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About two years ago I assembled a Buffalo III Dual Mono using Legatos, and then current Placid Power Supplies. My Buffalo III Dual Mono has worked well since it was first assembled.
This past spring, I decided to upgrade to Version 2.1 of the Placid Power supplies and just got around to building them a few weeks ago. The Placid HD-BP Version 2.1 supplies installed in my system easily and are quite easy to calibrate. After repeated attempts, I have not been able to get the new Placid HD supplies to work at all. With no load, I cannot get the voltage any lower than about 5 v., however, I'm able to set the shunt current to whatever I want. Under load (just a Buffalo III board) the voltage drops to ~1.0 v. and the shunt current reads 0.0 v. No amount of adjustment of VR1a or VR2a causes any effect. These findings apply to both of the new Placid HDs I have.
I find it difficult to believe that I have wired something wrong, since I have repeatedly checked the parts during and after assembly and both Placid HD boards exhibit the same problem. In addition, both the + and - sides of the Placid HD-BP boards appear to work without difficulty.
I note recently that the recommended value for R8a has been changed from 470R to 220R, a change that I made without any effect.
I would be very grateful for your help. Thanks!
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Im sure we can get it running. Can you post a couple of pictures.
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I have some pictures, but after many attempts, I have not been able to post them. Could someone explain how it is done? Thanks! eseal attached the following image(s):  DSC02490a.jpg (121kb) downloaded 19 time(s). DSC02492a.jpg (104kb) downloaded 22 time(s). DSC02491a.jpg (132kb) downloaded 17 time(s). DSC02493a.jpg (106kb) downloaded 23 time(s).You cannot view/download attachments. Try to login or register.
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On an existing post use the attach button.
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Photos attached above. Thanks very much avr300 and Brian!
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Hi Eseal,
I also jumped from the old version Power Supply to the new version and wonderwell I also had difficulties somehow.
I exidentally placed one capacitor the wrong way around.
But for as far I can see you have placed them correctly.
I also was unable to adjust the currents at higher loads.
AVR300 helped me a lot so since he is offline maybe I can give you a head start.
Important to know if the TP_VREV shows the correct value to ground.
I'm not sure of the correct value. For my HDBP it was 2,5 V but I see it must be around 4.0 VDC in the schematic.
But just measure and someone can tell you you it is the correct value or not.
And a tip from my own experience:
Grap a loop and check if there is no tiny Tin Bridge interconnecting the legs of the Voltage Requlators!
Good luck!
Jordo
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Measure voltage between TP_VREF+ and GND.
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Thanks very much avr300 and Jordo.
The measured voltage between TP_VREF and GND is as follows:
Board A: 2.483 V.
Board B: 2.479 V.
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Ok and do you found any Tin spillage bridges between the voltage regualtors' Legs?. And speaking of those; are they all in the correct position? Haven't you swapped them accidentally? Edited by user Thursday, January 29, 2015 10:35:11 PM(UTC)
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Hi Jordo,
There are no solder bridges between the legs of the Darlingtons and not is not possible to incorrectly swap them because both are the same part (both are MJF122G).
Still trying to figure out why I'm having trouble with the Placid HDs, but not the Placid HD-BPs.
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Offcourse, it's a non BP board.  Euhm hm, there stops where I can help I guess... Checked the p/n's of the Voltage regulators with the BOM? Also checked the resistors? I hope you'll find it soon! Good luck! Jordo
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Hi Jordo,
I appreciate your trying to help.
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Originally Posted by: eseal  Thanks very much avr300 and Jordo.
The measured voltage between TP_VREF and GND is as follows:
Board A: 2.483 V.
Board B: 2.479 V.
Great. That's good. - Do check that the REF1 is the LT1034 and not mixed up with the transistors (all in TO-92 house) Your soldering looks fishy. Are you sure these are good contacts. It might just be the picture quality that lacks. What happens is you (unconnected) dial it in to 5.2v @ output and set it to shunt 550mA (measure 0.55v across R2) power down, connect the Buffalo and then power-up the thing? avr300 attached the following image(s): cut.jpg (65kb) downloaded 17 time(s).You cannot view/download attachments. Try to login or register.
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"Even a blind squirrel occasionally finds a nut"
Success!
As I thought more about this problem, I wondered why the voltage and current without a load could be adjusted easily, but that voltage went to ~1 V and current went to 0.00 mA when either board (but not both) was connected to a load. Then it occurred to me that both buffalo IIIs might be drawing current, which would cause too great a demand on a single power supply. So, I connected both boards simultaneously for final calibration of voltage and current under load. I had no difficulty performing the final voltage and current calibration under load when BOTH placid HD Version 2.01. power supplies were connected to their respective Buffalo IIIs.
I have learned a valuable lesson from this. Apparently, in Dual Mono configuration, the Buffalo III boards are not as power supply isolated as I thought.
Many thanks to avr300, Jordo, and Brian to each for your help.
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