12 Sep
2020
12 Sep
'20
10:41 a.m.
I got an LK201 recently that was a little damaged in transit. A couple of the keycap
assemblies and their corresponding leaf springs have come off. I can see how the leaf
springs fit on the little posts on the keycap assemblies, and I can see where those snap
into the board, but what I don?t see is how to get that put together and then keep it
together while I turn it over and then get it in place.
Clearly there is some simple trick I am missing. What is it?
Adam
13 Sep
13 Sep
8:04 a.m.
On Sat, Sep 12, 2020 at 6:41 PM Adam Thornton via cctalk
<cctalk at classiccmp.org> wrote:
I got an LK201 recently that was a little damaged in transit. A couple of the keycap
assemblies and their corresponding leaf springs have come off. I can see how the leaf
springs fit on the little posts on the keycap assemblies, and I can see where those snap
into the board, but what I don?t see is how to get that put together and then keep it
together while I turn it over and then get it in place.
Clearly there is some simple trick I am missing. What is it?
When it was made, those posts were much longer. After fitting the leaf
springs and fitting the unit to the membrane/chassis plate, the posts
were melted and formed over to make a large 'head' that held it all
together (this is commonly called heat staking).
My guess is that the formed over part has broken off (you might find
some little white disks of plastic, about 1/8" diameter, rattling
about inside the case). Alas I have never found a way to re-fix them.
There's not enough plastic in the housing to drill it out and fit
screws/nuts. There is no way of gluing something to the ends of the
posts that would be strong enough,
-tony
6:44 p.m.
Tony said
Perhaps using a 3D printed jig, I would set up the key post in a lathe collet and
drill a sub-millimetre hole through the axis. Then glue a sliver of carbon
fibre rod in, lastly mill some channels a few thou deep along the outside of the post
for binding with a strand of de-braided Kevlar thread to hold the end on.
A tiny drop of cyanoacrylate applied with a sharp toothpick keeps the Kevlar
in place. The end cap would be drilled with the same drill.
I've used this CF+Kevlar method for repairing a number of things where there is not
enough surface area for adhesive alone and I am sure the repairs will outlast the items
I've fixed. It takes some patience and a need to set up the job reasonably carefully.
Steve.
On Sat, Sep 12, 2020 at 6:41 PM Adam Thornton via
cctalk
<cctalk at classiccmp.org> wrote:
>
> I got an LK201 recently that was a little damaged in transit. A couple of the keycap
assemblies and their corresponding leaf springs have come off. I can see how the leaf
springs fit on the little posts on the keycap assemblies, and I can see where those snap
into the board, but what I don?t
see is how to get that put together and then keep
it together while I turn it over and then get it in place.>>
Clearly there
is some simple trick I am missing. What is it?
When it was made, those posts were much longer. After fitting the leaf
springs and fitting the unit to the membrane/chassis plate, the posts
were melted and formed over to make a large 'head' that held it all
together (this is commonly called heat staking).
My guess is that the formed over part has broken off (you might find
some little white disks of plastic, about 1/8" diameter, rattling
about inside the case). Alas I have never found a way to re-fix them.
There's not enough plastic in the housing to drill it out and fit
screws/nuts. There is no way of gluing something to the ends of the
posts that would be strong enough,
-tony
10:27 p.m.
At 10:41 AM 12/09/2020 -0700, you wrote:
I got an LK201 recently that was a little damaged in
transit. A couple of the keycap assemblies and their corresponding leaf springs have come
off. I can see how the leaf springs fit on the little posts on the keycap assemblies, and
I can see where those snap into the board, but what I don???t see is how to get that put
together and then keep it together while I turn it over and then get it in place.
Clearly there is some simple trick I am missing. What is it?
Adam
"a couple" ?
Heh. I recently bought an old HP 1640B protocol analyzer, very cheap. Turns out some
genius had
'lubricated' all the front panel button mechanisms. They are the red-bodied HP
'buckling spring'
type, that are heat-staked to the PCB.
The 'lubricant' had aged into something with glue-like properties. Also a bit
corrosive to PCB traces.
I've cut off the melted plastic dots and removed ALL the switches, then disassembled
the switches.
Still to be carefully cleaned.
Then there's the small problem of reattaching 34 switch bodies to the PCB, without
enough plastic
in the studs to re-heat-stake them.
I'm hoping superglue in the PCB holes may work. But the idea of UV-curing Bondic
mentioned above
sounds appealing.
Oh, and 3 of the key switches have broken center shafts too, so I need to find some spare
switches.
Guy
1565
days inactive
1567
days old
3 comments
4 participants
participants (4)
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ard.p850ug1＠gmail.com -
athornton＠gmail.com -
guykd＠optusnet.com.au -
steven＠malikoff.com