TEKTRONINX P6139A shorted, metalic, Grow Metal Crystals? any definitive solution?


Miguel Work
 

Every year I have to clean the inside of the probe tip, there are some king of growing metalic short. I have 4 probes with the same problem

https://www.youtube.com/watch?v=f2jeixZCZPs


Roy Thistle
 

On Sat, Sep 11, 2021 at 07:08 AM, Miguel Work wrote:


there are some king of growing metalic short
Well... I watched the video... and I see you cleaned out the "socket" (on the end of the probe's coax), where the probe tip screws in.... you used alcohol.
Initially... you got a resistance of 0.14229 ohms? (That resistance measurement could be telling.)
We can't really see inside the "socket" to see what's in there... and to observe the phenomenon.
Metal whiskers can grow. It's a known problem; but poorly understood. (Often it is tin whiskers... but, other metals can also have this too.)
Dendrites can also grow: that is an electro-chemical phenomenon.

--
Roy Thistle


 

Miguel,

According to the TekWiki entry on the P6139 the cables have "a whisker- or dendrite-growth problem," the fix for which is to replace the cable. There is a temporary fix that involves running current through the BNC connector to burn away the whiskers, but it is only a temporary fix. I have avoided buying cheap P6139s on eBay for exactly this reason.

The literature on tin whiskers is fascinating and bizarre.

-- Jeff Dutky


Roy Thistle
 

Hi Jeff:
Well... in his video... he cleared the short by washing out the socket on the cable where the probe tip screws in... with a brush soaked in alcohol.
Did you watch the video?
Maybe it's not a "tin whiskers" problem?
--
Roy Thistle


 

Roy,

Ive watched the video multiple times. I admit that the resistance value he is seeing is not what I expect from tin whiskers, but I’ve only had one experience with them, and I did not try to measure the actual resistance of the short they caused (it was in a 2N2207, and I cleared the short by rapping the case on a hard surface. Since the mechanical cure “fixed” the issue I took it as read that the cause had been tin whiskers).

The method he used to clear the short is clearly not the method mentioned on TekWiki, but I struggle to imagine what else could cause the short, and return annually. You would think that if there were some environmental factor causing the short that it would cause problems with all sorts of other equipment, and to a much greater degree that with part of an oscilloscope probe that is protected by a screw thread.

It’s not clear from the TekWiki article where the tin whiskers usually happen in the P6139 cable. I had merely assumed that they occurred in an open space an either end, and could be cleared mechanically.

— Jeff Dutky


Roy Thistle
 

On Sun, Sep 12, 2021 at 10:50 AM, Jeff Dutky wrote:


but I struggle to imagine what else could cause the short, and return
annually.
Hi Jeff:
There is another phenomenon that causes observations like tin whiskers to occur... and that is dendrites: an electro-chemical process that is well understood, relative to tin whiskers.
I'm not claiming it's not a tin whiskers phenomena (or that that P6139As don't have a tin whiskers problem)... just that what I see on the video 'suggests?' it might be a dendrite problem.
Maybe that hasn't been considered before?

--
Roy Thistle


Miguel Work
 

Video is not mine, but I have the same problem that that guy
I use a needle to clean, scracth, the same area.
Ohms reading are the same, almost a short.

Some times I have used injecting current method, but about every year I have the same problem
Is a TDS5054 with four original probes, when I bougt it, secon hand, two probes were not working


Roy Thistle
 

On Sun, Sep 12, 2021 at 02:02 PM, Miguel Work wrote:


I use a needle to clean, scracth, the same area.
I have the same problem
Hi Miguel:
Yes. As to the first quote... I'd say that a needle is hardly a brush. And to clear metal whiskers (if that is what the cause of the near short is) ... a needle seems appropriate... and it seems a brush would not work. Yet, in the video, Mr. Aleksey Antonov uses an alcohol soaked brush.
That there is a problem with the P6139A probes does not clarify what the problem is. All we know is that it is observed that a short develops.
Have you tried the brush 'method' that A.A. used?

--
Roy Thistle


David Holland
 

On Sun, Sep 12, 2021 at 5:46 PM Roy Thistle
<roy.thistle@mail.utoronto.ca> wrote:
<snip>
... and it seems a brush would not work. Yet, in the video, Mr. Aleksey Antonov uses an alcohol soaked brush.
The one time I've definitely seen tin whisker syndrome, (old
potentiometer, had high voltage across it.) a brush would most
definitely work. The whiskers are amazingly fine. Matter of
fact, I think that's pretty much what I used to clean them out of the
potentiometer. (along with alcohol.)


Ed Breya
 

I have to ask. Is it only this particular probe that has such problems? If so, there must be something unique about the materials in the cable and connection. I'd guess the insulation plastic materials are releasing certain chemicals that cause galvanic action and eventually grow a short. Maybe the plating on the conductors has an effect too.

It seems that it is a surface-only effect since it can be readily cleaned off. This indicates the action needs something from the air too, like water vapor, O2, CO2, etc.

So, whatever the cause is, the main thing is to prevent or slow the action, so I'd suggest gooping the cleaned and dried connection with something to seal the joint surfaces where the stuff grows, and keep air out. A little bit of mineral oil may be about right, or vaseline, if high viscosity is needed to keep it from soaking out. You can use silicone grease sparingly. There are all sorts of fancy protective oils and coatings available, so there may be an ideal one for the purpose. If you can get some of that "Mom's Old-Fashioned Robot Oil," even better.

Of course, adding extra dielectric material in a line may have some unwanted effects, but should be very tiny, considering the joint gap dimension (which may be about zero if the ends mate flush). I'd guess you wouldn't be able to tell the difference.

Someone with several of these probes could do a controlled experiment, and treat one with some kind of goop, and then compare to the others over time.

Ed


Miguel Work
 

Hi Roy

No, next time I will try it and add some oil.
I will tray to make a phto with the microscope

Regards!