whit3rd wrote:
On Sunday, November 18, 2012 7:25:15 AM UTC-8, BQ340 wrote:

On 11/17/2012 10:00 AM, Pete C. wrote:



^ This. Whenever strange issues start to crop up with a machine that's
fairly old, powering it down and unplugging/replugging every connector a
few times wipes oxide buildup off the contacts and usually solves the
problem.


Exercising sockets is a valuable technique.


Yes, I have experienced that too, especially with memory cards. I rub a
piece of regular copy paper on the card contacts, it acts like like very
fine sandpaper.


That's called burnishing the contacts, another valuable technique.



I think though what really happens is the oxide is on the contacts in
the socket not on the gold card edge, but it works.


Gold isn't immune to oxidization (it forms an oxygen monolayer
spontaneously), but the film is thin and it doesn't grow.

Tin also oxidizes, but a thin layer of tin oxide is conductive (it's indium/tin
oxide that makes the transparent electrical connections for your LCD display).

Most important, is that a speck of dust or a film of oil or moisture can be submicroscopic
and still impede the low voltage connections in a computer. So, disturbing the
surface by mechanical wiping (like, when you loosen and reseat a memory module)
fixes that entire class of problem.

I remembered this problem when a friend complained that the Cal Controls
controller on her glass furnace was giving thermocouple failure faults.
Various people had said to buy a new controller but as I have a Cal
controller I was aware that the guts of the controller can be prised out
of the panel mount enclosure, I presume to allow easy replacement when
banks of them are fitted such as in plastic extruder lines. As I had
mine apart to fit a comms module I was aware the PCB contacts were just
tinned and might suffer this problem possibly causing issues with low
level signals such as the thermocouple. I made a small pry bar to get
the guts out and re-inserted it a couple of times and the problem went
away. I've had the same happen on my controller more recently and
removing and refitting it cured the fault.