Request: how to not blow up oscilloscope

PTL-Pioneer

Super Member
Hi all, how does one tell, how not to blow up oscilloscope?
Been reading up on the topic, is it simply if the unit is not connected to mains earth, you can connect the oscilloscope clip to chassis while probing?

I mean if i pull the schematic for a receiver - and there is grounding to the receiver chassis, does that mean i can safely connect probe earth to chassis, without causing any damage to myself, equipment and scope?

Or is there many more nuances involved
 
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There are a few ways to get into trouble with a scope. One is to send in too much voltage using a 1:1 probe to the channel inputs. Look at the scope face, there should be a MAX voltage spec. written there. Don't ever exceed that voltage.
Second, even if you cross up the grounding badly, the negative wire on the probe will burn out but not the scope. Also, watch out for bridged amplifiers. You CAN NOT connect the two (black) common terminals together with two probes, you'll get a big spark and damage the amp. I know because I've blown a couple of amps in my time this way. I read them one channel at a time. If in doubt, I will flick the ground wire from the probe on the chassis really fast to see if there is a spark.
 
I have had a scope for a few years and not ever hooked it up because I have yet to find an instruction clear enough to be secure to do so. Those in the know take way too much for granted and assume we have knowledge when the whole point is that we don't. We need to be taken by the hand and shown, not be impressed by someone's expertise.
 
Wow thank you all, i have seen the videos and to me it looks like as long as the circuit under test is not connected to mains earth, i should be fine. So i def said to myself - Cant be that simple.
That why i was kind of freaking out - its one thing working on a unit powered off and caps discharged safely to "Pricking around" with voltages than can kill me, not to mention blow up the gear i can barley afford to buy.
 
I have had a scope for a few years and not ever hooked it up because I have yet to find an instruction clear enough to be secure to do so. Those in the know take way too much for granted and assume we have knowledge when the whole point is that we don't. We need to be taken by the hand and shown, not be impressed by someone's expertise.
The problem is that when someone writes "I want to use an oscilloscope", those of us with some electronics knowledge generally assume the writer has followed a similar path that we have: We learned some electrics and electronics, and then we learned to use an oscilloscope.

But it turns out that when some folks write, "I want to use an oscilloscope", they have no electrical or electronics experience. Unfortunately, then even the best-intentioned, simplest oscilloscope tutorials -- which all assume some knowledge of electrics and electronics -- only lead to confusion, frustration, and occasionally a damaged oscilloscope and even more rarely, a damaged human.

Not to mention the fact that without knowing some electrics and electronics, the oscilloscope display will be almost completely meaningless...

Simply put, an oscilloscope is not a good place to start learning electronics. A good place to start is the US Navy NEETS modules, http://electriciantraining.tpub.com/, starting at Module 1.

You'll get to oscilloscopes at Module 16 of 24.
 
The problem is that when someone writes "I want to use an oscilloscope", those of us with some electronics knowledge generally assume the writer has followed a similar path that we have: We learned some electrics and electronics, and then we learned to use an oscilloscope.

But it turns out that when some folks write, "I want to use an oscilloscope", they have no electrical or electronics experience. Unfortunately, then even the best-intentioned, simplest oscilloscope tutorials -- which all assume some knowledge of electrics and electronics -- only lead to confusion, frustration, and occasionally a damaged oscilloscope and even more rarely, a damaged human.

Not to mention the fact that without knowing some electrics and electronics, the oscilloscope display will be almost completely meaningless...

Simply put, an oscilloscope is not a good place to start learning electronics. A good place to start is the US Navy NEETS modules, http://electriciantraining.tpub.com/, starting at Module 1.

You'll get to oscilloscopes at Module 16 of 24.
excellent post; good point(s).
(and, FWIW, I'll second the NEETS course modules; the older the better, IMO, to actually learn from -- but I'm a bit of a Luddite)
 
...As usual Dave, you've yet to actually read what's written in a post. You love to jump on every opportunity to dress it down...

