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Voltage fluctuation on 12VDC/24VDC dual output P/S

Discussion in 'Power Electronics' started by partyanimallighting, Dec 7, 2019.

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  1. partyanimallighting

    partyanimallighting

    309
    4
    Oct 22, 2012
    So......if it is a linear voltage regulator it's possible that it could be the cause of the problem as it's common to all four power supplies? I could check the voltage readouts on the legs, couldn't I? Creating a schematic from the PCB (wow!!) seems a bit much for me. :confused::confused: With my limited background in electronics, should I give it a try or just abandon this particular repair (x4)? I do have two other triple output power supplies that I'm trying to repair that I was thinking about posting as I'm kinda stuck in limbo on these four power supplies. :rolleyes::rolleyes:
     
  2. Harald Kapp

    Harald Kapp Moderator Moderator

    10,025
    2,138
    Nov 17, 2011
    Possible yes. How likely is hard to tell. Anyway, without knowing what chip this is, repair is going to be very difficult if not impossible.
    Do you have a working unit? You could swap this component from the working unit to the defect one to see whether this one ic is the reason for malfunction. Once it has been established that this ic is the culprit, maybe examination of the other ics reveals which part number is required for replacement.

    It is not as difficult as you may think. Simply follow the traces between components and draw the components and their connections. When you start from the suspect ic you will soon be able to recognize the circuit, possibly after rearanging the components in the schematic to match the "typical" voltage regulator schematic. See this example.

    Looks like this power supply is a bad design as you seem to have multiple failed units :(
     
  3. partyanimallighting

    partyanimallighting

    309
    4
    Oct 22, 2012
    And I don't have a functional working unit to test with anyway. I think I'll put them on the back burner and move onto the two triple output power supplies waiting in the wings. I'll still try the schematic in the interim based on your example.
     
  4. Martaine2005

    Martaine2005

    2,751
    742
    May 12, 2015
    When reverse engineering for a schematic, I find it easier to print off the reversed back side of the pcb. Then draw the components across the solder joints. I always use a flash light for illuminating through the board to verify my connections. Adding component values also helps too.
    When I am lucky enough to have a working unit to compare with, I add voltages as well.
    I find the first half hour the hardest as I’m constantly flipping the PCB and using the flash light.
    I would be surprised if it took you an hour to draw your board out. Then you can start with the schematic as things come clearer to you.
    Always work from supply in on the left to output on the right.
    Hope this helps.

    Martin
     
  5. partyanimallighting

    partyanimallighting

    309
    4
    Oct 22, 2012
    So this is what I've done so far. I had to pull a few components to get their value but that all goes to the learning experience. Please take into consideration that this is my first attempt at drawing a schematic so that brings me to my first question. Is there anywhere that can I download a zip file or folder of jpg's of the various component symbols so I can import them or drag and drop into my "schematic" next to the values?

    SCHEMATIC FW.jpg
     
  6. Martaine2005

    Martaine2005

    2,751
    742
    May 12, 2015
    There are a few free programs that do this. Many on here use LTspice. It has libraries of components. It also comes with a learning curve.
    There are Apps too. But I’ve never used one.
    Hopefully somebody else will chime in to help you.

    Martin
     
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