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Hints, Tips and Solutions (Do NOT post requests for help here) If you have any useful general hints and tips for vintage technology repair and restoration, please share them here. PLEASE DO NOT POST REQUESTS FOR HELP HERE!

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Old 28th Feb 2022, 6:27 pm   #1
Deltatango
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Default Adhesive Foil switch pad removal

Working on an old Sefram 7835 with an adhesive foil switch pad 17 x14 cm and am not likely to get one from the company, thought about creating a "mechanical" version with a pcb and low profile tact switches.

I am undecided though how to unstick it without much damage, the top layer I would reuse with the symbols on it while need to follow the track print it has to create a new layout.

Poor thing has had a very bad life crunched and broken open with a vice so bent and twisted, fixed the lower case so needing to flatten the top (switches on it are duff anyway). Cured other faults and it seems to work fairly well now.

So any good ideas about this unstick issue please

David
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Old 1st Mar 2022, 8:23 am   #2
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Default Re: Adhesive Foil switch pad removal

Heat, I would start with hot water, no chance of overheating unlike a hot air gun.
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Old 1st Mar 2022, 8:26 am   #3
kellys_eye
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Default Re: Adhesive Foil switch pad removal

If the panel is flat enough try an electric iron (with separating cloth).
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Old 9th Mar 2022, 12:01 am   #4
Deltatango
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Default Re: Adhesive Foil switch pad removal

So far so good that is a fight I would like to avoid again!

Thanks for the tips, steam got me a doorway in, but a bottle of sticky stuff remover did that first stage (lots of it) managed to part then its top legend layer + switch sheet from the aluminium case top.

That left me with an aluminium cover with a thick layer of transparent gel like sticky stuff to shift.
Tried to scrape but it fought back, so I needed a release agent, then followed Meths, White Spirit, Nail Paint Remover, Sticky stuff remover, Xylene (modern day cellulose thinners), WD40 car degreaser to name but a few, the last did soften it but as you tried to rub it clear it just got sticky again.

Tried a can of freezer then my hot air desolder tool at 450 degC it just sat there, in the end went with Xylene (open windows and float into ?? with its fumes) wish I had some carbon tet' but that got restricted long ago. What I found was that Xylene did soften it a bit but also made some of it go "crispy" enough to scrape just a little bit with a hard plastic tool.

It was too strong to roll with fingers and still wonder what it was based on certainly not petrol more like some silicone, anyway I will not be doing another under the old manufacturing rule for service engineers (You made it you fix it) that being a clean version!

Just leaves me to part its legend with contact sheet (sticky stuff remover) I think, it reacts also to breathing on so is a lot weaker than the other, so heat may also work but may cause stretching so gentle chemical is the way I think.

That just leaves a Matrix board, just under 40 smd switches and 30 gauge wire to make a new keypad for it plus a bit of working out.

Hope this gives some hints and tips to others but do be aware of adverse reactions to materials (Plastics and Humans etc).

Thanks from David
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