My alarm keypad has a few nearly-dead buttons and spares don't seem to be available (it's a Karizma plus) so I need to either find another that will work with the system or repair the original. If there was no alternative I'd try to replace the "keys" with momentary switches but I'd prefer to keep the membrane if possible. Has anyone here successfully repaired membrane keypads? If so, how?
Why is the membrane failing? Breakup of the outer surface due to use or just intermittent contact? For the latter you might be able to open up the membrane and clean the contact faces.
See if there is suitably sized third party replacement. Assuming it's a simple X/Y contact arrangement. Might have juggle connections around to get the pinout correct.
The problem is that some keys need very hard pressure or "jiggling" to get a contact. When I've previously tried to fix similar things (TV remotes) by cleaning the PCB it's always been a short term fix, presumably because of a lack of conductive "stuff" remaining on the membrane. I'd prefer to try a repair because of the printing on the membrane and, as it's a common problem, I was hoping that someone here might have found a long term fix.
I've done it with conductive paint, but you'd have to somehow separate the membrane if the contacts are in 'bubbles'.
What type is it. Type one two sheets of flexible pcb with a rubber or hard button on top. Normally can be fixed by silver loaded paint if you can get the layers apart without doing more damage.
2 blister ones where the top of the blister is conductive inside and shorts connections underneath. Very hard to fix successfully since you can't get in to them 3 The remote control type, bumpy pcb underneath, where the contact points are higher and the bottom of the button coated in a conductive material. These tend to dry out and turn to powder and this fills the gaps and either shorts some keys out or stops what is left of the conductive button from making a contact. In this case, disassemble Clean the pcb using an ultrasonic cleaner bath to get the gunge out, and then see if you can get it to work. In the end though the conductive material goes and you end up having to glue ally foil to the buttons, which is both fiddly and can eventually fall off. I feel sure these makers could come up with a better solution than any of these myself, even if its just a bit of springy phosphor bronze below the keys, but I guess these other things are almost off the shelf solutions for simple keypad designs.I'm sure others will have their pet methods, but in the end a new assembly might be better for something so crucial as an alarm where key repeats might lock you out. Brian
I've assumed, from the feel, that it's the sort where a conductive area on the bottom of the button bridges tracks on a PCB. I won't be able to dismantle it for a few weeks but until then I might try changing the codes to avoid the worn-out digits.
Might be of some use...
I repaired rubber PCB buttons on a crossword dictionary (like a calculator only more keys) by gluing pieces of thin conductive plastic on the worn previously conductive surfaces. The plastic was from a black anti-static bag used for electronic components, and the glue was a thin smear of RTV silicone.
It worked for a few years and probably still would but the owner snuffed it.
Cheers
Yes...
I'm assuming silicone-rubbery membrane, black conductive spots press on parallel tracks on circuit board? And you have cleaned the "rubber" and the pcb and it was better but it needs lots of pressure because the conductive bit doesn't conduct well?
I got a very small bag of conductive rubber spots and a tiny tube of special glue, much like silicone sealant. Clean with acetone, shave off a bit of the old rubber with a scalpel for clearance (which was probably unnecessary), stick on the tiny very thin spot, job done. It's lasted very, very well.
(I have 97 rubber spots and a tube of dried hardened glue here, somewhere, probably...)
I think this is the same item and a similar price:
REPLACEMENT Rubbers for Remote Controllers -Pack of:100 Conductive Rubber Pads
Thomas Prufer
Vielen Dank, Thomas. That's exactly what I was looking for but didn't know existed.
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