First, I'd like to apologize with the list for the multiple message, I sent it several time because I didn't realize there's some latency in posting. Bob, I was quite sure you had something to say about it, i remember you had on your web a PS for the car mp3 player ;-) I forgot to say I put a linear stabylized 5V power supply on the primary output (thus the feedback line) in order to check against the aluminium caps with no luck. Also I saw that the secondary 12V output line is used by a transistor to help rising feedback line to stop the UC3844 by means of a photo coupler. Also that line has been isolated and fed by a 12V stabylized supply. The led inside the opto switches on at about 5.08 V (again externally driven by the test power supply), so in my opinion the feedback line is ok. I am still afraid the problem is on the primary winding side, expecially about timings I haven't heard of in your reply (what's your opinion about the freq? ). Also notice I have two PS: the one broken and another that would be broken soon. :-( The latter works fine ONLY IF THERE'S LOAD on the 5V line, else it shows the same behaviour as the former. Thanks a lot!!! Alessandro ----- Original Message ----- From: "Bob Blick" To: "Microcontroller discussion list - Public." Sent: Thursday, December 01, 2005 5:25 PM Subject: Re: [ee]: UC3844 switching PS repair >> I 'm trying to repair myself a switching Power Supply made by ZyXEL. The >> PS >> suffers from 5V line oscillating (actually the PS starts, shuts down, >> starts...). I checked against the output filters and CAPS and they seem >> ok, > > It still sounds like a bad cap to me. Or the resistor that supplies the > startup current has drifted way up. > > Cheerful regards, > > Bob > > > -- > http://www.piclist.com PIC/SX FAQ & list archive > View/change your membership options at > http://mailman.mit.edu/mailman/listinfo/piclist > > -- http://www.piclist.com PIC/SX FAQ & list archive View/change your membership options at http://mailman.mit.edu/mailman/listinfo/piclist