Oscilloscope

[Peter9DO]

Re: Oscilloscope

Oh..... Yea, see if you put DSO scope in you will see the items I'm talking about. It almost looks like the back of a camera. A small portable oscilloscope, with maybe a 3" screen. It looks very cheap and I thought that's what you were talking about.

In the last few days I have someone that I have been in contact with regarding a Tektronix Model 2225. I don't think this has a digital storage and it's only 50MHz. I really don't understand the whole MHz even after a whole night of watching oscilloscope videos

[Peter9DO]

Re: Oscilloscope

By the way what model number is the one you have?

[PCBONEZ]

Re: Oscilloscope

Mine is a Tektronix 7633.
Probably out of your price range but you never know... Sh*t happens..
The Tektronix 7000 series are 'frame' type.
Those 3 modules [aka "Plug-ins"] you see under the screen slide out and are interchangeable with others to reconfigure it into various kinds of scopes.
There is even a plug-in to turn it into a spectrum analyzer. [No I don't have that.. LOL]
I do have 7 various modules for it though.
It's 100MHz but there's are modules that upgrade to like 400 or 500 MHz. [I forget because I don't need one.]
There is actually a 1GHz module for the series but I don't think my frame version is compatible with that one.
This guy is an old TEK nut.
http://www.barrytech.com/tektronix/t...000scopes.html
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Mine doesn't have a way to display on a PC if that matters to you.
There were some that did back then but AFAIK they required an ISA card for the interface so you'd have to throw together a vintage PC just for that purpose.
The interface was called GPIB.
For GPIB you need a scope with a GPIB-out, an add-in PC card with a GPIB-in, a GPIB cable, and the GPIB software.
GPIB to USB converters exist but they are rare and usually expensive.
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The Tek 5000 series - too old, don't go there. - Those still had tubes.
Unless of course you LIKE tubes... LOL.
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The Tek 2000 series is a good one for you to look for.
They did have DSO and/or Storage versions.
To check if it's analog or not use google and check in a few places because sometimes the sites are wrong.

The Tektronix 4xx models were also good and came with memory versions but 'light weight' isn't a good description of those.
http://www.ebay.com/itm/220918982982
Those were the most common scope in the Navy in the 80's and 90's.
I've used lots of them. - A little old now but not too bad for a scope.
They are pretty darned rugged as scopes go.
Have to be to get hauled up and down ladders to the work site all the time.

The Tek 2000 series are newer and lighter than the 4xx Series.
Still fairly rugged.
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There are a number of other good brands but finding documentation might be more difficult.
Always check that before you buy.
And DON'T buy a completely 'untested' scope.
- If it at least shows a signal with an input you can probably adjust it in good enough.
Also beware of weak picture tubes. They aren't so cheap.
And, watch out for busted/bent knobs. Common with scopes. Sometimes cheap to fix other times not.
Ideally you want to find the actual service manual before you buy it.
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Were I you I'd save up until you have $400 to throw at this.
Can probably score a 100MHz that's calibrated and/or has a warranty for that much.
In the long run you'll probably be better off.
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Someone [here, another thread] tried an Owon w/LCD screen in 60MHz [I think] and it was at least okay for checking ripple from PSUs.
[edit] er... Maybe it was an Owon knock-off. At any rate it was an LCD screen w/USB and it looked like an Owon... LOL.
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I tried a USB powered Hantek myself and I thought it sucked.
The noise [ripple] in the PC's USB port [meaning the scope's power source] ended up on the screen mixed into the the actual signal.
Kind of hard to measure ripple when you already have ripple on the screen with the probe disconnected.
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[PCBONEZ]

Re: Oscilloscope

I really don't understand the whole MHz even
after a whole night of watching oscilloscope videos

