Possible reasons *not* to get an analog oscilloscope

[watchmaker]

Agreed. Case in point; a few weeks ago a customer brought in a PC that was shutting down randomly. 12 V rail was within spec using a meter - but when viewed on the scope it had unbelievable magnitude switching transients on it. Scope for the win.

I think I had a similar situation with a PSU that tried to fry my fiber laser. It looked normal on a DMM, but managed to fry a 10A relay. Rather than connecting my scope to see what it looked like, I replaced everything. I wasn't certain my probe would have been good enough to protect my scope.

Are you going to make your program available?  (For fee or not).

THANKS


Speaking of power supplies, this came through the door this afternoon. One of these rails is not like the others ...

... I don't think the bench multimeter would have flagged it as anything abnormal.

I had one a few months ago that tripped a 40 amp breaker and fused the contacts on a switch. Didn't do a lot for my nerves or ears at the moment I turned it on either. I started using a dim bulb tester for suspicious PSUs after that - and it's already caught one that was about to do the same thing.

[Aldo22]

... I don't think the bench multimeter would have flagged it as anything abnormal.

It depends.
If the DMM has a DC & AC mode, you can definitely see that there's an AC component.
At least enough that you'll want to check with an oscilloscope later to see exactly what it is. 
Of course, you can also test for AC using a DMM without DC&AC, but you have to think of it first, and it doesn't occur to you right away.

[CJSouthern]

Are you going to make your program available?  (For fee or not).

THANKS

To be honest, nobody really seems particularly interested in it so in retrospect, I think I might just keep developing it for myself and see where it ends up.

Currently, it's a "full toolbox" consisting of tools that vary in use from "all the time" (eg a screenshot on the clipboard by holding both mouse buttons down for a second or two) to stuff most people probably wouldn't use. Some of it is a "shite-load" easier than trying to do it via the scope's interface (eg saving setups direct to PC - anywhere you like).

It's also, currently, undergoing several dozen builds a day as I tweak things, zap a few bugs, add new stuff, and generally refine things - so any build is quickly out of date.

Having said all that - if you'd like a copy - then pop me a PM. The pre-requisites are a 1920 x 1080 monitor - Windows - and a mouse with a couple of buttons and a scroll wheel.

[CJSouthern]

... I don't think the bench multimeter would have flagged it as anything abnormal.

It depends.
If the DMM has a DC & AC mode, you can definitely see that there's an AC component.
At least enough that you'll want to check with an oscilloscope later to see exactly what it is. 
Of course, you can also test for AC using a DMM without DC&AC, but you have to think of it first, and it doesn't occur to you right away.

Thanks. My daily driver bench meter is a Siglent 4065A; I could probably configure it to pick it up - but it almost becomes a catch 22 of not knowing what to configure it to unless you know what the anomaly is (or knowledge of it even being there are all) - so in the end, a "visual explorer" like a scope is far more the right tool for the job (for me) than the DMM as I really don't need 6 1/2 digit resolution of a PSU rail - but I do need the easiest possible visualisation of what's happening.

Probably a good case-in-point was one the other day with 200mV+ of switching transients on the 12V rail at a few hundred kilohertz; child's play for the scope.

[KungFuJosh]

Actually, that's exactly where I'd use my old HP 180A over my fancy Siglent DSO   

That old gear can often take a lot more abuse than modern stuff.

If you have room for a boat anchor, by all means.

Actually, I'd consider getting an SDS800X HD for the same purpose.

There's no way I'd want to risk my Magnova for a $67 PSU...especially not when it only takes a day for a new one to arrive.

[Aldo22]

Thanks. My daily driver bench meter is a Siglent 4065A; I could probably configure it to pick it up - but it almost becomes a catch 22 of not knowing what to configure it to unless you know what the anomaly is (or knowledge of it even being there are all) - so in the end, a "visual explorer" like a scope is far more the right tool for the job (for me) than the DMM as I really don't need 6 1/2 digit resolution of a PSU rail - but I do need the easiest possible visualisation of what's happening.

Well, but if you just want to measure DC, you wouldn't use an oscilloscope for that.

DC&AC mode is exactly for situations where you don't expect an AC component, but it shows up anyway.
Then you can use the scope to see what's going on.
I don’t have a Siglent 4065A, but on the ZT-225, it’s just one setting on the switch.
You don’t have to configure anything.

