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Brittle Keyboard Membrane

Posted: Thu May 21, 2020 8:14 am
by bwinkel67
I got bit with that today. The membrane had only been used for about 6 month but it was an old replacement one I bought in the 90's that I kept in a cool dark place. To help it from cracking I backed each side of the two strips with clear thin packing tape which gave it a bit more rigidity. I had initially plugged in the connectors with the tape backing all the way down. When I had to fiddle with the machine during the time I had a failing QL (needed to re-seat my chips) one or two of the metal contacts wore through on the membrane because I had to keep taking it apart so I cut the bad piece away and removed the tape backing when I reinserted. Well, that section today decided to crack so I went and cut off another 1/4 of an inch to the tape backing and stuck it in with the backing so 6 of one and half a dozen of the other I suppose. Will see if the tape backing will do a better job.

Would the extra thickness that a thin strip of tape adds (less than half the thickness of the membrane) cause issues in the future for the metal connector tabs getting looser? It's just metal contacts designed to give and bend back, right? Are they resilient enough to deal with a little extra width? I wouldn't want to screw that up in order to prolong a membrane. Anyone have any ideas? Are the new membranes the same thickness or thicker? I have one and it feels different.

Re: Brittle Keyboard Membrane

Posted: Thu May 21, 2020 10:09 pm
by bwinkel67
So indeed, the new membranes are slightly thicker than the old ones from the 90's. I had bought two replacement ones back then (coming from the UK, shipping on two was just more practical), of which one is presently in my QL having replaced, I believe, the original one that finally broke back in November (maybe it was a replacement, can't remember). I ordered a new one from SellMyRetro and now have both a 90's and a 2019 as replacements. The latter is much more sturdy and slightly thicker. In fact the tape backing I put on the old one to give it more rigidity seems to be almost the same thickness now as the new one.

I used the scratch test, placing the old connecting end to the new connecting end on a flat surface, and fingernail in one direction doesn't catch and in the other it does. Once the tape is added no catching in either direction. Adding the tape backing does give the older membrane a sturdier, less brittle, feel so if anyone has an old membrane that you are about to put in, or are cutting off a 1/4 of an inch of an existing one to re-insert, let me recommend some clear packing tape (a little thicker than scotch/masking tape but shiny and less than half a thick as the membrane) to strengthen the material so it ends up staying curved and doesn't collapse and crimp which causes the fine metal contact to break and lose key presses.

You can buy new ones that are better, but a little bit of tape and you don't have to waste one created back in the day (well, I think even then they might have been after market ones). I like the idea of not wasting anything :-/