Used oscilloscope considerations

[ABCD]

I see a lot of used scopes claiming they can't say if the unit is calibrated, or what the calibration status is.  If I buy one of these, I may not be able to tell if it is out of calibration or not, or can I?  Another question is with regards to probes.  Most don't come with probes, or power cords for that matter.  How generic are probes?  (I assume power cords are generic enough.)

I'm trying to sort through the many listings out there and those two things (no probes, unknown cal) stick out the most.

[joelby]

Calibration's not always a huge problem, and you can always check if it's not *too* far out of spec using a voltage source and decent multimeter, and a signal generator or oscillator module.

Generic probes are usually okay for most things, but be careful if the oscilloscope has a 'smart' input that detects the type of probe. I have a DSO that doesn't allow the probe divider to be set through the menu, so without the manufacturer's probes or some fiddling/reverse engineering (sometimes it's a specific resistor value to the extra pin, and sometimes it's an I2C/SPI ROM), you're stuck at 1x. If there's a good photo of the probe input you'll be able to see if there are any extra pins around the BNC jack. If you can get a copy of the manual, you'll be able to see if there's a menu option!

[vk6zgo]

Most Oscilloscopes use normal domestic type IEC cables---some very old types had special connectors.
People get very uptight about calibration with Oscilloscopes,but you very rarely need any great degree of accuracy.

You can do a good check on DC coupled voltage accuracy with an AA cell & a DMM.
Just measure the open circuit voltage of the cell,& compare it with the deflection on the screen,with the Oscilloscope on "auto".

1 cycle of 50Hz mains is 20 milliseconds ,or of 60Hz is 16.666 milliseconds.(don't cram your probe into the mains socket,you can pick up enough hum out of the air)

PAL  line sync pulses (& I think NTSC ,too),are 4.7uSecs wide.

If you don't have "Smart" probes,you will have to do the 10X calculation in your head,like everyone did in the old days--it isn't at all hard!

VK6ZGO

[ABCD]

Thanks for the replies.  The scope in question is a 20MHz analog scope, going for around $50.  I guess I can't go too wrong with that.

[Simon]

1 cycle of 50Hz mains is 20 milliseconds ,or of 60Hz is 16.666 milliseconds.(don't cram your probe into the mains socket,you can pick up enough hum out of the air)


VK6ZGO

Had to chuckle at that

[saturation]

A great price, and worth a look.

Although Dave recommends analog scopes as a good addition to your bench, and I would agree, I also know that many are due to fail spontaneously from sheer age.  So you'll have to beware of that even if it works well when you get it.

Thanks for the replies.  The scope in question is a 20MHz analog scope, going for around $50.  I guess I can't go too wrong with that.

[A-sic Enginerd]

For that scope, yeah, probes won't be much of an issue.

But if you start looking at more "horsepower" scopes, definitely pay attention and do some homework on what probes it may / may not require. I picked up an old TDS 380 at an absolute screaming deal, but the probes were like $200+ US a piece. Still a deal, but don't underestimate the cost of probes depending on your needs and scope capabilities.

[ABCD]

A great price, and worth a look.

Although Dave recommends analog scopes as a good addition to your bench, and I would agree, I also know that many are due to fail spontaneously from sheer age.  So you'll have to beware of that even if it works well when you get it.

Thanks for the replies.  The scope in question is a 20MHz analog scope, going for around $50.  I guess I can't go too wrong with that.

Yes, good point, but for my $50 if I get a year out of it I think it'll add immeasurably to my electronics education.

[vk6zgo]

Using an Oscilloscope after not having one,is like putting on a pair of glasses & realising that you were half blind before.
An amazing amount of good work can be done with even the most basic 'scope.

With your Oscilloscope DC coupled,when checking in all sorts of Electronic circuits,you don't have to change from the 'scope to a DMM to check the DC supplies,etc,plus the 'scope will show if there is ripple on the supplies,which a DMM won't.

Another thing that many people do not realise is how useful they can be in purely DC circuits.
With the 'scope in "auto", & a line across the screen,centre the trace vertically,& you then have a large centre-zero DC voltmeter.
Have fun!

VK6ZGO

 

[ABCD]

One more question on probes:  my local electronics store has probes advertised as "20MHz Oscilloscope Probe" and "40Mhz Oscilloscope Probe".  I would guess using the 40Mhz probe would be ok for a 20MHz scope?  (The 20MHz probes are out of stock and there's no ETA on their arrival.)

