DMM probe repair - Page 1
Forum section: electronics / repair

author: najrao
author_rank: Regular Contributor
timestamp: September 23, 2019, 12:51:12 pm
content: I know I am asking to have my head chewed, but what else could I have done?I have only one pair of really good Fluke probes, all other dozen or so ones are cheap junk. So the good ones take a lot of beating.Even Flukes kick the bucket after a year or two. So did mine, both red and black going open circuit between their respective ends. Both the same way,insidethe meter end. Could simply pull the wire ends out. Had to salvage them.So Idrilledthrough the tops, 1.5mm dia and enough deep to reach and penetrate the brass thing inside, and another 2.0mm in this latter. Cleared the plastic out at the top to 5 dia by a flat drill to let the soldering iron tip to enter.Then drilled 1.5 dia through the barrel for wire entry. Enough deep to just let me see the newly skinned wire end nice and properly sitting in the blind hole.Doused in home made rosin flux, and applied 60W of 350C for 5 or 7s by soldering iron from the top, feeding solder as it melted. Nice joint.The plastic softened some temporarily, but got hard again after cooling downCapped the gaping hole with silicone putty to insulate back. Bingo! Probes back in service, good for another year. I can do this all over again then.Sorry, no pics. Shouldn't need any.

author: ferdieCX
author_rank: Regular Contributor
timestamp: September 23, 2019, 02:17:28 pm
content: As you said, repaired test leads could be quite dangerous.I have myself repaired Simpson 260 "inverted banana" test leads, but the meter is anyway not CAT III compliant.If you want to have something that could be more or less safe, I would try new connectors like these oneshttps://www.conrad.de/de/p/sks-hirschmann-las-s-w-sicherheits-lamellenstecker-stecker-gewinkelt-stift-4-mm-rot-1-st-736214.html

author: tooki
author_rank: Super Contributor
timestamp: September 24, 2019, 04:02:03 pm
content: Quote from: najrao on September 23, 2019, 12:51:12 pmWhy ghetto-rig something safety-critical, when sheathed banana plugs are easily purchased, as ferdieCX said??(FWIW, Pomona is the company that makes Fluke probes, and you can get sheathed banana plugs from them. But I like the ones from Stäubli best.)

author: mzacharias
author_rank: Frequent Contributor
timestamp: September 24, 2019, 06:31:41 pm
content: The original is press fit and held in place by (I suppose) adhesive inside the strain relief. The wire actually only presses against a cutout on the top side of the 4mm plug.So a bit of adhesive on the wire insulation before shoving it into the strain relief, maintaining pressure on the fit until the adhesive hardens, should do the trick.Anything you can do to maintain the pressure against the plug shaft would be safe enough - the question then becomes your level of confidence in it going forward.I would still just replace the test leads; the question of the probes would always be in the back of my mind.

author: najrao
author_rank: Regular Contributor
timestamp: September 25, 2019, 03:10:23 am
content: The original is press fit and held in place by (I suppose) adhesive inside the strain relief. The wire actually only presses against a cutout on the top side of the 4mm plug.Really? Have you actually sighted this? I have difficulty in believing that such design would pass muster at any reputable manufacturer. Weld, crimp or solder (in order of preference) would be needed for reliable joint. Simply pressing the wire copper against a brass fitment, and expecting to retain pressure by 'press fit' of the insulation to a plastic barrel, would border on the absurd. The wire core can still slide inside the insulation, and there is no compliance in the joint to retain pressure. The wire end bearing against the brass would tarnish over time and cause poor conduction across. Were this a Chinese product, eev bloggers would have employed choice expressions which I cannot put down here.Anything you can do to maintain the pressure against the plug shaft would be safe enough - the question then becomes your level of confidence in it going forward.I would still just replace the test leads; the question of the probes would always be in the back of my mind.Good advice. Thank you.