Conductive pad buttons - cleaning/rejuvinating?

[Scodiddly]

Got an old Korg Mono/Poly on my bench from one of the kids (for me the "kids" are garage band types in their 20s who love weird vintage stuff), basically keyboard problems. It's got those conductive pad dealies under the keys, and while cleaning helped a lot it still isn't 100%. Now ideally I'd just buy replacements, but do they even carry that stuff anymore?

Failing reasonable access to replacement parts, any hints on better cleaning or rejuvinating?

 

[Emperor-TK]

Can you elaborate a little more about "conductive pads"? Are they membrane touch switches? At my old company, we had customers that printed MTS with our silver ink, so I know a little about them. Typically, a carbon ink layer is printed over the base metal (printed silver or etched copper). This is to reduce friction by eliminating a metal to metal switch. If the carbon layer has worn away, the likelyhood of the metal traces breaking is much greater. If you can get to the contacts, you might be able to restore them with a silver ink pen and some graphite paste.

-Chris

 

[Scodiddly]

This is the same sort of switch you find in Nintendo controllers. On the circuit board there's a little pattern of interleaved traces, and then the other half of the switch is a rubber pad with a little black (carbon or graphite) conductive button in the middle. The rubber acts as a spring, keeping the black button off of the traces.

 

[Mark Burnley]

I've had some luck reactivating the carbon pads with graphite powder. I got one of those artists graphite sticks, the really soft ones, and ground off some of it with a sharp blade so that I had a small heap of raphite dust. I then got a very fine watercolour paintbrush, and lightly dusted the pads with the dust. Be careful to dust off any excess, and then replace the pad onto the contact board.

I've done this on a lot of audio gear, but also TV and video remote controls!

Mark

 

[NewYorkDave]

Cool tip! Do you suppose that graphite powder sold for lubricating locks would work as well? It so happens that the "mute" button on my TV remote is worn out and I've been wondering if I should attempt to fix or just buy a replacement remote.

 

[Mark Burnley]

As long as it isn't combined with any wax or other oily base, then I'm sure it'd be fine. I've even used a 6B pencil- just ground a bit off the tip! If you look at the circuitry around these keypads, they're never looking for a full pullup to +Ve or pulldown to 0V, they're usually pretty hi-Z CMOS inputs, so even a relatively high-resistance (i.e. a small layer of graphite powder) will bring the contact back to life.

It really works though :thumb:

Mark

 

[Scodiddly]

Very cool tip! It would be worth cracking that keyboard back open just to try it out.

Any reason you couldn't just rub the pencil tip right on the pad?

 

[Mark Burnley]

Well I tried that first, but it didn't take very well- once you've got graphite dust on the paintbrush tip, you can really apply a good layer. I've used a similar method to "fix" a pot temporarily whilst waiting for a replacement in the post :grin:

Mark

 

[Emperor-TK]

[quote author="Scodiddly"]This is the same sort of switch you find in Nintendo controllers. On the circuit board there's a little pattern of interleaved traces, and then the other half of the switch is a rubber pad with a little black (carbon or graphite) conductive button in the middle. The rubber acts as a spring, keeping the black button off of the traces.[/quote]

Yep. Basic membrane touch switch. I am typing on one right now :grin:

The carbon layer might have worn off the black button, but your problem might also be the interleaved digits on the PC board too. That surface was most likely coated with a conductive layer too, either carbon ink or a conductive polymer. Try giving that surface a good cleaning and then do the condutive treatment to that too. I still say that the silver/epoxy pen will be your best bet. That will be both very conductive and medium-low friction too.


Check out the FAQ's:
http://store.caig.com/s.nl/sc.2/category.174/.f

 

[Scodiddly]

I went to the local artsy store and got me a 6B graphite stick and a little brush... worked great! All the keys are working fine, and I'll have a very happy customer.

Many thanks, be sure to stop by for a brew sometime. :guinness:

 

[bcarso]

That's a great idea---I've been going nuts with a remote as one by one the frequently used buttons get unusable. And I'm not one of those model consumers who change TVs and cars every two years.