hep, Parasound pfet 900II

yzriver · 12th December 2011, 01:05 AM

Hi,

My parasound PFET 900II preamp doesn't work recently. One channel has a distorded sound, and there no output from the other channel except some humming.

Can anyone have ideal how to check it, or find a schematic?

Thanks,

Jay

yzriver · 02:01 AM

I open the cover, and take some picture. I don't see any burned component. I can measure the regulator output +-25 and +-15.

I check the relay first. It locates at bottom center of the picture, and it is model KUAN HSI D2A12, assumed it requirs 12V to turn on. However there is about 5.9V measured. Is it something wrong there? I post there picture here. Can anyone guess the circuit beside it?

thanks,

john curl · 16th December 2011, 02:46 AM

Should be +/- 15V. Regulator is gone?

yzriver · 17th December 2011, 01:51 AM

Hi, John, Thanks for your reply.
The regulators are fine. I have +/-24V and +/-15V measured.
I found the problem is from the relay circuit. The relay is D2A12. I measure the voltage across the coil, one side is 11.93V, the other side is 5.55V, after I turn the machine on for a while. There is no change even I stay longer. Then I measure the resistance between the poles. One side is 0ohm, the other side is open. I believe there is something wrong in the relay circuit. So I short the poles by jumping wire for both side. Now music come out from both side.
I would like to solve this problem completely. The resistor have right value. The caps have no short. Is it possible those two transistors are gone?

thanks,

12th December 2011, 01:05 AM	#1
yzriver diyAudio Member Join Date: Aug 2008 Location: Boston, MA	hep, Parasound pfet 900II Hi, My parasound PFET 900II preamp doesn't work recently. One channel has a distorded sound, and there no output from the other channel except some humming. Can anyone have ideal how to check it, or find a schematic? Thanks, Jay

16th December 2011, 01:53 AM	#2
yzriver diyAudio Member Join Date: Aug 2008 Location: Boston, MA	I open the cover, and take some picture. I don't see any burned component. I can measure the regulator output +-25 and +-15. I check the relay first. It locates at bottom center of the picture, and it is model KUAN HSI D2A12, assumed it requirs 12V to turn on. However there is about 5.9V measured. Is it something wrong there? I post there picture here. Can anyone guess the circuit beside it? thanks, Last edited by yzriver; 16th December 2011 at 02:01 AM.

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16th December 2011, 02:46 AM	#3
john curl diyAudio Member Join Date: Jul 2003 Location: berkeley ca	Should be +/- 15V. Regulator is gone?

17th December 2011, 01:51 AM	#4
yzriver diyAudio Member Join Date: Aug 2008 Location: Boston, MA	Hi, John, Thanks for your reply. The regulators are fine. I have +/-24V and +/-15V measured. I found the problem is from the relay circuit. The relay is D2A12. I measure the voltage across the coil, one side is 11.93V, the other side is 5.55V, after I turn the machine on for a while. There is no change even I stay longer. Then I measure the resistance between the poles. One side is 0ohm, the other side is open. I believe there is something wrong in the relay circuit. So I short the poles by jumping wire for both side. Now music come out from both side. I would like to solve this problem completely. The resistor have right value. The caps have no short. Is it possible those two transistors are gone? thanks,

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