Tek P6139A 'Probe Rot' repair - Page 1
Forum section: electronics / repair

author: Gyro
author_rank: Super Contributor
timestamp: May 08, 2016, 01:52:15 pm
content: Has anyone else had problems with the rubber bodies of their P6139A scope probes dissolving from the inside and splitting?The resulting sticky mess is a pain to handle. I think it may be something to do with a lubricant inside the lead seeping and being incompatible with the rubber.Two have my probes failed like this now and my remaining probe and spare lead are showing signs of seepage.I've now repaired the two messy ones, I though this would be more difficult, I'd forgotten that with probe dismantled there is nothing of large diameter to prevent suitable sized heatshrink to slide over. The disolved gunk cleans off really easily with isopropyl alcohol. I used two bits of heatshrink of the same diameter, the first as a strain relief and a second shorter one after the first was shrunk just to reinforce the crimp area (see photo).The good thing is that after the repair, the probes are much nicer to use than before. They're more compact with less weight on the rear and a much better shoulder to get your thumb on when retracting the hook. So far, a definite win.I haven't seen the same failure yet at the scope end, possibly because that end gets flexed less, or maybe with the scope on the shelf they are 'up river'.

author: HighVoltage
author_rank: Super Contributor
timestamp: May 08, 2016, 02:31:14 pm
content: You mean TektronixP6139A?I have many of them and they are in perfect condition although I am using them constantly.May be there is a quality difference between the grey and black model?

author: Gyro
author_rank: Super Contributor
timestamp: May 08, 2016, 02:55:33 pm
content: Damn, did it again!Fixed.Yes could be, these are the grey ones, maybe a bad batch or rubber formulation.Edit: I think mine are earlier - they have a ridge above the ground sleeve that none of your grey ones have.

author: HighVoltage
author_rank: Super Contributor
timestamp: May 08, 2016, 03:44:36 pm
content: I have a few more of the black P6139A probes and it seems they all came out of the same mold.But my two grey probes definitely came out of a different mold.

author: Ian.M
author_rank: Super Contributor
timestamp: May 08, 2016, 04:11:53 pm
content: Rotting 20th century plastics, especially elastomers, are a major problem for collectors and museum conservators everywhere.The difference in the strain relief degradation at the probe end and scope end may simply be because you were unlucky enough to get a bad batch of the former (e.g. with excess plasticiser or incorrect mix ratios for the polymer) or it may be due to contamination from frequent handling.

author: Gyro
author_rank: Super Contributor
timestamp: May 08, 2016, 04:57:58 pm
content: Quote from: Ian.M on May 08, 2016, 04:11:53 pmThat was my first though, but they definitely rotted from the inside out - to the point of being runny in the middle (hence the assumption about cable lubricant).Edit: Whatever it is, it's very soluble in IPA.

author: Ian.M
author_rank: Super Contributor
timestamp: May 08, 2016, 05:36:46 pm
content: Even rotting from the middle can be due to contamination from handling - the well ventilated aerobic environment at the surface can slow the degradation. However I agree a faulty elastomer mix is more likely.

author: SeanB
author_rank: Super Contributor
timestamp: May 08, 2016, 07:53:45 pm
content: Careful of the rot though, it likely is a toxic blend of PCB plasticiser and other brominated flame retardants used to make the plastic flexible and flame proof.

author: wraper
author_rank: Unknown
timestamp: May 08, 2016, 08:02:17 pm
content: Might be that you cleaned them with some solvent at some point of time. Donno about these probes but I've seen this happening with screwdrivers. Clean once and it starts slowly rotting.

author: Gyro
author_rank: Super Contributor
timestamp: May 08, 2016, 08:38:42 pm
content: Hmmm, thanks for that comforting thought SeanB!I don't remember cleaning the probes with anything but they've been in service for a long time. I guess there is always the possibility of transfer of Fluxclene over the years.Yes, I've seen rubberized plastic go sticky for no apparent reason when left on the shelf, it happened to an IR temperature probe I had, the only solution was to strip it back to the plastic. That was never exposed to any cleaners. What happened to good old Bakelite.