conductive rubber keypads, again

[Tmoose]

An eng-tips search was only moderately helpful.

My harbor Freight digital torque adapter sat unused for several years in the house.

When summoned into service a few days ago it remained dormant.
The OEM offshore battery tested great, but I put a new one in anyhow, with no change.

Upon disassembly I found the 5 button keypad was segmented black rubber, with each ( presumably conductive) rubber button positioned to bridge its own small collection copper circuits on the printed circuit board when pushed.
I gently cleaned the power button rubber contact and the matching copper on the PCB with 70% isopropyl rubbing alcohol.
It worked for a few button push on-off cycles and then blacked out again.

On the internet there are a few different recommendations.
1 - Rub a graphite pencil on the contact area of the button to re-carbon it.
2 - Stick a dot of aluminum flashing tape on the button contact area.
3 - Stick a dot of copper tape on the button contact area.

My question is, how bad a choice is the pencil trick likely to be?
Reliably sticking a small dot of metallic tape seems iffy to me.
And I don't know enough to dare jam metal against PCB circuits. First for fear of damage, and second for uncertainty of the metal foil's ability to conform and touch multiple circuits properly.

thanks,

Dan T

 

[BrianE22]

I've wondered how well this works:

https://www.goldplating.com/products/pcb-repair-kit

If you try it let us know -

 

[MacGyverS2000]

Here, use some of this...

https://www.amazon.com/MG-Chemicals-Carbon-Conductive-Pen/dp/B01LZX06PL/

Pencil "dust" will just float all over the place and not stick where you need it without a binder of some form.

Dan - Owner

http://www.Hi-TecDesigns.com

 

[3DDave]

I have an alarm clock with the graphited rubber that failed after 10 years. I used aluminum sticky tape to repair. That was about 20 years ago. Still works in basically daily button pushing. It's not a high-current application so just bridging is good enough.

In another case, a remote for a projector, the graphite layer was rubbed off the power button as an exact match to the circuit. It was at work and it got funnier and funnier as people would twist every which way as if the remote was just not pointed correctly. I decided to take a look when users started to climb on the conference room table to push the power button -and- the battery in the remote had been changed several times. I guess no one noticed that the integral laser pointer worked just fine, indicating the battery was no problem. Put a piece of aluminum tape on the power button - problem solved. I doubt the projector is going to last 20 more years though.

That latter is probably what happened to you Tmoose - moving the button even a fraction of a millimeter allows the remaining carbon to touch the edges of the circuit. Disassembly and reassembly just changed the location a bit.

 

[hendersdc]

Silver conductive ink is another option: [URL unfurl="true"]https://www.alliedelec.com/product/gc-electronics/22-023/70159738/?gclid=EAIaIQobChMI_fTnlPW_5QIVQSCtBh29SgVNEAQYASABEgKb9vD_BwE&gclsrc=aw.ds[/url]

 

[waross]

I haven't tried this, but it would be my first try.
Most SUVs have an electric heater in the rear window.
Many of the heaters are powered by a flexible cable that is glued to the heating strips on the glass.
Any well equipped windshield repair shop will have conductive glue to repair the heater connections if they come unglued.
A thin coating of that glue may work.

Bill
--------------------
"Why not the best?"
Jimmy Carter