Sorry, I didn't see that before.
The MHz is the Bandwidth.
The scope's bandwidth should be at least three times the bandwidth of the signal to be measured.
In other words a 50MHz scope is good for measured frequencies less than about 16 MHz.
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Also want a sample rate around 10 times the bandwidth.
For a 50 MHz scope that would be at least 500 MS/sec [or 0.5 GS/sec]
- This is so there are enough 'dots' for the scope to figure out an accurate wave form to display.
[Think like connecting dots on graph paper to make a curve. The samples are the dots.]
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A 50MHz scope is fine for measuring ripple [around 50k-300k Hz] but if you ever need to check MOSFETs for ringing it might not be good enough. That can be up in the MHz range [say 10 MHz+] and you really need at least a 1 GS/sec sample rate to be sure of getting a good trace.
Indirectly that means you need a 100MHz scope.
[There could be odd-ball 50MHz scopes with a 1GS/sec Sample Rate that would work but 'Bandwidth x10 = Sample Rate' is the norm, at least with older scopes.]
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The above is general, ball-park, rule of thumb and opinion.
Not everyone is going to agree.
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[Peter9DO]

Re: Oscilloscope

Thank you for all the information! Trying to pick out a scope has proven itself to be much more annoying than it should have been! I really do think my budget has a lot to do with it. I know I should think about moving the budget up some but I just don't know how frequently I will use the scope so I really don't want to pay a lot of money for it. Well I have been going back and forth with a gentleman regarding a Tek 2220 which has a digital storage on it (going off of your advice about the digital storage) although it's only 60MHz. The guy wants a little to much for it though at $250 with no probes, I have found this same scope on eBay in the $150 area. I'm going to see if he will come down in price some.

All in all, how do you feel about the Tek 2220? As I said I normally work on laptops but am venturing out and have been doing work on LCD TVs and plasmas as well. All the service manuals claim that a oscilloscope is needed to test waves. Also, would I need a function generator for what I'm trying to do?

[Peter9DO]

Re: Oscilloscope

WOW! I can't believe how many modules they made for these! Now that's crazy!

[Agent24]

Re: Oscilloscope

Oh..... Yea, see if you put DSO scope in you will see the items I'm talking about. It almost looks like the back of a camera. A small portable oscilloscope, with maybe a 3" screen. It looks very cheap and I thought that's what you were talking about.

I would assume you are talking about ones like this?
http://www.seeedstudio.com/depot/mic...ano-p-512.html

They generally top out at about 1Mhz, so pretty useless.

[Peter9DO]

Re: Oscilloscope

I would assume you are talking about ones like this?
http://www.seeedstudio.com/depot/mic...ano-p-512.html

They generally top out at about 1Mhz, so pretty useless.

Precisely!

[PCBONEZ]

Re: Oscilloscope

A Tektronix 2220 would do fine as a first scope if it 'runs'.

So far as how frequently you will need the scope, probably not as often as you think.
There -ARE- some things you can't check without one but they don't come up every day.

For instance, as you do laptops, how much ripple is that power brick sending out?
Being able to check can save you a lot of time and avoid replacing good power bricks just because you aren't sure about the old one, ,
, but how often does that come up for you?
I can't know that.
I'd say if it saves you from tearing apart or replacing something like 10 power bricks [that didn't need fixed] it will have paid for itself.
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Same thing with PC and screen power supplies.
You don't -really- know if they are good without checking the ripple.
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Yes for signal tracing you would need a signal generator of some kind.
It doesn't have to be fancy though and there are actually schematics for DIY basic ones online.
One that simply output a square wave at various frequencies would be good enough for most things.
Can't see that coming up too much though.
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[Agent24]

Re: Oscilloscope

Sorry, I didn't see that before.
The MHz is the Bandwidth.
The scope's bandwidth should be at least three times the bandwidth of the signal to be measured.
In other words a 50MHz scope is good for measured frequencies less than about 16 MHz.

This is something I have not yet understood. Why can't a 50Mhz scope display a 50Mhz waveform? Or can it?

If it can only measure 16Mhz signals well, why is it not called a 16Mhz scope?

Is it all just down to marketing?

