Declan Moriarty: > I have the repair job on 3 dc/dc converters, worth a lot, but very > awkward. They have a switched transformer feeding 3 further switched > stages (+24VDC in , +/- 15V out, &aux supply). Some problem fed 24V back > up a +15V line. I have removed all visible shorts and faults, and still > the input switched stage will not run, so the second 2 receive no power. > > I have 2 questions: > 1. Why - what's it thinking? How does it know the outside supply > is/was buggered?
When 24V appeared on the 15V output, several things probably happened. The output capacitors probably aren't rated for that voltage so they'd go pop. Current trying to flow though the inductors would then probably increase which may or may not burn them out. There has to be some kind of feedback system to whatever controls the switching rate which may or may not have seen overvoltage. If the control chip had seen overvoltage it may not be powering up now which is why no current would ever see the secondaries. I'd find whatever circuit is controlling it and see if it's providing pulses to the switching transistors. If not it's not starting up and you can then ask why that is. Find the docs for the controller, see if it's input pins have the right conditions and take it from there. > 2. Any ideas on this thing in the middle of this pcb. It looks > like a pcb 'sandwich transformer', and has loads of connections > off the pins underneath. The black part in the middle is ferrite > > http://homepage.ntlworld.ie/e-tronic.genius/smpsucard.jpg I'd say it looks like a pcb 'sandwich transformer' as you suggest as you can see the coiling pcb tracks. The ferrite is acting like a transformer core. I'd see if all the tracks are intact with a meter... -- RP -- Author: Richard Purdie INET: [EMAIL PROTECTED] Fat City Hosting, San Diego, California -- http://www.fatcity.com --------------------------------------------------------------------- To REMOVE yourself from this mailing list, send an E-Mail message to: [EMAIL PROTECTED] (note EXACT spelling of 'ListGuru') and in the message BODY, include a line containing: UNSUB CHIPDIR-L (or the name of mailing list you want to be removed from). You may also send the HELP command for other information (like subscribing).
