Our company's Service Department provides monthly field repair reports to our R&D department who looks for patterns and high fallout of components. Over the last 6 to 12 months, we have noticed a high fallout of Power Supplies in the United States. However, we have not been able to find the reason for the fallout. The power supplies have all shown arc damage to the AC front end, signs of arcing and traces burned or vaporized, blown fuses, and shorted FETs and/or Rectifiers. These failures have occurred on several different locations, on different power supply models, different manufactures and on different instruments. Some instruments have been in service for years; some for only a few weeks before they fail. Some instruments even have surge suppression modules installed and though the power supplies fail the surge modules tested out fine. The failures did not occur during any known lightning storm or any other known transient. Very strange.
Of those of you who read these emails, have you experienced an unusual increase in such field failures in the last year? Anyone have an idea of what might be causing this increase? We test our products and power supplies to the IEC 61000-4-4 and 4-5 fast transient and surge immunity tests. We actually test beyond what is required for CE in Europe (often to the limit of our test equipment which is 5kV) and we audit every family of products about once a year. We have performed additional testing of production power supplies of known models that have failed in the field yet no unusual problems have been found. We also perform radiated and conducted RF immunity tests, ESD, voltage dips and dropouts, frequency variation testing, and harmonic and inter-harmonic immunity tests with no discernable problems found. We have AC Line Analyzers running for months at several customer locations and have not detected any unusual transients or reason for the high fallout of power supplies. Two weeks ago we had a power supply blow in one of our own labs on an instrument that had been running for several years. Two R&D engineers were sent over to investigate. They changed out the power supply and verified the instrument was running properly. As they turned to walk out of the room, POW!!, the power supply in the instrument next to the one they just fixed blew up. A power line analyzer has been running ever since but not unusual transients have been detected, yet. Are we missing something? Is there additional transient tests that we are not performing that we should be? Is there something we should be looking for and are not? Has this last year been unusually bad for power grid problems, sun spots, alien transmissions, ?? We are stumped. Thanks for any advice and comments. The Other Brian ________________________________ LECO Corporation Notice: This communication may contain confidential information intended for the named recipient(s) only. If you received this by mistake, please destroy it and notify us of the error. Thank you. - ---------------------------------------------------------------- This message is from the IEEE Product Safety Engineering Society emc-pstc discussion list. To post a message to the list, send your e-mail to <emc-p...@ieee.org> All emc-pstc postings are archived and searchable on the web at: http://www.ieee-pses.org/emc-pstc.html Attachments are not permitted but the IEEE PSES Online Communities site at http://product-compliance.oc.ieee.org/ can be used for graphics (in well-used formats), large files, etc. Website: http://www.ieee-pses.org/ Instructions: http://www.ieee-pses.org/list.html (including how to unsubscribe) List rules: http://www.ieee-pses.org/listrules.html For help, send mail to the list administrators: Scott Douglas <sdoug...@ieee.org> Mike Cantwell <mcantw...@ieee.org> For policy questions, send mail to: Jim Bacher: <j.bac...@ieee.org> David Heald: <dhe...@gmail.com>