That's unfair. Dave clearly read the post and posted what appears to be a reasoned and sensible reply along with a good suggestion on learning.

An oscilloscope is a sophisticated measurement device. It needs a comprehensive understanding of how to interpret what it displays. That cannot be gained without putting the time in to learn the basics first. There is no short-cut, back-of-the-cereal-box, crash course.

No different to buying an ECG monitor with no medical training whatsoever. Look at this in an ECG basics diagram:

ecg.png

I look at oscilloscopes all day and yet this display of a heartbeat means nothing to me. My retired doctor father or mother (nurse) could tell me what it all means, but I can't learn how to interpret minor differences in order to pinpoint issues without learning the basics.
 
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You do not want to answer a novice saying "yes, no problem" and they find him electrocuted on the floor having the AK web page still open. :confused:

Now the "nuances"usually are "it depends" , "YMMV", etc.

Wow thank you all, i have seen the videos and to me it looks like as long as the circuit under test is not connected to mains earth, i should be fine. So i def said to myself - Cant be that simple.
That why i was kind of freaking out - its one thing working on a unit powered off and caps discharged safely to "Pricking around" with voltages than can kill me, not to mention blow up the gear i can barley afford to buy.
Yes, of course this applies if there are no mains shorts to the chassis.
Some vintage stuff is not that well insulated.
Here the death cap of a Harman Kardon Citation, which was mounted by some idiot (have three HK Citation all built while quality control asleep). If the paint on the cap is thin or compromised it can put the whole thing on mains voltage.
That is why many techs may ground the chassis as well as the oscilloscope, depending on the situation.

So again: it depends..

http://members.quicknet.nl/gerard.slikker/hk-citation-fourteen-cer.jpg
 
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Okay, the troll shall not respond any longer to this thread.

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indeed. Additionally, OP and others may not be aware a lot of us techs (at least me, myself, I and some others at work) have had actual experiences which could have lead the picture posted by @restorer-john being a flat line...;)
 
...So the response should always be "no, I'm not going to risk someone electrocuting themselves"...

Basically, yes.

When people roll into AK as new members asking about 'repairing' their gear, you'll note that the defacto resident experts will ask a common set of questions to determine the skill-set and knowledge level people have. Quite often it is clear those people shouldn't be even considering taking the cover off something, let-alone wielding a soldering iron.

Nobody wants an electrocution, and when people are soliciting advice, across the internet, about specific technical procedures which often require two hands to be placed into mains attached, live gear, everyone has to always err on the side of caution.

Oscilloscopes are awesome pieces of gear and DSOs are so cheap now, it is crazy. I couldn't have dreamed of the functionality you can get in a $400 DSO these days, back when, as a 22yo I saved up $750 to buy a 20MHz dual trace CRO. Start with battery powered amplification and electronics with your 'scope and don't move to mains powered anything until you can operate it with your eyes closed.
 
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...and others may not be aware a lot of us techs (at least me, myself, I and some others at work) have had actual experiences which could have lead the picture posted by @restorer-john being a flat line...

The truth is 3 times in 40 years for me. Each was just a split second shock, but enough to know what 240v (678V peak to peak) feels like. The last one could have killed me and it was due to house wiring practices which make no sense to an electronics technician.

Each one was quite different, but each involved assumptions on my part and with hindsight, each was totally preventable.
 
All good advice, thank you, I feel stupid when dealing with this stuff, I really am trying to learn as I go, (i am going through all the documents kindly provided) its just I simply find electronics hard to truly understand. It takes lots of time, a rare commodity in my life.
Videos galore and websites galore, lots of information, digestion of which and conflicts between, tend to make it that bit more difficult. AK is where I go for everything.
 
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Start with a cheap scope, and a low voltage device. Play with it, adjust it, get in touch with your inner kid.
Some serious tips:
Get 10x probes. They attenuate the measured voltage, allowing you to measure 10x the peak voltage that a 1:1 probe would.
Get extras. You will probably bend, break or otherwise destroy several probes. What you read about scopes will make more sense after you have played with one.
 
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