Best contact cleaner for carbon contacts? - Page 1
Forum section: electronics / general

author: Skyfox
author_rank: Regular Contributor
timestamp: May 05, 2018, 12:26:20 am
content: Hi all,What's the best contact cleaner for carbon contacts? Or alternatively, what's the best way to clean carbon contacts? I'm cleaning the keyboard on one of my Commodore 64s (and have many more to go) and would like to take care of some of the keys that require a little bit of an extra firm press for the key contact to be detected. The board is carbon contacts and the keys are the rubberized carbon contacts. Would simple isopropyl on a cotton swab be alright or could that do damage? Thanks!

author: Electro Detective
author_rank: Super Contributor
timestamp: May 05, 2018, 02:04:08 am
content: If a damp soft wipe with a Q tip in distilled water doesn't work, I'll use non residue IPA/ isopropyl 'sparingly'being careful not to use much force or quantity as the adhesive holding the carbon contact may weakenor if the carbon contact is thin/cheap it may flake offi.e. go easy and don't get medieval on it, if the contacts are working ok again... time to walk away and on to the next item

author: Gregg
author_rank: Super Contributor
timestamp: May 05, 2018, 04:25:52 am
content: I used to restore contacts in calculators that used the rubberized disk for the key contact by gently cleaning with alcohol and going over them with a very soft pencil then gently blotting by placing the rubber sheet contact side down on a clean sheet of paper and pressing on the non contact side to remove excess graphite. Sometimes the fix would last longer than the original.

author: helius
author_rank: Super Contributor
timestamp: May 05, 2018, 04:38:05 am
content: The advice to use pencil graphite is a good one. There were some pencils made specifically for the conductivity of their graphite, such as the IBM Electrographic for machine-readable forms. There is also a type of conductive ink called "nickel print" that may be useful.

author: David Hess
author_rank: Super Contributor
timestamp: May 06, 2018, 07:48:55 pm
content: Naphtha (lighter fluid) is also a good solvent and is commonly used in "plastic safe" contact cleaners.

author: labjr
author_rank: Frequent Contributor
timestamp: May 06, 2018, 10:08:38 pm
content: If the keys still don't work well after you clean them, the carbon may be worn off of the contact.A guy who does synthesizer repair uses a conductive paint to repair the carbon contacts. The product is made by Chemtronics called CircuitWorks 2605. It's a bit expensive, about $20-25 from different sellers. You mix two parts and have to use it up within 2-3 days.You might ask him how well it holds up over time.https://youtu.be/gS5tnkgvE20

author: Skyfox
author_rank: Regular Contributor
timestamp: May 07, 2018, 04:56:18 pm
content: Thanks for all the info, everybody. So far all my cleaning efforts have turned up nothing. I started by wiping the board with distilled water, and that didn't help. Then I wiped the whole board with 99% isopropyl on a cotton pad, and that didn't work. Then I wiped each pad individually with isopropyl on Q-tips, plus gave a quick wipe to all the rubberized pads, and that didn't work. (Not super hard, just enough to get a mild gray tint to the swab.) Then I started testing resistance across the pins leading to each of the hard-press buttons and found they were 1.5Kohm or more, while the good buttons were down around 200 ohms. So I tried swapping the buttons around and found there was really not much difference in the resistance, leading me to think it's the contacts. Next I used a pencil with very conductive lead to scribble on the board contacts for the bad keys, and after putting it together for the 4th or 5th time it still made no difference. All those keys still need a little bit more force to make them work than the other keys.Someone over on the Lemon64.com forum suggested I use Keypad Fix, which is basically a conductive paint (and not as expensive as CircuitWorks), so I'll try that next. And with 6 more units with very bad keyboads, I'll probably need a lot of it.

author: Gregg
author_rank: Super Contributor
timestamp: May 07, 2018, 11:40:11 pm
content: Maybe posting a couple of pictures of the key contacts both sides would jog some memories of fellow forum members resulting in better suggestions.

author: eliocor
author_rank: Unknown
timestamp: May 08, 2018, 12:58:34 am
content: in the desperate cases, I glue* a small tinfoil disc on the keypad conductive rubber: never failed anymore!*) neoprene glue

author: Electro Detective
author_rank: Super Contributor
timestamp: May 08, 2018, 09:53:01 am
content: Quote from: Skyfox on May 07, 2018, 04:56:18 pmIt's time to roll up the sleeves, matePost some pics if you can, it may not be a carbon contact issue