Turned SMPS (Condor GPC55C) off-on in rapid sequence: dead

Discussion in 'General Electronics Chat' started by felixed, Dec 17, 2008.

  1. felixed

    Thread Starter New Member

    Dec 17, 2008
    Have a slide imager (PCR II Plus) powered by a Condor GPC55C quad output smps. Worked well till I inadvertendly turned it off - on in a rapid sequence. The manual strongly warns against doing so. The switcher is dead. Put a healthy smps (identical model) from another machine to make the imager work again. To track I measured the output voltage of both, the failed and the healthy one, off machine. Strangely I get no voltage on both. Maybe the voltage is not present under no load? The good smps still works. How can I track the faulty part? Only part looking unhealthy is the feed back dip6 optocoupler: its leads and around the part covered with some greyisch powder. Could it be the culprit? The electrolytics are not bulged. The transistors look normal. Unsoldering the mosfets would be tricky. Couldn't find any schematics for this obsolete smps. Even the smps itself seems a rarity.
    Any suggsetion would be appreciated.
  2. S_lannan

    Active Member

    Jun 20, 2007
    It's not easy to track the faults in SMPS unless you are quite experienced.

    Perhaps a surge of current damaged something on the primary side of the power supply due to the rapid on/of cycling.

    by the way, switch mode power supplies aren't the most forgiving things and they can store lethal charges in reservoir capacitors even when unplugged.
  3. eblc1388

    AAC Fanatic!

    Nov 28, 2008
    I hate to point out the obvious but I guess you have already checked the fuse next to the AC input connector is not blown?

    I don't think the optocoupler is the culprit.

    There are a lot of companies on the net advertise for the repair of this particular model of SMPS but I'm sure it will cost at least 80% that of a new one. Digitkey still have them I think as many search results come up with its websites all over the world.
  4. John Luciani

    AAC Fanatic!

    Apr 3, 2007
    This is the most likely problem. Most of these power supplies have
    a PTC in series with the input caps. When the power supply is cold the PTC has
    a high resistance and limits the current to the input caps. As the PTC heats the
    resistance drops.

    If you cycle the power when the PTC is hot you get a large surge current into
    the input caps. You could have blown a fuse or breaker in the supply or the input
    caps. The caps have a series resistance (ESR) so a large current will cause
    internal heating and they usually explode.

    (* jcl *)
    Last edited: Dec 19, 2008