New Oscilloscope - where do I start?

James Knox

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Just bought new Rigol Scope that should arrive the end of the week.

I don’t know why I put it off for so long - I’ve spend more money on Overdrive and Delay Pedals, lol.

I’ve been experimenting with some point to point builds and running into some troubleshooting which appears to be oscillation problems. I learned that with an Oscilloscope, you get to “see” things you often can not hear.

I watched an Uncle Doug @D-Labs Video where he went through the circuit of a Silverface Champ pointing out how the scope allows one to “see” the signal getting amplified.

Seems like a very useful troubleshooting tool. I’m excited to find “unwanted noise” with my new tool. Having never used a scope before, and knowing that it is “different” than my DMM.....

Where do I start? Any Beginner Tutorials/Resources you might recommend?
 

scooteraz

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Just bought new Rigol Scope that should arrive the end of the week.

I don’t know why I put it off for so long - I’ve spend more money on Overdrive and Delay Pedals, lol.

I’ve been experimenting with some point to point builds and running into some troubleshooting which appears to be oscillation problems. I learned that with an Oscilloscope, you get to “see” things you often can not hear.

I watched an Uncle Doug @D-Labs Video where he went through the circuit of a Silverface Champ pointing out how the scope allows one to “see” the signal getting amplified.

Seems like a very useful troubleshooting tool. I’m excited to find “unwanted noise” with my new tool. Having never used a scope before, and knowing that it is “different” than my DMM.....

Where do I start? Any Beginner Tutorials/Resources you might recommend?


Go to YouTube. Type in “Rigol Oscilloscope Tutorial”. You will have lots of choices. There were too many for me to link here.

I realize it can be a bit daunting, but one of those should suit.
 

bebopbrain

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Congrats. You will wonder how you went so long without the ability to see electrical signals.

The number one thing to be aware of is that the negative terminal of the scope probe in most cases is hard tied to earth ground. If you connect it to something that is floating, it won't be floating any more.

Make sure you understand the AC and DC voltage limits for your probes and scope.

It is helpful to distinguish between auto mode where the signal is always shooting across the screen and normal mode where the signal only goes across the screen when it gets a trigger. Often start in auto to find the signal and then switch to normal to only see the interesting stuff.
 

AlfaNovember

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I'm not familiar with the functions of that particular scope, but: You will probably want something to serve as a "function generator" - something to inject a known signal - often a sine wave, sometimes a square wave or sawtooth - into the circuit.

In the olde days, it was another piece of test equipment on the bench. Now I suppose there are modern options for short money from overseas vendors, or you can fashion your own by recording a selection of audio tracks onto a ipod or something.

In any case - Much of the work with a scope is done by looking carefully at how the signal deviates from the known shape of a sinewave, or in many cases, manipulating the scale and position of the two channels to overlap one another. Just playing a note on a guitar will look mostly like a scribble; for real insight you need something with a smooth waveform.

As for learning how to use it - Look for '50s era instructional resources like the old US Navy Electricity and Electronics Training docs (NEETS) which will cover the basics without all the modern digital-logic stuff. If you need a refresher on tube amp topologies, the '40s vintage RCA Receiving Tube Manuals are excellent resources which cover most topics found inside of most tube guitar amps.

Edit: This looks promising:

https://archive.org/details/HowToServiceRadiosWithAnOscilloscope/page/n49/
 
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wabashslim

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My first scope was in 1965, an EICO kit. I remember how happy I was to finally get a used Tek that had triggered sweep.
I learned on Eico scopes in 60's high school. Then I didn't touch another one till I got my first electronics job 10 years later. That "new" triggered sweep really threw me...once I realized how it worked - greatest thing since hole-free white bread!
 

SRHmusic

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Congrats. You will wonder how you went so long without the ability to see electrical signals.

The number one thing to be aware of is that the negative terminal of the scope probe in most cases is hard tied to earth ground. If you connect it to something that is floating, it won't be floating any more.

Make sure you understand the AC and DC voltage limits for your probes and scope.

It is helpful to distinguish between auto mode where the signal is always shooting across the screen and normal mode where the signal only goes across the screen when it gets a trigger. Often start in auto to find the signal and then switch to normal to only see the interesting stuff.
Good post.

@James Knox Note, 'normal' mode is the 'triggered' sweep mode, where the display is updated starting at a point where the signal crosses the trigger threshold. So learn how to set the trigger threshold and position or time offset, and you'll be able to get a nice stable trace image.

As @AlfaNovember notes, a function generator or audio sig. gen. is important to have so you have a constant (er, persistent) signal running into the circuit. Just a sine wave generator may be fine for amps. There are probably some project pages online on building one for yourself!

Yes, once I forgot that the probe I was using wasn't a differential or floating probe, and I blew an unprotected output stage when probing in an amp that was apparently too cheap to bother with an overcurrent protect circuit. :rolleyes:
 

kbold

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The number one thing to be aware of is that the negative terminal of the scope probe in most cases is hard tied to earth ground. If you connect it to something that is floating, it won't be floating any more.

^^ No. 1 important thing to remember.
Also, in most cases, all grounds are commoned (all at earth potential), so best to remove all ground clips (except for one) from probes. That one clip you connect to the chassis/0V.

Very few CRO's have clips floating or isolated from each other.
You can set up 2 inputs to work as a floating/differential input: Remove both ground clips set up measurement as A-B. Now one probe is a floating reference and the other the input. This is the best way to measure across a component in a circuit. (You just don't know what your 'reference' voltage/signal is.)

