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I have an old transceiver. I have a problem where ocassionally the received signal will drop out when switching from transmit to receive. I've narrowed it down to the transmit/receive relay. When bench-testing the relay, it "clicks" over to receive, but shows a very high resistance. The contacts aren't visibly corroded or damaged. I have heard that the contacts may have to be cleaned - what's the best way to do this? Are there any cleaners that should be avoided?

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  • $\begingroup$ Note, many contact platings can include cadmium, indium, palladium, mercury, etc., even today and long into the foreseeable future. $\endgroup$
    – rdtsc
    Commented Oct 25, 2023 at 17:55

2 Answers 2

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Cleaning relay contacts is usually done mechanically. Use fine grade garnet paper (not generic sandpaper -- it can leave conductive dust behind), fold a strip in half and put it between the relay contacts, push the contacts together, and pull the paper out. Repeat until done.

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  • $\begingroup$ Garnet paper is sandpaper, of a type. However, it's one that's getting hard to find these days. It's not friable like aluminum oxide (the much more common type of sandpaper) and so it cuts slower and wears out more quickly. I imagine the name aluminum in aluminum oxide can lead one to believe it's conductive, but it's not really, it's a big ingredient in ceramics. Aluminum has a resistivity of 2.82 × 10^-8 Ω·m, where aluminum oxide has a resistivity of 1 x 10^16 Ω·m. $\endgroup$
    – WPrecht
    Commented Nov 12, 2013 at 20:13
  • $\begingroup$ @WPrecht-AB3RY - I clarified the difference. Google shows garnet paper available from Amazon and Woodworker.com. $\endgroup$
    – Pete NU9W
    Commented Nov 12, 2013 at 20:30
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To follow up on my comment to Pete's answer, the contacts probably have some oxidation (tarnish) on them, depending on the metal involved.

What you don't want to do is gouge up the contact surface with something that's too abrasive. You just want to clean the surface and restore conductivity. Rag based bond paper works well (a crisp US dollar bill, for instance). Insert the paper, gently hold the contacts together and swipe out the paper. Should only take a few swipes. If the contacts are plated over a base metal, any cleaning process will have a limited number of uses as the plating in these cases is very thin.

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