is the amount of current being put out by the Placid too great for the Buffalo II or can I use it? If not, I shall have to buy a wall-wart for use until I can fix the PSU (after all, there's that meet on Saturday). |
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Its should actually work fine as long as the placid heatsinks are not getting too hot. Mouser carries the pots, and they are pretty inexpensive. You can order a new one from them. Edited by user Thursday, August 12, 2010 11:49:54 AM(UTC)
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