[TomKatt]

Actually, that's exactly where I'd use my old HP 180A over my fancy Siglent DSO   

That old gear can often take a lot more abuse than modern stuff.

If you have room for a boat anchor, by all means.

Actually, I'd consider getting an SDS800X HD for the same purpose.

There's no way I'd want to risk my Magnova for a $67 PSU...especially not when it only takes a day for a new one to arrive.

Touche' 

My Siglent isn't so fancy in comparison lol.  But it is the fanciest piece of kit on my bench. And the HP180A boat anchor isn't really 'huge', but it certainly does take some effort to move around (it's got a high specific gravity lol).

[KungFuJosh]

(it's got a high specific gravity lol).

Sounds like a boat anchor. 

[zike]

My Siglent isn't so fancy in comparison lol.  But it is the fanciest piece of kit on my bench. And the HP180A boat anchor isn't really 'huge', but it certainly does take some effort to move around (it's got a high specific gravity lol).

Try a Tek 310A (all tube, but small). I know a cat that uses his to tune Tesla coils.

[tautech]

Thanks. My daily driver bench meter is a Siglent 4065A; I could probably configure it to pick it up - but it almost becomes a catch 22 of not knowing what to configure it to unless you know what the anomaly is (or knowledge of it even being there are all) - so in the end, a "visual explorer" like a scope is far more the right tool for the job (for me) than the DMM as I really don't need 6 1/2 digit resolution of a PSU rail - but I do need the easiest possible visualisation of what's happening.

Well, but if you just want to measure DC, you wouldn't use an oscilloscope for that.

DC&AC mode is exactly for situations where you don't expect an AC component, but it shows up anyway.
Then you can use the scope to see what's going on.
I don’t have a Siglent 4065A, but on the ZT-225, it’s just one setting on the switch.
You don’t have to configure anything.

Why not when precise accuracy isn't required ?

The first requirement of fault finding is to check all power rails are present and near their stated values.
Then while one is at it one can immediately see if ripple is present.

Sure the better DMM's offer DC+AC measurements but if you don't have one a scope is quite adequate for initial tests.
The modern DSO is quite capable of resolving a 4.8-5.2V spec for a 5V rail.

[CJSouthern]

Thanks. My daily driver bench meter is a Siglent 4065A; I could probably configure it to pick it up - but it almost becomes a catch 22 of not knowing what to configure it to unless you know what the anomaly is (or knowledge of it even being there are all) - so in the end, a "visual explorer" like a scope is far more the right tool for the job (for me) than the DMM as I really don't need 6 1/2 digit resolution of a PSU rail - but I do need the easiest possible visualisation of what's happening.

Well, but if you just want to measure DC, you wouldn't use an oscilloscope for that.

Actually, I often DO use an oscilloscope for exactly that; with an RMS measurement added to a channel it gives me a DC reading just fine.

Case-in-point - laptops; if one is brought in for repair, and I want to quickly check all the various VRMs/rails, I get by far the best overview from the scope.

In contrast, if I'm trying to track down a short on a rail or set up a precise reference voltage (without unduly biasing the reading by loading it) then DMM all day long.

Horses, courses etc; obviously a significant overlap between the two - and nothing is "set in concrete". I usually just run with whatever gives me what I need to know first time round; for PSUs, that's usually a scope.

[2N3055]

Thanks. My daily driver bench meter is a Siglent 4065A; I could probably configure it to pick it up - but it almost becomes a catch 22 of not knowing what to configure it to unless you know what the anomaly is (or knowledge of it even being there are all) - so in the end, a "visual explorer" like a scope is far more the right tool for the job (for me) than the DMM as I really don't need 6 1/2 digit resolution of a PSU rail - but I do need the easiest possible visualisation of what's happening.

Well, but if you just want to measure DC, you wouldn't use an oscilloscope for that.

DC&AC mode is exactly for situations where you don't expect an AC component, but it shows up anyway.
Then you can use the scope to see what's going on.
I don’t have a Siglent 4065A, but on the ZT-225, it’s just one setting on the switch.
You don’t have to configure anything.

Like I said, you can do that only if you are measuring a battery, outside device. Otherwise, you don't know if there is only DC there.
Funny enough you can have ripple on the battery too, if connected and you are loading it with pulse load/switcher or charging with switcher or some kind of pulse charger (they exist). Extensive ripple in that case would point to large internal resistance of the battery, which could point to bad/ decreased capacity/empty battery.