2) Read the manual (twice)
3) Practice on your pedals first, to get used to using a CRO.

Be very careful when testing valve amps: the voltages, besides potentially being able to kill, may be above the voltage capacity of the CRO or the probes.

 

Mowgli

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For newbies I strongly recommend two Youtube guys and a book section:

Mark at "Blueglow Electronics." His safety, isolation transformer and oscilloscope introduction videos are outstanding. (Uncle Doug's video on isolation transformers is outstanding, too.).

Alan at "w2aew" is a Textronix design engineer and an absolutely incredible resource and teacher. His introduction to oscilloscope videos are great, too.

There's a book I discovered at my public library years ago: How to diagnose and fix everything electronic by Michael Jay Grier. It's section on oscilloscope use is outstanding.

Hope this helps.
 

James Knox

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For newbies I strongly recommend two Youtube guys and a book section:

Mark at "Blueglow Electronics." His safety, isolation transformer and oscilloscope introduction videos are outstanding. (Uncle Doug's video on isolation transformers is outstanding, too.).

Alan at "w2aew" is a Textronix design engineer and an absolutely incredible resource and teacher. His introduction to oscilloscope videos are great, too.

There's a book I discovered at my public library years ago: How to diagnose and fix everything electronic by Michael Jay Grier. It's section on oscilloscope use is outstanding.

Hope this helps.

Thank you - I will look into those!
 

dsutton24

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Start off easy, and for heaven's sake, don't do near any tube gear until you understand the thing. Getting a ground attached to something where it shouldn't be, or fumbling a polarity switch can cause damage.

Find yourself a 70s or 80s vintage table radio or stereo gear, and find an approximate schematic. Trace your way through that thing, learn on something sacrificial and low voltage.
 

Mowgli

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Let me 2nd the advice of dsutton and others - tube gear is usually high voltage and can hurt/kill you if you aren't careful.

And even when you are careful, a hand can slip and damage either you or a piece of equipment.

I accidentally slipped with a DMM probe once and shorted a circuit in a device. I was demoralized because I was about 2 steps from finishing the repair on it. The short caused damage to the radio and I had to spend additional time diagnosing the damage I caused! Thankfully I wasn't shocked.

I and others will recommend that you get a true "isolation transformer" (not just a variac - most of those don't truly isolate the house voltage from the "device under test"- DUT - voltage). After you acquire one, you may wish to also employ a variac and a current limiter (high voltage light bulb in series with hot feed) in tandem with your Isotran. Then you can plug your DUTs (e.g. amps, radios, toasters, fans, etc.) into your isolation transformer/variac/current limiter chain while keeping your oscilloscope grounded to earth ground (standard 3-prong plug into a wall socket and/or power strip with surge protection). This way your scope will have a proper reference voltage and you can control the applied voltage to the DUT while checking for shorts with the current limiter! If this is confusing to you, you need to do some reading and viewing of videos.

So start with low voltage and small current DUTs if you are just learning and make sure you gain great familiarity with your DMM/VOM, too - the DMM/VOM will be more useful than the scope in most situations.

Make sure your DMM/VOM has a high input impedance. Otherwise, it may shunt current away from the DUT and through the meter. This will give you inaccurate readings. 10 megaohms is a reasonable minimum input impedance for a DMM/VOM/old school VacuumTubeVOM.

Lastly, Mark at Blueglow correctly states that you can usually avoid probing the really high voltages (e.g. plate voltages, B+/power supply voltages) by just using the scope at low voltage sites in circuits (like the tube input grids) where you can evaluate the signals and how they are behaving. You can usually avoid the high voltage plates with the scope - many of those are usually best assessed with the DMM/VOM!

So learn WHERE to probe with the scope probes and WHERE to measure with your DMM/VOM probes before just touching the scope probe tip where it may be interesting. Sometimes when you want to see the "ripple" voltage coming from the power supply you will have to put the scope probe on a high voltage node. So learning to do so safely is imperative. Such knowledge can save both your body and your test equipment.

Good Luck and feel free to ask questions after reading and viewing the videos. Better to eliminate ignorance than have ignorance eliminate you!
 

James Knox

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The sections on “Finding Hum...” and “signal tracing” were exactly what I needed - thank you!

You can usually avoid the high voltage plates with the scope - many of those are usually best assessed with the DMM/VOM! So learn WHERE to probe with the scope probes and WHERE to measure with your DMM/VOM probes before just touching the scope probe tip where it may be interesting.

Good advice! In preparation of receiving the scope, I’m “mapping out” my DMM or Scope points on the 3 different amps (DUT’s) I’m trouble shooting.
 

2L man

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Oscilloscope rule #1 is to use only one Ground Reference and always remember that when oscilloscope uses Mains, which has Earth, they are the same and you CAN'T connect scope GR to any voltage!!!

If you connect a Signal Generator to amp input the Scope GR ties to it using Mains Earthing and you don't have to connect the Probe Ground at all and you should detach this "six inch destroyer" when working with Audio frequencies. It is common to put jaws to probe cable but some day jaws will come loose and cause a short circuit...
 

Peegoo

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My newest scope is a Rigol and it's a wonderful piece of gear.

The one thing to keep in mind that will help simplify your learning process is this: a multimeter is like a still-photo camera: it shows you a snapshot of a signal. A scope is like a video camera; it shows you a signal over a period of time.

The ground thing is super important!

Very true. Watch this vid here to get up to speed on that:

 




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