Cleaning Button Contacts: Siemens 820 control

andrewmawson · Feb 15, 2019

My 820T control sat unused for ages, and the control panel buttons can be a bit trying at times, needing a very firm press, resulting in not infrequent missed numbers.

Probably just need to clean the contacts - has anyone delved in as far as the buttons before - are they capacitive, or conductive pad, or even individual soldered on buttons? I had to re-seat the ribbon cables from the button matrix to the mother board last year when some rows didn't work at all, but I didn't get in as far as the buttons themselves. The card cage seems to be bolted to the front panel where the buttons are but what parts from what isn't immediately obvious.

. . . . fore warned is fore armed . . .

any help would be appreciated

Pathogen · Feb 15, 2019

If the actual contacts are mechanical they can be cleaned. If the switches are membrane, they need to be replaced.

andrewmawson · Feb 15, 2019

Pathogen said:
If the actual contacts are mechanical they can be cleaned. If the switches are membrane, they need to be replaced.

Well I suppose that's really why I'm asking the question, to see if they are a repairable technology.

By the way membrane switches often CAN be repaired if the problem is that the little conductive element is worn away. There are silver loaded paints that come in special kits. The silver paint is delicately painted on the pads and allowed to dry, restoring the key function.

In this case I doubt if they are actually worn away, the machine only has 500 hours on the clock !

jmullett · Feb 18, 2019

I have a Sodick EDM that has mechanical keys with the membrane element on the underside that make contact with a circuit board. I've had great success rubbing a bit of #2 pencil lead on them and they work again for a couple of years before I have to do it again.

adama · Feb 18, 2019

Pencil lead can help, but a going over the tracers with a good old steadler eraser can also work wonders. Key thing clean them first, takes very little dust - dirt to stop membrane switches.

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