Finally bought a proper scope...should I cut the GND wire ?

[Level42]

Well I had this little scope tool that worked kind of OK, but I figured it was about time for me to get a real oscilloscope.  Looked around a bit and bought me this one:



It's a 2 channel scope, so I can display vector games on it (which will probably be one of the first things I'll try ) and it's 20 Mhz, enough for the arcade PCB's of my preferred age.

It's pretty old, but solid state all the way and working great acc. to the seller.

More when it arrives...

[patrickl]

Cool. I've always seen these things as a bit of magic. I never quite understood what you use them for even though I saw the technicians use them all the time

[Level42]

Nothing magic about them, but I understand what you mean. I had the same feeling when I saw one used by my uncle to fix TVs etc. when I was a kid. I guess he was my big inspiration to go study electronics. Funny thing is he never did a real study but did everything through experience and looking things up.

He's still the better repair man

Later I learned how to operate them during my study and because you have a understanding of what you're looking at through that study, all the magic disappears

Simply put: they display electric signals in a certain timeframe. I bet there are some great explanations about how they work on the net.

[patrickl]

Simply put: they display electric signals in a certain timeframe. I bet there are some great explanations about how they work on the net.

I know what they do and how they work in a technical sense, but I always wondered how they help people find a problem in a PCB. Well up to some point I know that too, but like you said, you know what I mean. It just looks seriously cool when someone uses a scope 

I worked in a computer company when I was a kid and I was seriously sad when they removed most of the scopes and decided that it was cheaper to replace the PCB's.

[rescue161]

Some things can't be trouble-shot using a multi-meter.  Like timing circuits.  If you use a volt meter, you may see the meter fluctuating or hanging around 5 volts, but when using a scope, you can see the square wave of highs and lows and know that the circuit is doing what it's suppose to be doing, i.e., the high of the square wave would be 5 volts for example and the low would be zero.  If the scope showed that it was straight DC (only 5 volts and no drop to zero), then you'd know there was a problem.  You probably wouldn't catch the problem using just a multi-meter.

It's sort of like using a timing light to check the repetition of something, i.e., a fan.  You adjust the timing light until the fan appears to stop, then you look at the adjustment on the timing light to tell you if the fan is within specs.  With the scope, you adjust the scope until you can see a pattern or wave.  If it matches what the specs are, then you know you're good to go.  If it doesn't, then you figure out why.

It is sad that most electronic repair places are moving to board-swapping because it's cheaper to swap a board than it is to trouble-shoot said board.  If you figure in the cost per man-hour to trouble-shoot a board compared to the cost of that board, it's no wonder why companies are getting rid of their scopes.  I'm glad I have and know how to use one.  Give me a schematic and I can fix it (multi-layered PCBs excluded...lol).

[ChadTower]

A meter shows voltage now.  A scope shows voltage over time.  It's the difference between a point and an XY graph.

Or an XY monitor... which is basically a fixed rate oscilloscope.

Cool meter.  One of these days I need to bust out one of mine and learn to use it.  Then decide which of the two to keep.

[patrickl]

But how do you know what the graph should look like?

[rescue161]

But how do you know what the graph should look like?

You're not trying to look at a graph; you're looking at a wave form.  This site shows the basics:

http://www.doctronics.co.uk/scope.htm

[ChadTower]

Well, it is a graph, same concept anyway.  You know what the graph should look like because you know what is supposed to be happening in the part of the circuit you are tracing.  Just like you know what voltages you're supposed to see with the DMM, you know what should be coming out of that pin on that chip relative to ground.  If the waveform doesn't match there is a problem.

[rescue161]

The "graph" so to speak is part of the scope.  It's a constant, so there will be no change in that.  The wave form is what will change.

It's like saying that the LCD screen of a multi-meter will give you the infromation; It will not.  The data will be displayed on the LCD screen.

[Level42]

OK, I received it. The seller threw it in a (too)large box with some crumbled papers.....not enough really. It works OK, but one of the small (calibration) buttons has broken off, one is bent....

Not a big deal really....

Anyway, before I start using it:

I think I remember that at school, our scopes had cut-off ground wires. This was to prevent any ground loops from happening. When I was later doing a work-practice at a company I was using a scope on a Commodore 64 floppy disk drive, and I blew up a part because of such a ground loop.

What do the scope owners around here do ?

[rescue161]

I use the little gray adapters.  We call them cheater plugs.  You know the ones that allow you to plug in a 3 prong plug into a 2 prong outlet.  That way, you don't have to cut the ground pin off of the plug on the scope.

[Neverending Project]

But how do you know what the graph should look like?

For example suppose you want to check a pin on a transient line - like a memory chip that changes quickly over time - to make sure data is being read to or from it. If you probe it with a DMM you won't get an accurate reading because the voltage on the pin moves up and down too quickly for the DMM to measure it. But if you look at the trace of this pin over time you will see a wave, showing you that data (binary in this example) is moving to or from this chip.

[ChadTower]

The "graph" so to speak is part of the scope.  It's a constant, so there will be no change in that.  The wave form is what will change.

It's like saying that the LCD screen of a multi-meter will give you the infromation; It will not.  The data will be displayed on the LCD screen.

No, it's not.  A graph is the combination of grid and data.  The grid is the XY plastic over the screen - the data is the waveform.  A grid without data is not a graph - nor is the data alone a graph.  In strict mathematic terminology, if either one alone is a graph, it is the data and not the grid.

[Level42]

Uhm....guys.....

[rescue161]

No, it's not.  A graph is the combination of grid and data.  The grid is the XY plastic over the screen - the data is the waveform.  A grid without data is not a graph - nor is the data alone a graph.  In strict mathematic terminology, if either one alone is a graph, it is the data and not the grid.

Hey, you're the one who said you didn't know how to use one...    I know how to use mine...

One of these days I need to bust out one of mine and learn to use it.

[Level42]

Let's try it: a vector game on a scope:
[youtube]http://www.youtube.com/watch?v=_1zI8tmQ-T8[/youtube]

[patrickl]

Ha, ha, cool.