Best is to go the other way around. You probe everything with scope (provide you are working on low voltage device that doesn't hide 5000V in weird places) and that is usually good enough for go/no-go test. I used 3.5 digit meter many times to check status of SLA batteries and if they charge. If you want to balance Li-ion cells in a pack to millivolts, then break out decent multimeter for additional decimal places.
Although SDS800xHD will do that well enough too, because it will still show millivolts on 3,7V cell, and since you are balancing (comparing) cells, that is relative measurement that is not dependent on DC absolute accuracy specification  0.5%.

Multimeter is on my desk all the time because of other stuff, diodes, continuity, etc. mostly. Voltage measurement with multimeter comes when we already know what are we measuring and want more detail or accuracy.

For instance, I just repaired old external rack mount Soundcraft PSU for a big sound console. It has several voltage buses. All of them checked by scope first, found problem with the scope, used meter to check connections, tweezers for resistance of some suspicious resistors, and checked few diodes. Then repaired it and finally checked ripple with scope and used multimeter to set exact voltages.
That final step was not needed whatsoever, that was simply my OCD of "doing things right".
So apart from last step (that was not needed, scope voltage measurement would have been better than PSU spec) I used scope and resistance, continuity and diode test on meter and tweezer.

As for measuring ripple with meter, unless you are measuring 50 Hz ripple, you will not see much on simple multimeters. And even then, limited bandwidth might cause lots of error. Scope is exactly the tool for that. From 50 Hz to multi MHz switchers ripple.
With signal shape on the screen, 6 measurements at the same time, histograms and FFT.  It is really fast and gives so much information at the same time. You touch the probe to test point and you go "Aha!" and move on until you get to problem.

And it is universal principle both for devices you know well (where you exactly know what you expect to see on what point) and for something you never saw before, where you need to reverse engineer how it works.

[CJSouthern]

Thanks. My daily driver bench meter is a Siglent 4065A; I could probably configure it to pick it up - but it almost becomes a catch 22 of not knowing what to configure it to unless you know what the anomaly is (or knowledge of it even being there are all) - so in the end, a "visual explorer" like a scope is far more the right tool for the job (for me) than the DMM as I really don't need 6 1/2 digit resolution of a PSU rail - but I do need the easiest possible visualisation of what's happening.

Well, but if you just want to measure DC, you wouldn't use an oscilloscope for that.

DC&AC mode is exactly for situations where you don't expect an AC component, but it shows up anyway.
Then you can use the scope to see what's going on.
I don’t have a Siglent 4065A, but on the ZT-225, it’s just one setting on the switch.
You don’t have to configure anything.

Funny enough you can have ripple on the battery too

True story: Back in the 80's I worked as a senior avionics tech at the Electronic Equipment Calibration Centre in the RNZAF. We had an antenna / probe that could be attached to our 22 GHz HP spectrum analyser which - naturally - we sometimes used to demodulate AM radio stations (as you do).

One day we spotted a new relatively strong spike of several GHz. Intrigued, we put the spectrum analyser on an extention cord and wheeled the trolley around the various bays to find the source of the signal (conjecturing about spy agencies and bugs as we did so).

To cut a long story short, we eventually traced it to a cell in a rechargable battery in a bit of test equipment. Weirdest thing I saw in my life; just one of those "quirks of nature" I guess.

[mawyatt]

One day we spotted a new relatively strong spike of several GHz. Intrigued, we put the spectrum analyser on an extention cord and wheeled the trolley around the various bays to find the source of the signal (conjecturing about spy agencies and bugs as we did so).

To cut a long story short, we eventually traced it to a cell in a rechargable battery in a bit of test equipment. Weirdest thing I saw in my life; just one of those "quirks of nature" I guess.

Just maybe that "Rechargeable Battery" was more than just a Battery

Best

[CJSouthern]

One day we spotted a new relatively strong spike of several GHz. Intrigued, we put the spectrum analyser on an extention cord and wheeled the trolley around the various bays to find the source of the signal (conjecturing about spy agencies and bugs as we did so).

To cut a long story short, we eventually traced it to a cell in a rechargable battery in a bit of test equipment. Weirdest thing I saw in my life; just one of those "quirks of nature" I guess.

Just maybe that "Rechargeable Battery" was more than just a Battery

Best

That was certainly the (light-hearted) speculation at the time - but I'm not aware that the port-mortum revealed anything sinister.

