Agilent 54622D carbon pad restoration
As I said in a previous post, scrubbing / cleaning the carbon pads again with IPA did not help the conductivity, nor did it even remove much of anything. I say "again" because when I got it several years ago I did the same cleaning. That being said, I tested the keys again after cleaning this time and they did not function any better. They all worked but needed to be pressed "hard".
Taking a look at the pads under the microscope, and comparing them to new pads on a comparison keypad removed from a remote control that was never used, it was clear that a crusty layer needed to be removed. I decided to gently use a 600 grit wet sanding paper. Don't picture Magilla Gorilla with an electric belt sander now!
After the first specks came off (see pic), I cleaned the pad with IPA and it looked much better. I then tried rubbing again with the same light touch, but nothing more to note came off. You would have to scrub a lot harder to get anything more off - the pads are pretty tough - but after the first specks come off there is no need to do any more. And that is good because you are removing the crusty film and nothing more. In other words, these pads are not delicate.
You can check the pics - before and after. Also included is a pic of a good pad from a remote control. The Agilent pad is now has a much smoother surface and presents much more surface area upon a light press of the key.
The carbon pad is ~0.5 mm thick. I tried to measure any difference in thickness before and after the light scrubbing, but I could not detect any measurable difference with my micrometer. And certainly with the naked eye it looks as if nothing is different in the thickness. You could do this many times before you would even measure a difference with anything available to the average hobbyist. The amount of crusty material that comes off is extremely small, and after that the 600 grit wet sanding paper does little more to the pad.
Yet, it makes the pad work nearly like new. The buttons respond as any other "newish" gear I own does, with the slightest push on them. I will look at these buttons in a year (remind me if I forget), and we'll compare the condition of the pads.
*sigh*
Yeah... this is exactly what I was expecting.
You got lucky on this one; the carbon matrix on THIS KEYPAD is thick enough to suffer this attack. SOME silicone membrane keyboards are NOT made this way; even 800 grit will wipe the carbon off down to the rubber with just a couple swipes.
THAT is why
I only recommend a Q-tip dipped in alcohol; it is MORE THAN ABRASIVE ENOUGH to properly clean the glazing off any carbon pad, yet gentle enough that it takes real Magilla Gorilla action to do real damage. If you had
taken the care to observe observed before & after with magnification the last time as you did this time, and scrubbed a little longer with the Q-tip, you would have achieved the same results with much less chance of doing damage.
You're not the only one here who uses magnification to double-check his work.
It is SO easy to permanently destroy SOME examples of this type of keypad; abrasives simply are a bad idea as a rule of thumb. There's a difference here; and that lies in the fact that what we recommend here can be seen by complete noobs who may NOT have our experienced, cautious hand when applying such methods.
mnem
Please, for the love of little kids & kitty cats... learn from my mistakes, don't repeat them.