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Why wouldn't a rubber membrane button work?
MUFF WIGGLER Forum Index -> Music Tech DIY  
Author Why wouldn't a rubber membrane button work?
tIB
Got an eBay purchase yesterday where everything worked except one of the (9 or so) rubber membrane buttons - they're the type found on lots of cheaply made synths that have some kind of conductive material that closes a switch on the PCB.

I did some rudimentary testing and found I can (sometimes) trigger the button directly on the PCB with foil, however when mounted to the button it didn't work. Pencil on the button contact didn't either, or contact cleaner on the PCB.

If there is anything else simple I could try let me know - seems very strange to have such a simple part of the machine fail... I was hoping what I'd tried would sort it as I really don't want an elongated eBay back and forth.
cnicht
Be very careful cleaning with contact cleaner as it can leave a residue.

The advice I received from a synth service centre was to wash the rubber part in 500ml of warm water with one drop of washing up liquid and let it dry naturally (sounds odd but it did work for me) Apparently the sulphur dioxide in the air combines with rubber to make it non-conducive and this process removes the contaminants from the surface.

The conductive pads should be cleaned with a clean non-abrasive pencil eraser. Cut off any grot getting onto the eraser. Don’t use any solvents, sprays etc.

The use of any chemicals should be avoided (apart from the detergent used to wet the conducive rubber)

Hope this helps (don’t flame me please if there’s a manufacturing fault with what you’ve got!)
tIB
No flames here, appreciate the help! I did the rubber/eraser trick before using contact cleaner. The washing up liquid thing is a good one that I've not tried - however I'd expect to have more success triggering the switch with aluminium foil (unless I'm missing something there)... Im guessing it's an issue on the PCB?

I'll see what the company and guy I brought from say - I'm happy to mess with it some more if they are as I'd really like it to work...
JohnLRice
Is it possible to temporarily swap one of the working buttons to the non-working PCB pad position and vice versa? That might help clarify if it's the button that isn't conducting or if the problem is on the PCB?
tIB
It probably will be but am waiting for the green light to hack around further from the seller - the buttons have a couple of glued standoffs so can't currently be interchanged. It won't take much to free them up though.

With the PCB I could trigger pause/play easily enough with the foil, and there is a visible mark on the PCB surface on one side of the contacts - is there a way to repair the PCB surface easily if that's a break or is a new PCB needed? Again I can't really do that until I have the ok.
cnicht
If the conductive rubber pads are completely shot I did see a company doing replacements. There are also these on eBay (although you may not want to fish again in that pond!)

https://m.ebay.co.uk/itm/1-5-10mm-Repair-Music-keyboard-TV-Keypad-Remo te-Control-Conductive-rubber-button/302462350093?_trkparms=aid%3D22200 7%26algo%3DSIM.MBE%26ao%3D1%26asc%3D20180213162448%26meid%3Dc21bb8ac1a f94560a812cd84d930b19f%26pid%3D100930%26rk%3D2%26rkt%3D8%26sd%3D181662 188354%26itm%3D302462350093&_trksid=p2056116.c100930.m5375
tIB
Good shout, cheers! I was hoping the alu foil hack would sort it but it only worked the once when mounted toothed button. I could get it to work intermittently when just jabbing away at it with foil direct.

I tend to think it's a pub issue but will check in more depth if the seller responds.
robin87
I had the same problem on some synth keyboards. A lot of keybeds have little rubber buttons under the keys. Sometimes the rubber/eraser thing brought the keys back to life, on other occasions the conductive coating on the rubber membrane was too worn out.

My solution was to get a bottle of pure graphite powder, put some on a piece of paper, dap a q-tip into the powder and gently wipe the rubber contacts. You'll only want to apply a tiny amount, so be gentle! The powder is really fine and since the rubber itself is kind of sticky, it will coat the contacts easily.

Worked out really well for me, my Poly 61 got the treatment a couple of years ago (90% of the keys were dead when i got it) and I've never had any problems since.
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