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Old 15th Feb 2016, 10:26 pm   #1
Station X
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Default Dodgy scope probes.

Am I the only forum member to have problems with the type of scope probe shown here?

The slide switch goes intermittent and eventually stops working altogether.

Is there a way of dismantling these probes to gain access to the switch? I know that the tip can be unscrewed, but that doesn't reveal the switch. It's possible they pull apart, but I don't want to break one trying.

Can anyone recommend better probes at a reasonable price?
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Old 15th Feb 2016, 11:07 pm   #2
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Default Re: Dodgy scope probes.

Yup.

The best advice with switched scope probes is to dump them, I'm afraid. The switches go iffy and it's also too easy to slide one unintentionally which is not good on high voltage things.

Additionally, even on 10:1 ratio, the bandwidth and the load on the circuit being probed are disadvantaged compared to a non-switched 10:1 probe.

Stick to the unswitched 10:1 jobs, and use a separate 1:1 on the rare occasions when you really need one.

One trick with scope probes is that although they aren't flat connected to 50 Ohm ports, you can use them in reverse on a sig gen to inject small uncalibrated amounts of signal without loading circuits much at all. You can also use them on the inputs of spectrum analysers. Their sensitivity makes up for the loss fairly well. These tricks are good for quick and dirty fault-finding.

Tek probes are good, but second-hand carry a premium beyond their true worth. HP ones are good too, but haven't got the cachet. Unfortunately I see the ones that came with the new tek scopes at work were switched ones, and most of the economy probes on the market are switched.

Look at your scope inputs and the capacitance load should be marked. Get 10:1 probes whose compensation range covers this value of capacitance. Otherwise you won't be able to get the pulse response up to spec.

David
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Old 15th Feb 2016, 11:42 pm   #3
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Default Re: Dodgy scope probes.

The probes pull apart just behind the switch. But they are really junky stuff and I dont use them anymore. They cost about $40 new here and I can mostly get some second hand Tek or HP or Gould for less than that. Unswitched of course.

Joe
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Old 15th Feb 2016, 11:59 pm   #4
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Default Re: Dodgy scope probes.

I have to say I've always had switched probes and not had any problems in daily commercial use. The biggest problems I've had is with yanked cable when someone else has kindly borrowed one.
I don't think for general audio or tv servicing use the inferior performance of a switched probe is a big deal. Mine is mostly on 10:1 but for testing domestic amplifiers for example or probing driver stages I flick it to 1:1.
I've only had 2 budget probes in 6 years and that's only because I trod on the first one. I bought them from Rapid.
If you tread on a probe or forget to disconnect it when you take a chassis off the bench and it goes 'ping', it's alot less stressful with a cheap probe. Expensive probes break just the same.
The main caveat would be direct imported chinese jobs where you can't always rely on the safety or insulation.

When I was a trainee working on RF in the low Ghz range we only had HP or Wandel & Goltermann which was a different story and they were so expensive it was all on contract rental!
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Old 16th Feb 2016, 7:53 am   #5
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Default Re: Dodgy scope probes.

Been using cheap probes off ebay for the last year or so with no problems, they're a bit beefier than your ones Graham- the grey ones. I paid a bit more than £5.99 though and from a UK ebayer. Not sure how good these are at RF, but they're fine for AF.

Andy.
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Old 16th Feb 2016, 10:41 am   #6
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Default Re: Dodgy scope probes.

I like the Coline M12 or M20 probes - blue bodies and replaceable cables. You can sometimes pick up NOS at a much better price than Tek or HP equivalents. Coline also rebranded them for the likes of RS at one time, so they sometimes appear under that guise. There is a thread on them on this forum, including some specifications. Try searching under 'Coline probe'

Mike

PS: Found the thread at https://www.vintage-radio.net/forum/...ad.php?t=90442. Reading it reminded me that Coline did do switched and unswitched versions. The specs for the unswitched versions are about two thirds down the thread (typically 250MHz for the x10 types). Coline also did cheaper black bodied probes but they are more like your dodgy type.

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Old 16th Feb 2016, 11:04 am   #7
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Default Re: Dodgy scope probes.

Dismantling that probe should be relatively straightforward once the front end has been unscrewed. The black plastic case should slide back along the cable revealing the assembly.

If you are unlucky the assembly may be in a soldered closed metal tube for screening with no access to the switch. If you do reach the switch it may be worth linking the switch contact out with say a resistor leg on the 10:1 setting so it is a permanent 10:1 probe.

I got a pair of new Agilent unswitched probes on Ebay last year for around £30.00 and they are very good. They also came with a bag of the usual things such as adaptors, spare tip and clip on coloured ident bands
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Old 16th Feb 2016, 11:08 am   #8
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Default Re: Dodgy scope probes.

