are some wires bad? Random corrosion in cable harness - Page 1
Forum section: electronics / repair

author: coppercone2
author_rank: Super Contributor
timestamp: October 28, 2022, 06:20:32 am
content: I have some kind of brand 5110 Voltage Calibrator I am trying to repair. I don't know what it is, maybe Digi-something. I got it many years ago.The outside of it has 4x transistors, some of which are 2n26422.Anyway, they are mounted with a cable harness that goes into a molex thing (like a motherboard power connector).Two of the transistors (on each heat sink block) seem to have blue corrosion from the heat shrink under the transistor lead to the plastic connector body.The capacitors are not leaked, and they are on the other corner of the PCB (its like a 9x11 size unit).I am having trouble understanding why randomly 2 wires in a cable harness might have corrosion. This thing does not have batteries, the caps are far away and they don't looked like they leaked. It would be hard for corrosive material to even get into the transistor heatsink module on the back. I don't think it could wick up the square pin into the wire, its not helium 3. It would be hard for the corrosion to reach the transistor unless you dipped the unit into a pool of something standing on the back side, if anything dripped on it, it would likely not get into the well heat shrinked lead. I had to cut it off with a exacto. The board looks very good, the silk screen is in tact.Has anyone seen wires just spontaneously corrode like that? Something with the insulation maybe? like the pigment? It looks like the orange and yellow wires have it.

author: alm
author_rank: Super Contributor
timestamp: October 28, 2022, 09:11:10 am
content: I haven't, but a picture is worth a thousand words, especially if those words are vague like "some kind of brand" "molex thing".

author: jonpaul
author_rank: Super Contributor
timestamp: October 28, 2022, 09:38:00 am
content: Certain 25...60 yrs old plastics decompose and emit a corrosive liquid or gas.A lot of WWII and Cold War electronics have such corrosion.Alchol and perhaps vinegar or baking soda may remove and clean it up.After any fluid flush, we use 99% ISO alcohol and then a gentil heat to remove any H2O residue.Please post pix!Jon

author: cvanc
author_rank: Frequent Contributor
timestamp: October 28, 2022, 11:22:53 am
content: Yes, pics please.Lots of old transistors have corroded leads. They don't need help to do it from the outside world, it's spontaneous as far as I can tell.

author: Circlotron
author_rank: Super Contributor
timestamp: October 28, 2022, 11:36:47 am
content: Quote from: coppercone2 on October 28, 2022, 06:20:32 amProbably a Molex Mini-Fit Jr.

author: coppercone2
author_rank: Super Contributor
timestamp: October 28, 2022, 04:34:07 pm
content: well imagine if its just one wire, same color, in two different cable harness going to external transistor. Both yellow color.On both ends of the wire, near the connector and near the transistor. Since there are 8 wires per harness, it seems odd that only one of them is corroded in each one.I did not strip the wire yet but I imagine the corrosion runs down the entire length of the wire, since it shows up on both ends.

author: coppercone2
author_rank: Super Contributor
timestamp: October 28, 2022, 04:41:58 pm
content: nothing to take a picture of anymore because I scrubbed it while trouble shooting, but of course its not worknig. maybe if i strip the wire to expose the interior it can be done, but I don't want to mess with it more because I need to take it apart to remove the connector from the board hole, and right now this is going on my to fix later shelf in pieces before it gets permanently damaged, not a pleasant repair

author: coppercone2
author_rank: Super Contributor
timestamp: October 28, 2022, 05:14:46 pm
content: that POS had a transistor to3 that body was connected to two ring lugs attached to a single wire, of course one of the rings was fractured and the other ring, despite being bolted to the transistor, had 0 continuity.So you double connect something and it still breaks.It was working with a ring lug that was fractured and the wire was making a infinitesimally small contact point with the wire, part of the crimp, and the rest of the crimp. If you blew on it, the compliance light went on. The electrical contact was like the knife edge of a scale with a broken crimp. unbelievable