PS Diagnosis? - diyAudio
Go Back   Home > Forums > Amplifiers > Solid State

Solid State Talk all about solid state amplification.

Please consider donating to help us continue to serve you.

Ads on/off / Custom Title / More PMs / More album space / Advanced printing & mass image saving
Reply
 
Thread Tools Search this Thread
Old 31st October 2004, 06:34 PM   #1
sam9 is offline sam9  United States
diyAudio Member
 
sam9's Avatar
 
Join Date: Jun 2002
Location: Left Coast
Default PS Diagnosis?

Description of PS:
A standard unregulated power supply ~42-0-42 VDC under load. Uses 25A 600V bridge (with subbers), four Nichicon 10,000uF filter caps, followed by a pair of .1uF film caps, and a pair of 4.7kR bleed resistors. Transformer is A-L 35-0-35 500VA.

DC voltage measurements show everything to be just as desired and expected, no off set everthing steady whether under constant load or no load. BUT ( AC while voltage measured at the posative DC rail show nothing except perhaps a mV of ripple, at the negative rail I read a pulsing AC reading - the DMM cycles between 1-2Vac to 23Vac constantly. I suspect a bad filter cap that won't hold a charge, hence the rapid pulsing. But before I tear everything apart and start replacing caps can anyone confirm or refute my diagnosis.

Oh yes I have disconected the PS from the amp boards to isolate the problem. I did not check the AC at the rails before installing and connecting the amp boards. I actually discovered this by tracing back why the MOSFETs in the amp were getting too hot. The thermal switch on the back of one opened which was the first clue something was amiss.
  Reply With Quote
Old 31st October 2004, 07:28 PM   #2
Enzo is online now Enzo  United States
diyAudio Member
 
Join Date: Sep 2004
Location: Lansing, Michigan
Your output devices won't overheat because the power rails are hummy. You have disconnected the amp circuits, but is there anything else riding on those rails, no matter how seemingly innocent? Disconnect EVERYTHING from the power supply, even the LED power indicator.

SCope it to see what the ripple looks like. Beyond that, either the cap is leaky on that rail, or the rail is being loaded down. Isolate the problem. Swap the filter caps and see if the problem moves with them. If so, you have a bad one. If the caps are OK, then go back to basics. Remove the bleeder and film cap from the bad side. Then pull the snubbers off the bridge. If the bleeder is mismarked or if you inadvertently put in a wrong value or if the film cap is bad, there could be a load on the rail not present on the good side. Likewise a leaky snubber could be passing some AC on through past the bridge.

And check the bridge. If one leg is open, then you essentially have half wave and it will have more ripple.

I doubt it is the AC mains, that would affect both rails. Well, unless the power mains waveform was grossly assymetrical.
  Reply With Quote
Old 31st October 2004, 09:26 PM   #3
sam9 is offline sam9  United States
diyAudio Member
 
sam9's Avatar
 
Join Date: Jun 2002
Location: Left Coast
Thanks, you are confirming my approach but have a couple of additional suggestions.

One help I just remembered is that I built two identical power supplies, the second one for a follow on project. I've swaped them and No. 2 shows no problems so far. Once I've completly checked out No.2, I'll reconnect the amp PCBs. Then if all else is OK, I can come back to PS No.1 and figure out the problem at my leisure.
  Reply With Quote
Old 1st November 2004, 06:59 AM   #4
AndrewT is offline AndrewT  Scotland
diyAudio Member
 
Join Date: Jul 2004
Location: Scottish Borders
Hi,
your DC voltage is very low for a 35vac 500va transformer.
I would expect +-48 to 50.5v on the rails when loaded. How big is your load? When you have completed the caps checks, then check you have the same plus & minus Vrail voltages.
regards Andrew T.
  Reply With Quote

Reply


Hide this!Advertise here!
Thread Tools Search this Thread
Search this Thread:

Advanced Search

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off


Similar Threads
Thread Thread Starter Forum Replies Last Post
Faulty amp - diagnosis? Omega_Void Solid State 7 11th July 2008 10:52 AM
Sony CDP-H3600 diagnosis help raymondjiii Digital Source 0 1st May 2007 09:26 PM
driver diagnosis agrobler Multi-Way 3 26th April 2006 12:58 PM
Symptom Diagnosis please? panos29 Multi-Way 12 18th April 2003 04:51 PM
Diagnosis needed! fender4 Solid State 14 3rd July 2002 09:18 AM


New To Site? Need Help?

All times are GMT. The time now is 03:18 AM.


vBulletin Optimisation provided by vB Optimise (Pro) - vBulletin Mods & Addons Copyright © 2014 DragonByte Technologies Ltd.
Copyright 1999-2014 diyAudio

Content Relevant URLs by vBSEO 3.3.2