[vk6zgo]

Yep!

VK6ZGO

[saturation]

Yes, you can't go wrong for $50, and everyday it lives is very cost effective.  If it does go south, fixing it would give you more electronics education.

A great price, and worth a look.

Although Dave recommends analog scopes as a good addition to your bench, and I would agree, I also know that many are due to fail spontaneously from sheer age.  So you'll have to beware of that even if it works well when you get it.

Thanks for the replies.  The scope in question is a 20MHz analog scope, going for around $50.  I guess I can't go too wrong with that.

Yes, good point, but for my $50 if I get a year out of it I think it'll add immeasurably to my electronics education.

[A-sic Enginerd]

For the scope you're looking at, it's really no big deal, but just a heads up for the future:

if / when you go looking for a more capable scope, you will want to pay close attention to probes. They can sometimes be some serious cash, depending on your needs and the scope capabilities.

Example: I got a screaming deal on an old TDS 380, but no probes. At the time I was able to get a deal on a probe for it for $200+ US. The total package still turned out to be a screaming deal, but the cost of getting the probe tapped out my budget so I was only able to get one. Sure I could have gotten a lesser probe, but the probe was matched to meet every ounce of capability of my scope so when I need it, I'll have it.



Edit: sorry for the double post. I had the response typed yesterday, but had to walk away from the computer before hitting the "post" button. Looks like one of the kids jumped in before I got back to it. Sheeesh......anyone looking for some 10 yr old twins??    

[ABCD]

A-sic

I've seen those probes for sale on ebay.  I assumed at $200+ they were specialised equipment, and that for a 20MHz unit I was probably OK with relatively generic ones.  I don't know what TDS 380 is, but that with $200 probes is probably some serious equipment.

[saturation]

I did a test of those no name eBay ~$10 Chinese label probes rated to 100 MHz.  You can find the old test by searching the eevblog archives.  They'll serve you well.

A-sic

I've seen those probes for sale on ebay.  I assumed at $200+ they were specialised equipment, and that for a 20MHz unit I was probably OK with relatively generic ones.  I don't know what TDS 380 is, but that with $200 probes is probably some serious equipment.

[A-sic Enginerd]

A-sic

I've seen those probes for sale on ebay.  I assumed at $200+ they were specialised equipment, and that for a 20MHz unit I was probably OK with relatively generic ones.  I don't know what TDS 380 is, but that with $200 probes is probably some serious equipment.

Yep. That's why I say for your current application, they should be fine. Was meant as just a heads up for later down the road.

TDS 380 is an older Tek 400 MHz, 1GS/s.

And yeah, the probes in question were pretty much for just that scope. But the point still holds true. When you start looking at bigger "horsepower" scopes, the probes will start getting more spendy.

[ABCD]

Well, it's here, a Hitachi V-222 20MHz analog scope.  It is from a university's physics department, where they're replacing them with digital models.  Haven't had the opportunity to turn it on yet, will try that over the weekend.  Looking forward to it, and thanks again everyone for the advice.

[EEVblog]

Well, it's here, a Hitachi V-222 20MHz analog scope.  It is from a university's physics department, where they're replacing them with digital models.  Haven't had the opportunity to turn it on yet, will try that over the weekend.  Looking forward to it, and thanks again everyone for the advice.

Ah, the V-222 is an excellent entry level analog scope.
I remember the Hitachi's had one of the brightest and sharpest traces of their day.
Enjoy!

Dave.

[Bored@Work]

Haven't had the opportunity to turn it on yet,

Don't turn it on, take it apart!

[ABCD]

Ah, the V-222 is an excellent entry level analog scope.
I remember the Hitachi's had one of the brightest and sharpest traces of their day.
Enjoy!

Dave.

And indeed it is a bright display.  I'm pleased to announce that it works.  I must say Dave, I was losing faith in your $50 ebay analogue oscilloscope, but they do exist.  To anyone else looking for one, be patient and keep checking.  They're out there.

[EEVblog]

$15, no bids:
http://www.ebay.com.au/itm/BK-Precision-2160-60MHz-2-Channel-Analog-Oscilloscope-/360372332978?pt=BI_Oscilloscopes&hash=item53e7dd69b2#ht_3172wt_1139
and
http://www.ebay.com.au/itm/Ballantine-1066B-20MHz-Dual-Trace-Analog-Oscilloscope-/360372333020?pt=BI_Oscilloscopes&hash=item53e7dd69dc#ht_3154wt_1139

Dave.