[PCBONEZ]

Re: Oscilloscope

I don't understand why they do it that way myself.
The 50MHz is the bandwidth of the 'guts' of the scope. [Not what you are measuring.]
The 3x thing has something to do with avoiding errors due to harmonics.
16MHz could have harmonics at 32 and 48 MHz so 3x only covers the first two [the most likely] higher harmonics.
Could also have harmonics at 8MHz and 4 MHz on the lower side.
- So lets say you are measuring 48Mhz with a 50 MHz scope.
- If you don't have the 3x margin how do you know you aren't actually looking at a low harmonic of 96MHz in the circuit?
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That might not make any sense, I just woke up...
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About the time the theory gets that deep I go goo goo eyed and push the 'I believe' button because I'm getting bored with it.
I'm not out to design a scope.
All I wanna know is what I need to measure what I want and 3x is what 'they say'.
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[Th3_uN1Qu3]

Re: Oscilloscope

I don't understand why they do it that way myself.
The 50MHz is the bandwidth of the 'guts' of the scope. [Not what you are measuring.]
The 3x thing has something to do with avoiding errors due to harmonics.
16MHz could have harmonics at 32 and 48 MHz so 3x only covers the first two [the most likely] higher harmonics.

The rated bandwidth of an oscilloscope is the SINEWAVE bandwidth. A pure sinewave has no harmonics. If you're trying to measure a switching signal which is usually a square wave, you need to be able to accurately measure at least the 3rd harmonic as well (tho catching up to the 5th is preferable), so you need your scope to have at least 3x the bandwidth of the signal you are measuring.

[PCBONEZ]

Re: Oscilloscope

The rated bandwidth of an oscilloscope is the SINEWAVE bandwidth. A pure sinewave has no harmonics. If you're trying to measure a switching signal which is usually a square wave, you need to be able to accurately measure at least the 3rd harmonic as well (tho catching up to the 5th is preferable), so you need your scope to have at least 3x the bandwidth of the signal you are measuring.

Sort of.

I read about that elsewhere before but it wasn't explained as well there.
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~So~
For analog you want 3x.
For digital [like a square wave] you want 5x.
So a 50MHz scope would only be good for [at most] a 10Mhz square wave.
[And no matter what, more scope bandwidth is better.]
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Below are some visuals out of the PDF.
A 100 MHz square wave on various bandwidth scopes.
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100 MHz square wave on a 100 MHz scope. [1x]


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100 MHz square wave on a 500 MHz scope. [5x]

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100 MHz square wave on a 1 GHz scope. [10x]

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100 MHz square wave on a 2 GHz scope. [20x]

[Peter9DO]

Re: Oscilloscope

A Tektronix 2220 would do fine as a first scope if it 'runs'.

So far as how frequently you will need the scope, probably not as often as you think.
There -ARE- some things you can't check without one but they don't come up every day.

For instance, as you do laptops, how much ripple is that power brick sending out?
Being able to check can save you a lot of time and avoid replacing good power bricks just because you aren't sure about the old one, ,
, but how often does that come up for you?
I can't know that.
I'd say if it saves you from tearing apart or replacing something like 10 power bricks [that didn't need fixed] it will have paid for itself.
.
Same thing with PC and screen power supplies.
You don't -really- know if they are good without checking the ripple.
.
.
Yes for signal tracing you would need a signal generator of some kind.
It doesn't have to be fancy though and there are actually schematics for DIY basic ones online.
One that simply output a square wave at various frequencies would be good enough for most things.
Can't see that coming up too much though.
.

Yea, these issues don't come up that frequently for me, but again I think it would be nice to have it on the bench if I need it, at least it's there you know what I mean!

Now to the extent of your conversation about the 3x grater I will keep my eye out for any deals I may find that are a little better. I'm really not in a rush to buy one and I would like to hold off to get one that is right for me at the price I can afford. As you have mentioned I will need to buy a function generator as well (or build one). This is going to get expensive, I can feel it!

Thanks again guys for all the help with this stuff! I will be asking for lessons next! lol!!!!! No, I'm kidding but I'm sure I will have some questions on how to use it from time to time.

