Oxidation on oscilloscope probe compensation lead - Page 1
Forum section: electronics / testgear

author: MoreAxes
author_rank: Newbie
timestamp: March 04, 2024, 03:09:59 pm
content: Hi! I recently purchased a Rigol DHO924S and am currently learning how to use it (this is my first scope). I just noticed there is some oxidation forming on the probe compensation ground lead. I'm almost certain both leads were nice and shiny on first contact.Is this normal or am I using the oscilloscope wrong somehow?

author: Zenith
author_rank: Frequent Contributor
timestamp: March 04, 2024, 09:50:19 pm
content: It isn't normal and it's the sort of thing I'd expect to see on older equipment which had been kept somewhere damp, in which case I'd also expect to see it on the BNC connectors etc. I certainly wouldn't expect to see it on a new and fairly expensive piece of equipment.Furthermore it's on the entire surface. It's hard to imagine, but is it possible the terminal has come into harsh chemicals somehow? If so, why only that one?It looks to me as if the coating on the terminal is faulty.You can clean it off and put up with the possibility of it coming back. I'd guess you wouldn't have any problems with it, but it just shouldn't be there.Or you can complain to the dealer and be put to the trouble of returning it. They might clean it off and return it to you.I'd say getting in touch with the dealer and describing the problem would be a good first step.

author: MoreAxes
author_rank: Newbie
timestamp: March 04, 2024, 11:02:40 pm
content: There definitely weren't any chemicals spilled on it, even water. I'm extra cautious about this stuff. However, I actually asked this question in another "forum" (a facebook group, sorry not sorry), and the response I got was that this is actually normal, and due to the difference in material between the two terminals. The positive terminal is soldered onto the PCB and thus most likely nickel coated copper, whereas the ground lead is likely iron based with some sort of easily-oxidizing coating.To support this, I took a screenshot from EEVBlog's video on the DHO800. The terminals are also different looking there. I suppose one outstanding question could be why is the difference so strong in my case but not in the video? Although there's many contributing factors there, chiefly different lighting conditions and the black front panel of the 924S. I was shining a strong flashlight at the terminals in my photo to highlight the difference; compare with the photo I took just now without any direct light on the scope.Still not sure if that's conclusive, but I've been using the scope for a while today and at least it doesn't seem to be progressing. I had no contact spray on hand to see if it helps, but I ordered some and will try it when it gets here.

author: Zenith
author_rank: Frequent Contributor
timestamp: March 05, 2024, 02:33:56 am
content: This business about the calibration terminals being different metals and corrosion on the earth terminal being common, is something I've never come across. I've got a Siglent scope I've had for four years and it shows no sign of it. I haven't heard of anyone else having the problem.I suspect it's something that won't affect anything you do with the scope and it can be ignored as a minor irritation.Nonetheless, I think you should raise it with the dealer, because they are handling these scopes all the time, and it may be a known problem caused by a bad batch of terminals.

author: MoreAxes
author_rank: Newbie
timestamp: March 05, 2024, 07:44:49 am
content: I think it might be specific to Rigol rather than concerning all oscilloscopes. Here's a video where a guy shows how to compensate probes on a 1054Z:It seems like the leads are also slightly different there, and the 1054Z is ancient at this point, so maybe it's just something Rigol has been doing.Actually I've just had a look at the photo on my dealer's website, and it also shows that same difference:https://rigol.com.pl/pl/p/12-bit-Oscyloskop-RIGOL-DHO924-4CH-250MHz-1.25GSas-seria-DHO900/564.So I think that's conclusive at this point.

author: coppercone2
author_rank: Super Contributor
timestamp: March 05, 2024, 08:16:56 am
content: needs grease on purchase and maintence.

author: ebastler
author_rank: Super Contributor
timestamp: March 05, 2024, 10:47:01 am
content: The difference in appearance is normal, and no oxidation/corrosion is involved. The ground connector is a bent-up piece of the scope's metal enclosure, while the 1 kHz signal connector is a separate, soldered part. Different metals with different surfaces, but both are in good shape.See this photo from Dave's teardown for example:https://www.flickr.com/photos/eevblog/53165527759/in/photostream/

author: MoreAxes
author_rank: Newbie
timestamp: March 05, 2024, 11:56:50 am
content: Thanks, that just about settles it for me!