[KungFuJosh]

Maybe all the leaky Duracell batteries are really spy microphones melting to get rid of the evidence. 🤔

[CJSouthern]

Maybe all the leaky Duracell batteries are really spy microphones melting to get rid of the evidence. 🤔

Who knows; pretty sure these would have been Ni-Cd.

If there's one thing I hate about Alkaline batteries ...

[Uup]

Maybe all the leaky Duracell batteries are really spy microphones melting to get rid of the evidence. 🤔

Who knows; pretty sure these would have been Ni-Cd.

If there's one thing I hate about Alkaline batteries ...

Perhaps the test equipment was incidentally driving a radio emission out of the battery, the battery acting as an antenna of sorts.

In a similar, albeit in reverse, situation we had an issue with our apparently well shielded German made device that was a component for a laser guidance system for BAE Systems in Newcastle (early 2000s). Turned out the issue was caused by the emissions from a prototype tracking system in the adjacent lab. A backup battery in our device was acting like an antenna and happened to be at the resonant frequency of the scattered emissions from tracking system. It was embarrassing, however, I got to enjoy a front row viewing watching an evaluation of six F/A-18s laden with new weapons systems doing 'touch and goes' - in formation, landing then taking off, one after the other in multiple loop cycles.

[CJSouthern]

Maybe all the leaky Duracell batteries are really spy microphones melting to get rid of the evidence. 🤔

Who knows; pretty sure these would have been Ni-Cd.

If there's one thing I hate about Alkaline batteries ...

Perhaps the test equipment was incidentally driving a radio emission out of the battery, the battery acting as an antenna of sorts.

In a similar, albeit in reverse, situation we had an issue with our apparently well shielded German made device that was a component for a laser guidance system for BAE Systems in Newcastle (early 2000s). Turned out the issue was caused by the emissions from a prototype tracking system in the adjacent lab. A backup battery in our device was acting like an antenna and happened to be at the resonant frequency of the scattered emissions from tracking system. It was embarrassing, however, I got to enjoy a front row viewing watching an evaluation of six F/A-18s laden with new weapons systems doing 'touch and goes' - in formation, landing then taking off, one after the other in multiple loop cycles.

To be honest, it was some 45 years ago ... so some of the details are a bit hazy now. Off memory the device was some kind of HP signal generator; it was normally mains supplied, but had a small battery to extend it's use into the field a bit. Off memory the battery only lasted about 90 minutes on a good day.

The unit was on the shelf with other test equipment & powered off - which in those days probably meant a mechanical power switch - so I doubt the battery would have been powering any of the internals - and they weren't getting power from the mains.

I'm a big F-18 fan; I was quite active in aviation in a "previous life" albeit only at a GA level, but as they say "you can take the pilot out of an airplane, but you can never take the airplane out of the pilot". We had the A4K Skyhawks when I was in the RNZAF - would have been great if they'd bought F-18s. I do have it's flight manual and a model that sits on the back of my couch. But I digress!

[Uup]

I'm a big F-18 fan; I was quite active in aviation in a "previous life" albeit only at a GA level, but as they say "you can take the pilot out of an airplane, but you can never take the airplane out of the pilot". We had the A4K Skyhawks when I was in the RNZAF - would have been great if they'd bought F-18s. I do have it's flight manual and a model that sits on the back of my couch. But I digress!

I think I can understand why. Prior to that experience, I had only seen them in movies. In person, hearing and feeling them land then go full throttle and take back off, one after the other... that was genuinely exciting, and I was already excited when I was shown around the labs at BAE Systems. It certainly piqued my interest in aviation. I would love to own a plane, although, I think it would be somewhat worse than owning a reasonable size boat, a money pit for sure.

[Aldo22]

@tautech
@CJSouthern
@2N3055

Of course, the scope is superior when it comes to measuring and visualizing AC. That’s absolutely clear.
But often, for the sake of convenience, you’ll start with a handheld DMM, and then a DMM with AC&DC display might alert you that you should take a closer look at the AC component with a scope.
It’s not even a question of whether the DMM’s AC RMS measurement is accurate in this case—any value >0 indicates that you should take a closer look.
It’s not perfect, just a small advantage.
For me, this dual display has been helpful on several occasions.

By the way, I write AC&DC instead of AC+DC because I’m referring to the dual display.
AC+DC is the value that corresponds to the RMS measurement of an oscilloscope in DC coupling.

