How To Repair Carbon Conductors Under Rubber Keypads

Ok so everyone has a pc keyboard, label printer, tv remote, garage remote, or video game controller at home. What do all of these share in common? Well most if not all use black circular carbon conductors underneath the rubber keys to complete a circuit when they are pressed, performing your requested action.

I have an issue now... What do you do when those black carbon conductors begin to wear out do to years of usage, and continuous pressing? Well the likely solution would be to chuck the device away, and buy a new one! Wrong...

There are apparently conductive paints available, conductive pens, goos, stickers of some sort, and homemade foils you can use to supposedly restore the keys. Now from what I read some of these are gimmicks, and do not hold up to continuous usage, or don't work at all.

So I figured I'd create this thread since many of you have highly intelligent minds, and could potentially offer me the best solution to repair/renew black carbon conductors under rubber keypads. That will hold up to the pain of multiple presses, and massive usage. & no I don't want to cut the carbon conductors off a spare keyboard, or calculator and glue them on my faulty ones. As that could mess up timing in things such as a video game controller due to height issues.

If you know of a rock solid way that can withstand a beating like it stole something let me know! Links would be good, homemade advice, or whatever you can offer. I need a long lasting solution specifically for some old video game controllers I use on my pc that they do not sell anymore. The keys on the controllers have to withstand a pounding! I also have tv remotes I would like to renew that have buttons you have to press so hard just to get them to work, as well as other old video game console remotes [Nes, Snes, old stuff like that].


Thanks

 

When I had a issue with an old game controller, I pulled it apart and used 90% alcohol to clean the carbon pads but was doubly sure to also clean the electrical contacts the pads are pressed against. Seemed to work for me but it is not a long term solution. Maybe Deoxit on the electrical contacts would do a better job.

 

That's not the issue, although I always do that first. I'm talking about completely remaking, or fixing the black carbon conductors under the keypads. With anything that will last a very long time, years even if possible.

 

Hi Super,

Just a thought: Haven't had many keyboards for PCs open lately. But TV remotes use a "carbon" looking "Grid" under each key and the key has a conductive substance that presses on the grid. Mine have always been the loss of conductivity of the key substance. Probably a manufacturering fault. Never had any luck cleaning or getting those to work except to add a foil disk to the key. Not worth the trouble if there are a lot of bad ones. One or two may be worth it. You can test the contacts with your ohm meter.

Good Luck, Jim

 

Long time ago I remember seen this kind of paint that were used to "repair" the carbon surface of potenciometers and or the black mask in the old TV screen vacuum tubes, maybe you can still find it in an old fashioned electronics store, it was an small glass container and a little brush (like the ruber glue applicators).:-o

 

how about rear window defogger repair paint? seems like it should work ok.

http://www.amazon.com/Permatex-15067-Window-Defogger-Repair/dp/B000HBI9YQ

 

WHY THE DIFFUCULT PASWORDS MAJOR GEEK? who cares..

as for the FIXING CARBON CONTACTS in keyboards, amps..

USE A ****IN PENCIL. try a soft brand

rub it on the contact.......its CARBON

don't use some exspensive spray

USE ACETONE... to clean the dirt of
and a a can of air spray... let it dry
rub on the pencil shavings.....whalla.......

 

How can carbon from a pencil just stick?

 

Hey Superstar, I used to design multilayer printed circuit boards and the board makers have several different conductive surface finishes available to print or to paint on the surface of non conductive substrates. Many TV remotes were fixed by me using a coating I never knew the name of and a very fine paint brush plus a lot of patience under a surface mount microscope. On a TV remote the fix lasts about 2 or 3 years depending on usage so it is not permanent. The coating from PCB makers is the best solution as they use coatings not generally available to the public and usually they use the best solution so that it won't compromise the quality or reliability of their PCBs.
I am not sure where you are but in Australia we used to use Entech Electronics in South Australia or in USA Bare Board Group or Amitron or US Circuit Inc. We also used to use a big company called East Coast Circuit Boards that were very good too but I couldn't find them so they may have gone out of business. Contact a PCB manufacturer and ask if you can buy a small amount and don't forget to ask for the correct solvent as they often use hard to get solvents (often meaning very toxic so be careful)

Here is a link to a conductive coatings supplier but just a tip. Try not to use silver as the conductor unless it says non tarnishing as silver oxidises turning black and then becomes high resistance

Just had another thought you used to be able to buy conductive pens for repairing rear window demisters and these were on sale in autoshops. Maybe try that too.

