Cleaning carbon/metal contact pushbutton switches?

Thread Starter

KMoffett

Joined Dec 19, 2007
2,770
We have a sputter coater that has a bunch of PCB mounted push button in the front panel. The complaint is that they don't work. The Physicist contacted the company, and they said that these switches are obsolete and no longer available from the OEM manufacturer or any others. Pictures from sputter coater company attached. I checked the in-circuit contact resistance. All measured ~1.5-2MΩ when open. When initially pushed, the resistance drops a little. Anywhere from ~1MΩ to 500KΩ. With a lot of forceful pushes, the resistance can drop to anywhere from 50KΩ to 5KΩ. But that doesn't last. I assume with a carbon contact that the 5KΩ is a good contact. I see a lot of posts out there about cleaning rubber/carbon/metal contacts. But they are all disassembled. I thought maybe spray De-Oxid might work, but I don't know how it would affect the carbon.

Any ideas or experiences?

Ken



108 or 108A old  push momentary button parts  001a-1.jpg Button with sticky back foam on both sides fix .jpg
 

MaxHeadRoom

Joined Jul 18, 2013
19,029
In many cases the conductive surface wears away, in this case the only way to resolve it is find some substitutes.
Otherwise you could try a type of contact cleaner that does not leave a lubricant residue.
Max.
 

Thread Starter

KMoffett

Joined Dec 19, 2007
2,770
They are all PCB mounted behind the front panel and I'd rather not try to disassemble them. But I took another look, and it might be possible to disassemble them. (attached) My fear is that in trying to release those little plastic spring clips on the sides will result in breaking the old plastic.

Ken

DSC05666.JPG
 

MrSoftware

Joined Oct 29, 2013
1,562
I can't say whether the problem is worn out parts or just dirty parts, but if you want to try a spray cleaner I've had good luck with the CRC electrical contact cleaner. Just be sure to remove power before using it, and don't power it back up until you're 100% sure it's all dry (it dries really fast):

https://www.amazon.com/CRC-05103-Electronic-Cleaner-11/dp/B000BXOGNI/ref=sr_1_2?crid=1A3YJXPPF7A27&keywords=crc+electrical+contact+cleaner&qid=1559840166&s=gateway&sprefix=crc+electrical,aps,169&sr=8-2
 

djsfantasi

Joined Apr 11, 2010
5,591
Before you disassemble them, have a Plan B. Gather some temporary push buttons that can be hacked onto the control board if the patient dies during the operation.

I’d only do one at a time. And since you’ve identified that they have plastic bodies, gently warm them before disassembly.

If you want a Plan C, identify replacement switches in advance. If you can purchase them with a generous return policy, do so before starting an operation.

It looks like you have barely functional switches now, so if they break, you’re not too bad off. If the repair works, congratulations. Now return the unused switches.

And always remember, if Plan B doesn’t work out, there are 24 more letters in the alphabet!
 

Thread Starter

KMoffett

Joined Dec 19, 2007
2,770
There no suitable replacements. The buttons are sort of oval...rectangular with half rounds on each end. Like the "Autoset" in the upper right corner: https://www.tek.com/document/online/primer/xyzs-scopes/ch4/oscilloscope-systems-and-control
And there 13 of them. Foot print is a 4 pin diamond orientation not the usual 4 pin rectangle. As soon as the contact cleaner gets here, I'll ask if there are any of the buttons that are never used. Plan "D". ;)

Ken
 

Thread Starter

KMoffett

Joined Dec 19, 2007
2,770
Problem solved. Removed the PCB from the front panel. Very, very, carefully squeezed the two pairs of fingers the hold the button to the switch base. I did not break any. :) Removed the little rubber dome that holds the carbon contact cylinder. Cut a small sliver from an eraser to clean the metal contacts. Also, hit the metal contacts with CRC 03130 QD contact cleaner. Reassembled. The Physicist just tested it, and all buttons now work. Very delicate work. I can see why the company would not want to work on it.
Thanks for all the input.

Ken
 

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