Awkward power tranny to heatsink spring clip

[N Cook]

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.

 

[N Cook]

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.

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.

 

[Heinz Schmitz]

http://home.graffiti.net/diverse:graffiti.net/clip.jpg

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.

 

[Ron(UK)]

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 .

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

 

[N Cook]

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

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.

 

[Heinz Schmitz]

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.

Absolutely. Having fiddled with these things often enough it is
hard to imagine how volume output can be achieved otherwise.

Regards,
H.