Good luck :major

 

Great reply JHoffa, any new suggestions though? That link you posted shows more of the silver based paints. There is carbon, however I don't know how good it is. I notice they sell a lot of paints on eBay have you seen any of those?

 

Never tried on ebay as I was head of the printed circuit board department in R&D for the major German global autoparts company. When I wanted stuff like this I would simply ask one of our suppliers to give me some and it would always come as several little bottles labelled as cleaner, activator, conductive ink and solvent. It didn't usually have the proper name on it and I can't remember any names anyway as I have now been out of the job for 12 years. I do remember one type I used had to have activator and also then be exposed to ultra violet light for 10 minutes in order to harden and this was cyanoacrylate based and had a very toxic vapour rolleyes
Most of the commonly available ones are either solvent based or epoxy based and these are a bit easier to use.
I used to get asked by senior managers and directors to repair their remotes quite often and had varying degrees of success but no outright failures :cool

My best suggestion would be to seek out the pcb manufacturers that make keyboard and keypad pcbs as well as ordinary pcbs as they will already have the ink chemistry on site so then it will just require a bit of negotiation to hopefully get some. If they have to get it in especially then they won't be interested as they have better ways to make money :major

I have had to use silver based inks before and although not ideal it still lasts for a couple of years with medium use or if it is the channel changing button about 12 to 18 months

Good luck and remember to heed any warnings about breathing toxic fumes or spilling on your skin. Some of the ink chemistry systems are very nasty chemicals indeed. For this reason alone the pcb companies may decide not to sell you any ink in case of liability linked to them for supplying very toxic industrial chemicals. So when you finally find some company with the ink you will then have to convince them you will be using it safely :major

I used to get all my supplies from pcb companies based in Australia, Malaysia, USA and Taiwan and as our company was spending many millions of $$$ every year with these companies, they were always eager to earn extra brownie points by being as helpful as possible

 

Well I've found stuff like this, couple years back I found some cheaper stuff.
Guess it's not on eBay anymore... I'm wondering if any of these would do.
To be honest I need them for some vintage arcade controllers that will undergo
heavy use over time. I don't mind purchasing this, or something like it if you think it's legit.

http://www.ebay.ca/itm/Conductive-Carbon-Paint-1ea-30-gram-bottle-with-brush-/280642344770?pt=LH_DefaultDomain_0&hash=item4157965742

http://www.ebay.ca/itm/Caig-Conductive-Silver-Paint-in-a-PEN-USA-Made-bus-fix-fast-ship-circuit-writer-/171005604794?pt=LH_DefaultDomain_0&hash=item27d0ba73ba

http://www.ebay.ca/itm/AQUADAG-CARBON-PAINT-ARCADE-MONITOR-TV-CRT-CATHODE-REPAIR-SPARES-30-ML-BRUSH-/261225440206?pt=UK_Sound_Vision_Other&hash=item3cd23fe3ce


Funny a little off topic, someone said use a pencil! I used to use graphite shavings from pens
and mix them with a bit of good Castrol Motor Oil to lubricate computer fan bearings. It would actually work out
pretty well. Until I found bearing lube on the internet, which is a bit hard to find for fans.

 

I've just fixed an Amstrad CPC 664 keyboard by using the conductive silver paint, it works really well.

 

Try the foil tape used to seal seams in your home ventilation ductwork. Cut out just enough to cover the rubber button and carefully apply it. It comes with an adhesive backing and a conductive aluminium side. Seems to work well. And much cheaper than all other commercial kits.

 

One of the advantages of silver is that silver tarnish is conductive.
https://www.finishing.com/347/57.shtml

 

The drawback of using a pencil is that it's rather "loose" and can potentially close the circuit constantly. Also, it may not wholly be the pads, it could be degradation on the circuit side.

Years ago I found gold plated flex circuit ribbon/card for my old school Atari 5200 controllers. Most likely the last ones they'll ever need...