Surface mounted Thru hole Caps

Discussion in 'Electronics & Electrics' started by @rt, May 14, 2016.

  1. @rt

    @rt Member

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    Hi Guys,
    This is board is a Chinon CD controller from the 90’s.
    I’m wondering what reason in commercial production in Japan would have to do this?
    This is a more costly production if SMD/Thru hole capacitors are all the same.
    Personally I have distrust of SMD caps, and would do the same, but didn’t expect to see it commercially.
    Are these pads much bigger than the SMD footprints?
    I can see the are a little bigger, but doesn’t look like much.

    [​IMG]
     
  2. mtma

    mtma Member

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    Those don't seem to be SMD PCB footprints to me, are you sure they're not through hole?

    ED- as for the why would they produce something like this question, think of it this way:

    1. You have an existing design of the PCB's, a few pallets of several thousand of the same PCB in the warehouse paid for already.

    2. You either can't find the parts that were meant to go onto the PCB anymore, or purchasing has already purchased hundreds of thousands of these parts ready to assemble.

    3. Management makes a decision: scrap the boards or the parts, redesign and not have a product on the market for months while the process happens or add man hours to the production for now to buy more time to see whether the former is worth doing at all.
     
    Last edited: May 14, 2016
  3. OP
    OP
    @rt

    @rt Member

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    SMD footprints for electrolytics are rectangular IIRC, so they are larger pads,
    but this is at least a dual layer board. Look at all the vids around the ground plane.
    Surely they can’t line all those caps up to the other side?
     
  4. OP
    OP
    @rt

    @rt Member

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    No, I can see the legs splayed out sideways on a couple of them
    Far left, and top right.
     
  5. mtma

    mtma Member

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    I'm not following you with the one image you've posted so far. I haven't spotted anything to suggest that the caps aren't just on through hole footprints of the wrong pitch.
     
  6. OP
    OP
    @rt

    @rt Member

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    I don’t actually have the board to look at.
    I agree the footprints aren’t SMD footprints, and the silkscreen is also different
    than I’m used to for a board that intended to have SMD caps mounted on it,
    but it also looks to me like the thru hole caps are surface mounted, and their leads aren’t going through the board at all.

    I’ll try to find a pic of the other side. It is all dense smt.

    EDIT:
    Forget whole thread lol. They are all thru hole mounted.
     
    Last edited: May 14, 2016
  7. dohzer

    dohzer Member

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    Just smaller radius caps mounted with bent pins, right?
    Who knows... maybe they planned for a different (voltage, capacitance, family) cap and changed them, or just couldn't source them. And changing the PCB may have been too expensive compared to a pin bending machine/child.
     
  8. mtma

    mtma Member

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    In this instance I think it would have been a time to market thing.

    Particularly notable is that all the polarised cap patterns - regardless of the size of the actual part - have the same size capacitor pattern on the PCB.

    There are of course a variety of reasons why this might have occurred, but the fact that it went into production as we see it basically points back to time to market as the most probable core reason.
     
  9. OP
    OP
    @rt

    @rt Member

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    I might still be misunderstood.
    I thought the caps had their leads cut short and
    surface mounted.. ie. Leads not going through holes to the bottom layer,
    but not the case. I found a pic of the other side of the board.
     
  10. merlin13

    merlin13 Member

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    Couple of points to note for SMT:

    - SMT capacitor 'n resistor pads are never round, unless whoever was doing the component layout etc was on serious drugs. Have seen older boards laid out using rectangular pads with the short sides rounded, often for diodes though;

    - throughhole parts can't be placed or soldered on SMT pads by bending and trimming the leads short, because they'd fall over as soon as the machine let go after location placement on the board. Hand placed and soldered yes, but not in serious production quantities...
     
  11. OP
    OP
    @rt

    @rt Member

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    Yes, that’s what I meant, it would have increased production cost in any case.
    Even the trough mount had to be done by hand anyway.

    Interestingly the big Sony chip on the board is intelligent enough to output
    status for focus lock and C1 & C2 error count among other things, and also can be told to skip tracks, etc.
    I think from that drive controller, it’s only down to a DAC, PSU, display and amp to complete the CD player.
     
    Last edited: May 16, 2016

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