The thing with probes (like many other things) is to keep your eyes open and grab good ones when they show up at good prices. If you set out to get something specific and at a time of your choosing, then it gets expensive.

David
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Old 16th Feb 2016, 2:19 pm   #9
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Default Re: Dodgy scope probes.

I've got 2 of those probes, and they are both knackered! I also have a nice one that came with my little Philips scope, but I bust the tip off... Really need to get some new ones!

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Old 16th Feb 2016, 4:11 pm   #10
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Default Re: Dodgy scope probes.

I got a couple of these from RS (x10), made in Germany, £11.67 + VAT free delivery.

http://uk.rs-online.com/web/p/oscill...robes/2089831/
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Old 16th Feb 2016, 11:32 pm   #11
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Default Re: Dodgy scope probes.

They look OK, will have to get some ordered!

Regards,
Lloyd.
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Old 17th Feb 2016, 3:36 pm   #12
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Default Re: Dodgy scope probes.

Thanks for all the replies.

I think I can safely say that these are cheap and nasty probes.

The pointed end unscrews and then the next section of black plastic can be slid off revealing the slide switch knob with a piece of sprung metal around it, supposedly to lock it either position. Unfortunately there's no access to the switch wiring which is enclosed in a tube. I wasn't able to slide off the last piece of plastic which surrounds the lead and I don't want to destroy the probe just yet.

I shall get some new unswitched probes, probably from RS Components.
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Old 17th Feb 2016, 4:07 pm   #13
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Default Re: Dodgy scope probes.

If you look at the flange just in front of the cable clamp it has 2 flats on it. These allow the works to be unscrewed and pulled free.

I have one of these probes that I was thinking of converting to a diode probe. If anyone is scrapping one can I buy the spring loaded tip and an earth lead.

Al
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Old 17th Feb 2016, 4:17 pm   #14
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Default Re: Dodgy scope probes.

Once I get new probes you're welcome to the parts you need.
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Old 17th Feb 2016, 4:26 pm   #15
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Default Re: Dodgy scope probes.

I have two good very probes, one x10 and another x100 (very useful on valve kit) they both 'fell off' the end of a design job. For day to day use I use very cheap ones, I think the last lot were a tenner for four, pretty terrible switched ones, I left them on x10 and heatshrunk some sleeving on them. Oddly not one has broken.
 
Old 17th Feb 2016, 7:16 pm   #16
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Default Re: Dodgy scope probes.

I had it drummed into me from early on, there are no short cuts with probes.
Those switchable ones are awful, I think I've got some somewhere. I know each Tek scope has a matching probe type, to attain the bandwidth.
A decent 10x probe or two should do for most things, one of my favourites are the HP 400701 (or something) very nice small probes. I've only got one though.

I'm with Radio Wrangler, keep your eyes open an grab them when you see them.
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Old 19th Feb 2016, 3:07 pm   #17
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Default Re: Dodgy scope probes.

Quote:
Originally Posted by Alistair D View Post
If you look at the flange just in front of the cable clamp it has 2 flats on it. These allow the works to be unscrewed and pulled free. Al
I can't get the piece of plastic surrounding the lead to slide off and I don't want to damage anything.

The switch doesn't seem to have any active contacts in the X10 position, so it's possible to lock it in position either with a small cable tie or heat shrink tubing as suggested earlier.
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Old 19th Feb 2016, 5:00 pm   #18
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Default Re: Dodgy scope probes.

On mine I managed to push the strain relief back by digging my nails into the seam that is just behind the switch. I will post a couple of pics tomorrow.

Al
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Old 20th Feb 2016, 2:20 pm   #19
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Default Re: Dodgy scope probes.

As promised,here are some pics of how to take the probe apart.

It does take a bit of effort to get the strain relief to start moving up the probe body.

As you can just about make out from the last picture the switch is a U shaped piece of metal pressing on gold plated tracks on the PCB. If you are lucky the tracks will not be worn away and just need a bit of cleaning.

I have just discovered that the lead on mine is intermittently open circuit at the probe end so thanks for the offer of parts but I will now just bin it.

Al
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Old 17th Mar 2016, 9:58 pm   #20
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Default Re: Dodgy scope probes.

Quote:
Originally Posted by martiR2R View Post
I got a couple of these from RS (x10), made in Germany, £11.67 + VAT free delivery.

http://uk.rs-online.com/web/p/oscill...robes/2089831/
I bought myself a pair of those probs. The X10 version. After a couple of weeks of use I'm well satisfied with them. Much better made than my cheapo ones and no more fiddling with the slide switch to get a reliable trace.

I'll see whether I can lock one of my cheapo ones in X1 mode and consign the other one to the WEEE Bin.

Thanks to all for the advice given.
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