[PCBONEZ]

Re: Oscilloscope

Yea, these issues don't come up that frequently for me, but again I think it would be nice to have it on the bench if I need it, at least it's there you know what I mean!

Now to the extent of your conversation about the 3x grater I will keep my eye out for any deals I may find that are a little better. I'm really not in a rush to buy one and I would like to hold off to get one that is right for me at the price I can afford. As you have mentioned I will need to buy a function generator as well (or build one). This is going to get expensive, I can feel it!

Thanks again guys for all the help with this stuff! I will be asking for lessons next! lol!!!!! No, I'm kidding but I'm sure I will have some questions on how to use it from time to time.

I think if you hold out for a good deal you can score 100MHz used scope in your price range without too much problem.
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O'scopes have a test signal point built into them [it's usually a 1v 1kHz square wave provided to adjust the probes] so if some ad doesn't show an actual signal [vice a flat line] then don't assume the scope works. A scope can show a flat line without processing any input signals at all.
Alternately if the ad says it passes it's self-check [which some scopes have built in] then it's probably okay.
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You want the -SERVICE- manual for it. Make sure you can get one.
That will tell you how to adjust and calibrate it yourself - although for some things you'll need additional equipment or parts.
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I went with Tektronix partly because they made zillions so parts are still available.
There are definitely other good brands.
I just dunno much about parts support for those brands I don't have.
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[Peter9DO]

Re: Oscilloscope

So I bought the Tektronix 2220 O-scope today!!!!! 60Mhz, 2 Chan, with digital storage.

First of all I was so impressed at this guys set up! It was unbelievable! 4 work stations with scopes, soldering and DESOLDERING stations, hot air, power supplies and everything else you would want at each station! Need I say this is all in his basement. Not gonna lie, My jaw hit the ground, especially when I saw Hakko desoldering stations at each station, that's got to run close to $600 each..... wow!

Anyways, he gave me a crash course on how to use it, he had a 100MHz and this 60MHz he said that he really thinks that the 100MHz would be overkill for what I'm trying to use it for. That the 60MHz would do just fine. I bought the unit with no probes for $200.

Now, my question is I need to buy probes, I was looking on eBay, and I was wondering am I able to put 100MHz probes on a 60MHz scope?

[PCBONEZ]

Re: Oscilloscope

I was wondering am I able to put 100MHz
probes on a 60MHz scope?

Yes.
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Here are the specs for the 'stock' probes for that.

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Need to get probes with a compensating range that covers the input capacitance.
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Need to get probes with the correct input resistance.
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Both the above are different between 1x and 10x probes.
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You probably want at least one of each of 1x and 10x or one with a 1x-10x switch.
[If you connect to 50v with a 10x probe the scope only sees 5v.]
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When you get the probes connect to the test signal and adjust the compensation for a nice square square-wave on the screen.
[That takes out error due to the cable size and length and the probe.]
The adjuster is usually a very small screw. Location varies.
Could be near the connection to the scope or on the probe itself.
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[PCBONEZ]

Re: Oscilloscope

Here's the Op manual.

Good luck with the Service manual.
I didn't find that one.
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[TheLaw]

Re: Oscilloscope

I just snagged a 100Mhz Tek 465M for $70 shipped off eBay.

It's sweet.

[Agent24]

Re: Oscilloscope

Now, my question is I need to buy probes, I was looking on eBay, and I was wondering am I able to put 100MHz probes on a 60MHz scope?

Just make sure you get good ones.

There are "100Mhz" probes on eBay from China for like $7... rubbish, don't even bother

Sort of.

I read about that elsewhere before but it wasn't explained as well there.
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~So~
For analog you want 3x.
For digital [like a square wave] you want 5x.
So a 50MHz scope would only be good for [at most] a 10Mhz square wave.
[And no matter what, more scope bandwidth is better.]
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Below are some visuals out of the PDF.
A 100 MHz square wave on various bandwidth scopes.

Looks interesting, I think I get it now