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Thread: Failed Mean Well power supply and questionable diagnostic techniques

  1. #1
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    Unhappy Failed Mean Well power supply and questionable diagnostic techniques

    I just had a "new this year" Mean Well NES-350-5 300W 5v power supply fail. It's in my garage, so it's protected from weather and temperature doesn't drop below 40.

    Here's what I did to try to figure out the issue (and/or make it worse). I don't think this is the recommended way to figure it out, but I'm open to suggestions for next time.

    • Tried unplugging and plugging back in the supply with and without load. The green indicate LED did not come on at any power.
    • Opened power supply to inspect for blown components or expanded caps or just anything odd, but didn't see anything.
    • Pulled internal fuse and checked continuity with multimeter. Failed continuity! A first sign of a failure.
    • Decided to wrap foil around fuse (I don't think this is a recommended diagnostic technique)
    • Prepared for something to happen, then plugged in the power supply
    • SNAP / SPARKS
    • Quickly unplug the power supply
    • Green thermistor RTH1 blew apart

    At this point, I'm not sure if that's a sign that the thermistor was the problem or just a symptom of an issue downstream. I've ordered a replacement power supply to swap in, so I should have things back soon. I'm trying to decide if it is worth trying to replace the failed part or just give up on the power supply.

    MW_NES-350-5_Issue.jpg
    Christmas 2018 Lights: https://youtu.be/pkcxuiiSdhc
    Halloween 2018 Lights: https://youtu.be/1FM4xhan_G4
    2018 Behind the Scenes: https://youtu.be/jGKUd9HzKGw

    Other shows and behind the scenes:
    https://www.youtube.com/channel/UCg1...c85-wgbnkNiLOw

  2. #2
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    Default Re: Failed Mean Well power supply and questionable diagnostic techniques

    Did you have 240/115 input selected properly?

  3. #3
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    Default Re: Failed Mean Well power supply and questionable diagnostic techniques

    Quote Originally Posted by Bwinter View Post
    Did you have 240/115 input selected properly?
    Set to 115. Has been running things well for the last few weeks. Came home tonight and part of the show was down.
    Christmas 2018 Lights: https://youtu.be/pkcxuiiSdhc
    Halloween 2018 Lights: https://youtu.be/1FM4xhan_G4
    2018 Behind the Scenes: https://youtu.be/jGKUd9HzKGw

    Other shows and behind the scenes:
    https://www.youtube.com/channel/UCg1...c85-wgbnkNiLOw

  4. #4
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    Default Re: Failed Mean Well power supply and questionable diagnostic techniques

    When it blew, were any of the outputs connected (ie downstream short)?

  5. #5
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    Default Re: Failed Mean Well power supply and questionable diagnostic techniques

    Quote Originally Posted by Bwinter View Post
    When it blew, were any of the outputs connected (ie downstream short)?
    I had disconnected everything from the power supply downstream. Whatever is/went wrong is just involving the power supply.
    Christmas 2018 Lights: https://youtu.be/pkcxuiiSdhc
    Halloween 2018 Lights: https://youtu.be/1FM4xhan_G4
    2018 Behind the Scenes: https://youtu.be/jGKUd9HzKGw

    Other shows and behind the scenes:
    https://www.youtube.com/channel/UCg1...c85-wgbnkNiLOw

  6. #6
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    Default Re: Failed Mean Well power supply and questionable diagnostic techniques

    Never. EVER. bridge a fuse! They are popping for a reason!!

  7. #7
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    Default Re: Failed Mean Well power supply and questionable diagnostic techniques

    I bridged plenty of fuses, makes troubleshooting downstream a lot easier , see what smokes, replace
    Flash Flash Blink Blink,,Oh What A Relief It Is

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    Default Re: Failed Mean Well power supply and questionable diagnostic techniques

    Quote Originally Posted by DrewDennis View Post
    Never. EVER. bridge a fuse! They are popping for a reason!!
    Quote Originally Posted by mikel3332 View Post
    I bridged plenty of fuses, makes troubleshooting downstream a lot easier , see what smokes, replace
    This was my dilemma. If you don't bridge the fuse, how can you diagnose an issue downstream without power? I made sure to disconnect everything else before trying it to minimize the damage. If I put a new fuse it, it seems likely to blow again quickly.
    Christmas 2018 Lights: https://youtu.be/pkcxuiiSdhc
    Halloween 2018 Lights: https://youtu.be/1FM4xhan_G4
    2018 Behind the Scenes: https://youtu.be/jGKUd9HzKGw

    Other shows and behind the scenes:
    https://www.youtube.com/channel/UCg1...c85-wgbnkNiLOw

  9. #9
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    Default Re: Failed Mean Well power supply and questionable diagnostic techniques

    Quote Originally Posted by DrewDennis View Post
    Never. EVER. bridge a fuse! They are popping for a reason!!
    you can replace the fuse by wiring in an incandescent light bulb, if there still a short, the light gets bright, it's likely there was a voltage spike and cause the thermistor to short to do its job(burn the fuse), sometime it's easy as replacing it to fix the issue.

  10. #10
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    Default Re: Failed Mean Well power supply and questionable diagnostic techniques

    I would do a sanity check first, on the output check for a dead short (ohm meter). Do the same for all voltage rails that thermister exploding like that means a large fault or your on the edge of its capability for a long time.

    What is your expected current draw/ or better yet tested load?
    Is the load under 80% of my power supply wattage?

    With it off you can also do a ohm test between the power rail inside the power supply basically ohm test across the major capacitors. (make sure to short them first to discharge.) If you find a short you want to remove capacitors till the short goes away. Then replace and put back working components

    You can do a diode test but you often have to remove them from circuit to test.
    Your most likely failure is ether a diode or a capacitor to cause that thing to pop.
    Last edited by kingofkya; 12-12-2018 at 12:44 AM.
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