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Triple output power supply blowing main fuse

Discussion in 'Power Electronics' started by partyanimallighting, Jan 27, 2020.

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  1. partyanimallighting

    partyanimallighting

    287
    3
    Oct 22, 2012
    Hi Wizards, I've got two filed units with blown power supplies. I've swapped out the power supplies in the units with new power supplies but I want to attempt to repair the blown power supplies. They are 120VAC ~ 24VDC/36VDC/380VDC and the 24VDC leg drives cooling fans, the 36VDC drives the main circuit boards and the 380VDC powers up a ballast for a 7R 230W lamp. I scrapped out the power supplies and both have blown fuses next to the AC voltage input (bottom right hand corner of picture). I bridged the blown fuse with a single strand of wire and powered up and the makeshift fuse blew out immediately so I'm wondering how I can go about repairing this if I can't power it up and I'm not seeing any sort of burnout on the board but my eyes aren't trained to spot these problems like you guys. I'm thinking that the two yellow X2-224K capacitors are some sort of protection and may be blown out? Anyone willing to offer me some advice on this?
    POWER SUPPLY 001 FW.jpg
    [mod edit: removed double pictures]}
     
    Last edited by a moderator: Jan 27, 2020
  2. Martaine2005

    Martaine2005

    2,538
    681
    May 12, 2015
    I think this is the perfect scenario for a series bulb. Put an AC 100W in series with the mains in. You can put it directly across the fuse. The bulb will light brightly indicating a short but wont blow any other components. You can now troubleshoot the ‘live’ circuit.

    Martin
     
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  3. Martaine2005

    Martaine2005

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    681
    May 12, 2015
    Incandescent bulb!!
     
  4. Martaine2005

    Martaine2005

    2,538
    681
    May 12, 2015
    Incandescent bulb!!
    You can simply remove the X2 caps for testing. They could have shorted the input.

    Martin
     
  5. Harald Kapp

    Harald Kapp Moderator Moderator

    9,544
    1,970
    Nov 17, 2011
    There seems to be no visible sign of damage.
    I think there is a good chance the primary side power MOSFET has a short. That would be, as far as I can judge, the component labeled 8GL28. I can't find a reference what "8GL28" could be. Are there any other imprints on the case of this component?
    Does the short circuit vanish if you remove this component?
     
  6. Harald Kapp

    Harald Kapp Moderator Moderator

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    Nov 17, 2011
    That would be the 2 yellow boxes next to the AC input.
     
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  7. partyanimallighting

    partyanimallighting

    287
    3
    Oct 22, 2012
    Really? I kind of remember seeing old electricians testing electrical shorts with a bulb and socket with two wires. Here's the funny thing.....I'll have to go buy a 100W incandescent!! Everything I have is LED!! I might have really old stock of effects lighting lamps like 300W 120VAC 64514's lying around somewhere. Do you think they will work?
     
  8. partyanimallighting

    partyanimallighting

    287
    3
    Oct 22, 2012
    I'm not an experienced technician and I know this power supply puts out 380VDC so I'm gonna be extra careful running any tests. A large amount of these lighting units were powered up at the same time so I'm figuring the current draw from all the lamps striking at the same time screwed up the power supplies so I'm assuming the two yellow X2-224K capacitors are part of the problem because I'm thinking they're the "safety" caps for the input voltage leg. As for the 8GL28 mosfet, there's no schematic for the unit and no markings at all on the power supply so it's anyone's guess what that component is. The cap is X2-224K MPX/MKP 40/110/56/8 275VAC 305VAC 310VAC.
     
  9. partyanimallighting

    partyanimallighting

    287
    3
    Oct 22, 2012
    Martaine2005, can you explain to me how putting the 100W incandescent bulb in series across the fuse terminals will prevent the blowout? Does the bulb create enough current draw to decrease or cancel out the short? Please remember I'm not a trained technician so I would like to understand the scenario better.
     
  10. Martaine2005

    Martaine2005

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    681
    May 12, 2015
    The series bulb limits the current. Also acting as a resistor, there is now no short detected. I use different wattages for different appliances. A 300W will work too.
    The X caps are across the input. Removing them has no consequence other than external interference like clicking through speakers or radio interference. A suppressor of sorts. (If I understand it correctly) of course!.
    But you can obviously remove the mosfets and see if the short goes away.
    The series bulb saves blowing fuses too.

    Martin
     
  11. Harald Kapp

    Harald Kapp Moderator Moderator

    9,544
    1,970
    Nov 17, 2011
    Can you show a close up photo of this transistor, please? Maybe it is not 8GL28 after all?
     
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