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Thread: LNK420 got cracks in the body with power supply 75 W

  1. #1

    Buttrock LNK420 got cracks in the body with power supply 75 W

    When we use LNK420 ( this one: http://www.kynix.com/Parts/80833/LNK420LG.html and the datasheet: http://www.alldatasheet.com/view.jsp...hword=LNK420LG) with power supply 75 W we have got cracks in the body. The photos are attached. Does it happen often with LNK420? What is the solution?










    i will clarify the situation.
    This is not regular. At the moment is sporadic failure. It was noticed to me that this failure occurs duren transient processes:
    - cyclic switch on/off power supply
    - powerfull surge transients (this it indicated by a destroyed varistor, Y2 capasitor and fuse)
    So, i`m inclined to think that the engineer made a lot of mistakes when developing a power supply:
    - PCB. Design is bad. Does not even meet your recomendation. Reality, is not possible to obtain power above 45 watts, system is not stable. The situation is corrected by adding С18?
    - BOM. No logic. 100V shottky diode (VS-12CWQ10FN), under doubt transformer configuration (ETD29 0,7mm gap N87 Pri: 81T Sec: 20T Bias: 13T), clamp network (1.5KE250), wide range of regulation current (30V 45-75W), C18 in parallel FB pin (Kirchhoff`s circuiit laws ?)
    - As a result we have: low PF (about 0.9), unstable current regulation (more 5%), switch off PS if input voltage under 175 VAC (OVP triger), flickering 30-50%
    Files of project attached. This design copy of RDR-290.







    Last edited by Joshua_S; 04-16-2018 at 04:41 AM.

  2. #2
    Flashaholic
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    Default Re: LNK420 got cracks in the body with power supply 75 W

    I am really not sure what you expect here on a hobbyist board. Why are you not contacting Power Integrations the MFR of the chip?

    Is this your power supply or someone else's because it is NOT the RDR-290 reference design, which I have to question whether you read the specs of, because some of the stated performance is just how that board should perform.

    Could I fix it .... no doubt, but it is not going to be free.

  3. #3

    Default Re: LNK420 got cracks in the body with power supply 75 W

    I apologize. These are not just mine, but the tests and results discussed from us were me who finally put them together and posted here, just wanna ask you guys about this lnk420 failure what you think and what should we do....Do i picked the wrong forum? you said the copy attached was not from RDR-290 so i checked out the info again and sorry for the stupid mistake, maybe this one, correct me if i am wrong please, i still a newbie about these electronic things:

    Not sure if i could afford the cost
    anyway thanks for your reply and have a nice day.

  4. #4
    Flashaholic
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    Default Re: LNK420 got cracks in the body with power supply 75 W

    Still have not said if it is your companies design, something you buy assembled, etc.

    I would suggest you contract someone who knows what they are doing who has the proper equipment and knowledge to analyze the issue.

  5. #5
    Flashaholic* DIWdiver's Avatar
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    Default Re: LNK420 got cracks in the body with power supply 75 W

    Quote Originally Posted by ssanasisredna View Post
    Still have not said if it is your companies design, something you buy assembled, etc.

    I would suggest you contract someone who knows what they are doing who has the proper equipment and knowledge to analyze the issue.
    I agree. This is not the place to try to resolve design issues in a commercial product. If you want advice like "don't run it at 75W, only run it at 45W" or "that's junk, don't buy it", we maybe can help, maybe not, and you wouldn't expect to pay for that advice. But if you are looking for advice on how to fix a commercial product, you should expect to pay for that.

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