R5 Burnt Out in P48 Circuit

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  • #15413

    Hello Ted,

    I hope you are well.

    In one of the 828s that I look after, R5 has burnt out and gone o/c, momentarily (so I understand) taking the whole supply down with it. The device IC1 itself is not (at least now) s/c between pins 14 and 11/3, and on-board measurements (still with device removed) show that TR2 and 3 are still intact (i.e. not s/c C-E).

    Is this something you’ve seen before?

    With the device being obsolete, I’m proposing to dispense with P48 altogether, but have yet to get approval on that. I was just wondering if this is a known issue with this DC-DC convertor design.



    Ted Fletcher

    No, I have never seen this problem before.

    That power supply is normally, in fact always, reliable, so I can’t comment.

    Of course, it’s an old design, but it really has stood the test of time, so I suggest replace the parts and carry on using it! :)


    Thanks Ted,

    Let’s hope this doesn’t represent the back end of the bathtub curve! (Managed to procure a replacement device, anyway. Despite its obsolescence it is fortunately not rare, it seems.)



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