[CJSouthern]

But often, for the sake of convenience, you’ll start with a handheld DMM, and then a DMM with AC&DC display might alert you that you should take a closer look at the AC component with a scope.

Um no - not really. Not for me anyway.

DUTs are examined on my bench where I have the scope sitting about 45 degrees @ 40 cm to my right, and the DMM sitting at about 45 degrees @ 40 cm to my left. There's nothing "more convenient" about starting with any DMM with my workflow.

When the DMM may - or may not - do the job ... but the scope can unequivocally to the job - with less chance of missing something - it just doesn't make sense to me to start with a tool that either (a) may miss a clue or (b) is going to need the better tool even if it does find a clue then I may just as well start with the more capable tool to start with; it's not like I'm paying for more expensive tokens to use the scope.

[2N3055]

@tautech
@CJSouthern
@2N3055

Of course, the scope is superior when it comes to measuring and visualizing AC. That’s absolutely clear.
But often, for the sake of convenience, you’ll start with a handheld DMM, and then a DMM with AC&DC display might alert you that you should take a closer look at the AC component with a scope.
It’s not even a question of whether the DMM’s AC RMS measurement is accurate in this case—any value >0 indicates that you should take a closer look.
It’s not perfect, just a small advantage.
For me, this dual display has been helpful on several occasions.

By the way, I write AC&DC instead of AC+DC because I’m referring to the dual display.
AC+DC is the value that corresponds to the RMS measurement of an oscilloscope in DC coupling.

You missed the point. You can accomplish the goal both ways. One is more thorough, efficient and faster.

It is exactly for the sake of convenience more efficient and faster to start with the scope.
As far as the voltage measurement goes it gives you immediately so much more information.  No need to measure a point twice or trice with 3 different instruments just to be sure. Why rely on meter to "maybe give you a hint to check with the scope" when you have the real thing available right there.

That is provided you have scope available. That is why portable scope is a thing, because sometimes you are not in the lab. And that is actual use case of those handheld scopes, even the very cheap ones. It beats multimeter by a mile, even a crappy little scope.

Look, you got very similar advice from several people that are doing this on daily basis for years. We feed the family with this work.
It is not just rhetoric, it workflow devised from practice to do good job fast, issue an invoice and go home.
It was free advice and given in good faith.
Use it or not, it is your life. You decide.

[Aldo22]

I'm not arguing for my position here, because I don't have one. 
It was just meant to be a suggestion.
A lot depends on what equipment you have available.
If you only have a desktop scope and a handheld DMM and don't want to lug the DUT to the scope or vice versa beforehand, then it can be an advantage.
It depends on the situation. It's not that important, and it's certainly not a matter of "my life". 

[Sorama]

@tautech
@CJSouthern
@2N3055

Of course, the scope is superior when it comes to measuring and visualizing AC. That’s absolutely clear.
But often, for the sake of convenience, you’ll start with a handheld DMM, and then a DMM with AC&DC display might alert you that you should take a closer look at the AC component with a scope.
It’s not even a question of whether the DMM’s AC RMS measurement is accurate in this case—any value >0 indicates that you should take a closer look.
It’s not perfect, just a small advantage.
For me, this dual display has been helpful on several occasions.

By the way, I write AC&DC instead of AC+DC because I’m referring to the dual display.
AC+DC is the value that corresponds to the RMS measurement of an oscilloscope in DC coupling.

You missed the point. You can accomplish the goal both ways. One is more thorough, efficient and faster.

It is exactly for the sake of convenience more efficient and faster to start with the scope.
As far as the voltage measurement goes it gives you immediately so much more information.  No need to measure a point twice or trice with 3 different instruments just to be sure. Why rely on meter to "maybe give you a hint to check with the scope" when you have the real thing available right there.

That is provided you have scope available. That is why portable scope is a thing, because sometimes you are not in the lab. And that is actual use case of those handheld scopes, even the very cheap ones. It beats multimeter by a mile, even a crappy little scope.

Look, you got very similar advice from several people that are doing this on daily basis for years. We feed the family with this work.
It is not just rhetoric, it workflow devised from practice to do good job fast, issue an invoice and go home.
It was free advice and given in good faith.
Use it or not, it is your life. You decide.

I completely agree with 2N3055.

A scope should be your first tool to analyse an issue.