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Awkward power tranny to heatsink spring clip

Discussion in 'Electronic Repair' started by N Cook, Jun 10, 2007.

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  1. N Cook

    N Cook Guest

    Anyone know the correct way to remove and replace or even initially place
    (without possibly straining the legs of the tranny by lateral forces) such
    spring clips as in this 2 angle view ,combined pic, I took
    http://home.graffiti.net/diverse:graffiti.net/clip.jpg
    I slid a thin piece of PTFE sheet between body of tranny and the clip ,
    pulled outwards with thin nosed pliers, and then drove the clip along the
    slot in the aluminium heatsink, with a punch and hammer to undo, but how to
    reassemble. I've slid the clip along the slot (slot profile shows just under
    the red "S" on the other heat sink) but not replaced over the tranny for
    the pic. It requires pulling and sliding at the same time
    The one pictured has space in front to manipulate with perhaps a lever with
    2 pins do the double operation of pull in one direction and push
    transversely at the same time but its complement is hidden behind some large
    caps, so not possible with that one.
    Its not possible to just push the top of the clip into the slot as is often
    the case with other such spring clips.
     
  2. N Cook

    N Cook Guest

    Thr best I can think of so far for clipping or unclipping.
    Grease in the slot and a small wedge to the thickness of the transistor laid
    to the side of the transistor and a thin covering of PTFA sheet over the
    wedge and transistor and lever or push or hammer+punch the spring clip
    across.
     
  3. Looks like when the replacement transistor isn't yet soldered
    to the board you can lower it enough onto the board to lever
    open the spring and shift the transistor upwards under it.
    Messy procedure, though, with heat conducting paste applied.

    I would seriously consider to mark the hole of the transistor onto the
    heat sink, take that off the board, drill a decent hole and to secure
    the transistor onto the heat sink with a screw and washer like it was
    always done in valuable devices :).

    Regards,
    H.
     
  4. Ron(UK)

    Ron(UK) Guest

    I bet that during manufacture, the devices are fitted to the heatsink
    first then the whole sink assembly fitted to the circuit board and
    soldered up by hand. I`ve seen it before where one bad transistor was
    impossible to remove without unsoldering them all and lifting them away
    with the metalwork.

    Ron(UK)

    www.lunevalleyaudio.com
     
  5. N Cook

    N Cook Guest

    Email reply from the amp maker's engineer
    "As to the spring clips, there is no real way of removing and refitting
    those, except by sliding them on to the heatsink slots. That can only be
    done when loose (no devices
    in place ).
    Hence, they have to be mounted on to the heatsinks before sliding
    them over the devices."

    My bit of (clothes line peg) wedge and ptfe sheet method did work but if the
    applied force along the slot, is not axial to it then the high-C steel clips
    easily dig into the aluminium and jam fast. I found a large pair of
    engineers cramps would gradually inch it across, taking up the slack every
    few mm , and starting again. Just another thought, with a pair of large
    sewing thimbles on opposing finger/thumb you may be able to use enough
    finger pressure to slide the clip up the wedge.
    But otherwise matter of desoldering the power devices and removing the
    heatsink with trannies and then the trannies can be easily slid out from
    under the springs.
     
  6. Absolutely. Having fiddled with these things often enough it is
    hard to imagine how volume output can be achieved otherwise.

    Regards,
    H.
     
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