PSU Problem with Placid BP and BII

tubeing · 12th June 2011, 06:05 PM

Hi to everyone,
I've got my boards from TP some months ago, but I had some time to work on them only last week. Today I set up Placid and Placid BP as explained in the manual and all was ok. I connected +5V from Placid to the BII board and everything was ok. Then I connected +/-12 from Placid BP to Legato board and...something went wrong. -12 remains at -12V while +12 went down to about 3V. I switched off immediatly the power but it was too late. Now my positive rail (without load) can reach only 11V max, and I can't see any voltage drop across R2. I measured VR2 and found about 4Mohm , so probably VR2 has gone...Maybe also Q1...I've checked the legato board and there are no shorts between +V and GND...Any suggestion to make things alive again will be appreciated.

Thanks
Stefano

Russ White · 13th June 2011, 12:12 PM

Placid and Placid BP are shunt regulated supplies, so a dead short at output should not be fatal because the current is limited.

Do all of the LEDs light correctly on the Placid BP?

My suggestion would to isolate and test the placid BP on its own. Try simply replacing VR2 first. VR2 might have been damaged by adjusting too far past the stops.

tubeing · 13th June 2011, 04:06 PM

Thanks Russ.
The leds are working, I have a new trimmer to replace the old one.
Now, if the placid will work well with the new component, I need to find out the problem that caused this situation...legato?
Thanks again.
Stefano

Russ White · 14th June 2011, 01:48 PM

Most likely just a damaged pot.

tubeing · 18th June 2011, 01:53 PM

Hi Russ,
I've changed the trimmer but with the new one I can only reach about 150mA through R2. Even with VR2 set to the min...I think that also QP1 has been damaged...and I don't find anything else in the board or in the legato board that can give me some clue on what it's going on.
Thanks.
Stefano

tubeing · 02:45 PM

Some news (bad news): after about 20 min after power on (Irs = 150mA), the Vout went to about 20V (the rectified voltage after the bridge)...with Placid BP disconnected from everything. QP1 is cold, QN3 is very hot, D5 is "off" while D1 e D2 "on". I think I have a complete set of problems...not only one

Then, I have to set VR2 near the max to allow Vout to go down to 12V. I this case, both VR2 and VR4 set the Vout. When I set Ir2 to less than about 20mA D5 starts to emit light again but Vout is about 18.4V. Any suggestion?
Thanks
Stefano

12th June 2011, 06:05 PM	#1
tubeing diyAudio Member Join Date: Nov 2009	PSU Problem with Placid BP and BII Hi to everyone, I've got my boards from TP some months ago, but I had some time to work on them only last week. Today I set up Placid and Placid BP as explained in the manual and all was ok. I connected +5V from Placid to the BII board and everything was ok. Then I connected +/-12 from Placid BP to Legato board and...something went wrong. -12 remains at -12V while +12 went down to about 3V. I switched off immediatly the power but it was too late. Now my positive rail (without load) can reach only 11V max, and I can't see any voltage drop across R2. I measured VR2 and found about 4Mohm , so probably VR2 has gone...Maybe also Q1...I've checked the legato board and there are no shorts between +V and GND...Any suggestion to make things alive again will be appreciated. Thanks Stefano

13th June 2011, 12:12 PM	#2
Russ White diyAudio Member Join Date: Jan 2005 Location: Nashville, TN, USA	Placid and Placid BP are shunt regulated supplies, so a dead short at output should not be fatal because the current is limited. Do all of the LEDs light correctly on the Placid BP? My suggestion would to isolate and test the placid BP on its own. Try simply replacing VR2 first. VR2 might have been damaged by adjusting too far past the stops. __________________ Less pulp more juice Twisted Pear Audio.

14th June 2011, 01:48 PM	#4
Russ White diyAudio Member Join Date: Jan 2005 Location: Nashville, TN, USA	Most likely just a damaged pot. __________________ Less pulp more juice Twisted Pear Audio.

18th June 2011, 02:32 PM	#6
tubeing diyAudio Member Join Date: Nov 2009	Some news (bad news): after about 20 min after power on (Irs = 150mA), the Vout went to about 20V (the rectified voltage after the bridge)...with Placid BP disconnected from everything. QP1 is cold, QN3 is very hot, D5 is "off" while D1 e D2 "on". I think I have a complete set of problems...not only one Then, I have to set VR2 near the max to allow Vout to go down to 12V. I this case, both VR2 and VR4 set the Vout. When I set Ir2 to less than about 20mA D5 starts to emit light again but Vout is about 18.4V. Any suggestion? Thanks Stefano Last edited by tubeing; 18th June 2011 at 02:45 PM.

Thread Tools	Search this Thread
Show Printable Version Email this Page	Search this Thread: Advanced Search

13th June 2011, 04:06 PM	#3
tubeing diyAudio Member Join Date: Nov 2009	Thanks Russ. The leds are working, I have a new trimmer to replace the old one. Now, if the placid will work well with the new component, I need to find out the problem that caused this situation...legato? Thanks again. Stefano

18th June 2011, 01:53 PM	#5
tubeing diyAudio Member Join Date: Nov 2009	Hi Russ, I've changed the trimmer but with the new one I can only reach about 150mA through R2. Even with VR2 set to the min...I think that also QP1 has been damaged...and I don't find anything else in the board or in the legato board that can give me some clue on what it's going on. Thanks. Stefano

Similar Threads
Thread	Thread Starter	Forum	Replies	Last Post
Placid-BP Bipolar Shunt Regulated Power Supply	Russ White	Twisted Pear	176	18th April 2013 06:32 AM
FS: Buffalo II DAC + Placid Combo, Legato I/V Stage, 2x Placid BP Modules	damohpi	Swap Meet	4	23rd November 2010 08:51 AM
FS Twisted Pear Placid BP shunt regulator	merlin el mago	Swap Meet	8	1st April 2010 11:17 AM
CCS in Placid-BP Bipolar Shunt Regulated Power Supply	Allen Wright	Power Supplies	25	21st November 2009 07:41 PM

New To Site?	Need Help?
Register to Participate Search Privacy Statement Contact Us	Frequently Asked Questions Did you forget your password? Mark Forums Read