New lease of life for worn meter probes.

[davegsm82]

I had these old fluke probes laying around which had totally trashed pointy bits. They'd been filed back so many times that you could barely see the end of them when pointed at a board in use.

Since I do a lot of small SMD work I had the idea of making them really pointy and delicate.

So I have filed the points flat, drilled an 11x1mm diameter hole down the end and fitted 2 'pogo' pins from eBay. A pack of 50 costs less than 3 quid delivered and they are the perfect thing for this job.

Only downside is that they get damaged really easily, if the probe drops on the floor you can guarantee it will bend the pin. Fortunately they're cheap and you can just pull it out with tweezers and fit a new one in seconds.

   

[davegsm82]

Just realised that I should have perhaps posted this in the Test equipment category.

Doh!

[Mark Hennessy]

Not a problem - I can move it for you...

I thought I'd replied to this, but obviously forgot to click "Submit". Basically, I said something like "nice job, and a lot cheaper (and probably better) than Fluke's equivalent (the TL910)". I'll let you look the price up

[davegsm82]

...."Fluke's equivalent (the TL910)". I'll let you look the price up

By the Beard of Zeus! £62?

I should set up a business. Anyone got any old Fluke leads laying about?...

[Nick]

I thought I'd replied to this, but obviously forgot to click "Submit". Basically, I said something like "nice job, and a lot cheaper (and probably better) than Fluke's equivalent (the TL910)". I'll let you look the price up

The Pomona 6341s are pretty much identical and "only" half the price: http://uk.farnell.com/pomona/6341/test-l...dp/4135775

[Mark Hennessy]

Pomona have been a Fluke company for many years, and manufacture all Fluke-branded probes. The Pomona-branded versions are normally much cheaper.

Until recently, Fluke have been part of the Danaher corporation (along with countless other well-known brands, including Tek). Earlier this year, a spin-off company was created called Fortive, and Fluke are part of them now, along with many others: http://www.fortive.com/our-businesses/bu...-directory - no idea what this means for their future, but I really hope it helps Tek, who have seriously fallen behind in the oscilloscope market.

Meanwhile, we bought 3 or 4 sets of those Pomona probes, and they've been disappointing. With no provocation whatsoever, they've all gone high-resistance. By squeezing in the right place, you can change the resistance - suggesting the crimping didn't work. Eventually, I'll cut one open to see what gives. Oh, and the Fluke versions are also affected: http://www.eevblog.com/forum/testgear/fl...r-quality/

Hence my comment about Dave's version being better

[Alistair D]

In the days when I worked for a living my department used thousands of those pogo pins every year. The pogos we used had a tiny ball bearing between the base of the tip and the spring. The idea was that the ball rubbed between the tip and the barrel keeping the probe resistance lower. I have to say they were definitely much better than non ball variety.

When probe go high resistance it is usually due to dirt ingress. They can be quite easily cleaned by operating the probe a few times while immersed in IPA then a few times more upside down out of the solvent.

Al

[pamphonica]

Nice bit of lateral thinking, Dave. I like the idea of replaceable tips. Clever.

For those who are less handy with 1mm drills, I know it's still a lot (£25 incl VAT), but these probe kits by Keysight (Agilent/HP) are excellent. They are the same ones they include with their £1000 bench multimeters.
The very sharp tips can be clipped in place quickly if required. And I feel a lot safer than with Chinese probes. I use them on all my more recent bench and handheld multimeters.
The clip leads have two small clips and a larger clip for earth/chassis connection to allow single (red) probe operation.

http://cpc.farnell.com/keysight-technolo...dp/IN05806

Jeremy

[davegsm82]

Wow, those Pomona ones look like exactly the same as what I've come up with! maybe the body of the probes are a little smaller, but looking at the datasheet it would appear they are using pretty much exactly the same 1mm (0.04") pogo pins!

I couldn't justify spending that much on a set of leads, especially with the poor reports they receive here. I'll make-do with my creations.

The drilling of the 1mm hole is indeed a bit fiddly, however a decent pillar drill and a vice will actually hold it perfectly well for the operation, the copper of the probes is less inclined to let the drill bit skip sideways.

Dave.

[Mark Hennessy]

Yes, they are quite a bit smaller:

   

Time to open up one of them. This one had a resistance between plug and tip of anything between <1 ohm and infinity, depending on how you wiggled and squeezed it. Clearly something wrong...

   

Under the plastic, a brass rod has the wire crimped at the end. It's quite a decent wire, BTW, and as such I'll make use of it by attaching a spring hook or similar to the end.

At the other end, something else is crimped. But what?

The probe tip is removable, and you can just about see the end of it poking through the end of the metal sleeve.

It's hard to be sure, but it looks like the metal sleeve has broken away at the point it exits the brass rod. Next time I take one apart, I'll do it more carefully.

This isn't a brilliant photo, but best I could do in a hurry:

   

You can see the tube which I think was once the same as the tube you can see in the other part of the probe, crimped in place. And note the red plastic between it and the outer brass rod...

Note that the end of it wasn't quite as rough at first - I had a gentle "prod" before I took the picture.

I'm not sure how the plastic got there - perhaps it's just filling a gap that occurred? I assume these probes are injection moulded (polypropylene) before the grey soft-touch overmoulds are added.

Anyway, the interface between the two metals appears to be the problem. There is a good sub-1 ohm resistance between 4mm plug and the brass rod, but careful probing reveals a higher resistance between 4mm plug and the inner (stainless steel?) tube. To get to the bottom of that, I guess I'd need to file away a section of the outer brass rod and somehow open it up. Hmm. Maybe tomorrow...

Incidentally, I don't know which Pomona probe this is. From a quick look on the Farnell website, there are at least 3 possibilities. However, I'd assume they are all much the same, and possibly prone to this high-resistance failure mode. Of all the probes we bought, this is the only one that could be persuaded to go O/C - it's possible that someone bent it too hard and severed that internal tube. I will take apart another at a later date. Any suggestions about the best method? I'm considering a blow-torch!