On Sun, Nov 24, 2013 at 9:08 AM, Tom W8JI <[email protected]> wrote: > ... But all this tells me is that some silicone dielectric greases may not >> be abrasive. >> > > ... contact wear, which is not unusual for contacts that arc when > switched ... caused by the arc carburizing the grease into a > silica-carbide, which is a well-known abrasive.
Those switch contacts carried 5 VDC at a milliamp (at most!) to and from a CMOS interface IC (similar to BCD, but it wasn't) on the logic board of the computer that ran the machine. And I don't think that's enough to make anything arc, do you? :-) I wish I would have saved that switch that I greased, or took a good photo of it. The circle of grease around the contacts turned bright silver, almost white, with no visible traces of the underlying phosphor bronze contact base metal. And from the amount and appearance of the resulting "silver grease" perhaps the contacts had a heavier-than-normal thickness of silver plating. Whatever the case, I never expected to see what I did, and I'll never forget how the machine acted after so short a time, how the switch looked when I took it out, and how amazed we were. If that grease we had wasn't abrasive, I just don't know how else to explain what happened there. When I saw the silver-impregnated grease bridging between all the stationary contact fingers, and the odd way the machine acted, I assumed that the grease must have been carrying some current between several isolated stationary contacts. I don't remember checking to see if it was conductive; but as full of silver 'powder' as it became, it sure should have been. I would appreciate learning exactly what silicone dielectric grease that you successfully used. I currently use a clear liquid lubricant made by DeoxIT (S-Shield?) on wiping switch contacts. I seem to recall that WB2WIK said that white lithium grease was good on rotary switch contacts. I've never tried it. 73, Mike www.w0btu.com _________________ Topband Reflector Archives - http://www.contesting.com/_topband
