Tektronix 2225

[SuperMiguel]

A local person is selling an Tektronix 2225 in good conditions for $75... Should i just jump into this? or should i save to get the rigol 50 Mhz one?

[GeoffS]

Go for it!
If it's in good condition, it's worth more than $75.

[DJPhil]

Honestly I'd consider both. I've been saving for a Rigol since March, but bills keep popping up, though I did jump on an old 465B for twice that price. There's nothing wrong with having two scopes, especially one analog and one digital as they have different strengths in the low budget price range (low noise vs. single shot capability and auto measurements). If it's truly in good shape then $75 is a good price. You can probably find old analog scopes with more bandwidth (100MHz to 200MHz is fairly common), but it can be a pain to find one locally depending on where you are.

Whenever I finally save up and buy a DSO, I won't be sad at all to have a solid analog to go with it.

[SuperMiguel]

I have never use a scope before, so maybe its good ohysically but prob someyhing broken inside, I would not know, how can test it? Remember I never used one before, and this on has alot of buttons

[allanw]

At the very least make sure it turns on and that you can see two horizontal traces on the screen. I'd say $75 is about the going rate for 2225's on ebay, so it's not that great of a bargain.

[SuperMiguel]

do i have to do anything to see the horizontal lines?

[Simon]

make sure it is set up correctly  essentially you should get two lines by turning it on and selecting both channels. there should be a test output, get you friend to connect it up so that you can see it working of it's own internal calibration signal generator

[djsb]

I've got a 2225 and the service manual to go with it (available from Mauritron services). It's a good scope and easy to use. The switch contacts may need a good cleaning with Servisol contact cleaner though if you buy it.

[saturation]

If you can get a good 5MHz square wave to put into both channels, and compare them against the same at 1kHz, you can eyeball frequency response easily.  It should check all the scopes basic capacity in one test.

[Mechatrommer]

A local person is selling an Tektronix 2225 in good conditions for $75... Should i just jump into this? or should i save to get the rigol 50 Mhz one?

pay and take it, fast! dont ask any question! save money for rigol later...

this one selling calibration i think (USD395), and shipping ~= 2x calibration price... http://cgi.ebay.com.my/Tektronix-2225-50-MHz-2-channel-scope-NIST-certified-/350356739114?pt=BI_Oscilloscopes&hash=item5192e3942a

and this one shipping is more than 4x the unit price (USD90)... http://cgi.ebay.com.my/Tektronix-2225-Oscilloscope-/250657328526?pt=BI_Oscilloscopes&hash=item3a5c574d8e

[SuperMiguel]

If you can get a good 5MHz square wave to put into both channels, and compare them against the same at 1kHz, you can eyeball frequency response easily.  It should check all the scopes basic capacity in one test.

How do I generate that signal?

[TheWelly888]

Word of warning - check the focus, brightness, horizontal course and fine pots first - if worn the replacement ones are very difficult to get hold of. The 15 odd year old unit I use at work has triggered trace jumping about the screen because the horizontal pots are worn. A few years ago the brightness pot needed replacement and I was VERY lucky to get hold of a replacement pot from Megger because it is no longer made and it was the last one they had!

[djsb]

The one I have had a problem with the focus. The fault was one resistor in the focus chain that had burnt out. I replaced this and everything was OK. I did buy a spare pot just in case.

Sphere research ( http://www.sphere.bc.ca/ ) is a good source of parts and the Tekscopes yahoo group ( http://tech.groups.yahoo.com/group/TekScopes/?yguid=330951138 ) is a good source for help.

[saturation]

You'd need a good function generator, the seller may have one.  How its used:

http://www.google.com/url?sa=t&source=web&cd=2&ved=0CBcQFjAB&url=http%3A%2F%2Fwww.kennethkuhn.com%2Fstudents%2Fee351%2Ftext%2Fsquare_wave_testing.pdf&rct=j&q=square%20waves%20amplifier%20pdf&ei=RvS5TPCnBoGClAe1_7mkDQ&usg=AFQjCNHNMdjks7pxoYwIsqxfSqfc_iR-kA&cad=rja

Although the pdf is about audio amplifiers, the same principles work for a scope's input amplifiers.  To see the tracing well, you'd have to work the controls too, and this would test any problems with them, as well as the quality of the screen.

If you can get a good 5MHz square wave to put into both channels, and compare them against the same at 1kHz, you can eyeball frequency response easily.  It should check all the scopes basic capacity in one test.

How do I generate that signal?

[SuperMiguel]

Got it and everything seems to be working fine... i have a simple question:

When im analyzing a simple LED flashing i only see a dot on the screen, i cant get a line that makes a square wave why is that??

[joelby]

The LED is flashing too slowly for the CRT display persistence to keep up with and display a solid line. Try looking at some higher frequency signals, such as the probe compensation output.

[SuperMiguel]

i did an arduino program with a 10ms flash rate and still not able to see it.

[joelby]

100 Hz is pretty slow. Try a few orders of magnitude faster! Does the probe compensation output on the scope work?

[SuperMiguel]

what do you mean by Does the probe compensation output on the scope work?

not sure what the probe compensation is

[joelby]

Most oscilloscopes have a built-in square wave generator with an output somewhere on the front panel. This is used to tune the capacitance of your probes, which usually have a small tuning knob in them somewhere, to make the squarest-looking square wave.

Looking at a photo of the 2225, it appears that the output is labelled "PROBE ADJUST". Connect the probe to this and the ground to a suitable ground point, such as the outer rim of the EXT INPUT BNC connector, if you have an alligator clip for a ground.

[SuperMiguel]

yes that displays a perfect square wave...

[joelby]

yes that displays a perfect square wave...

Good! The signal you were generating with your Arduino is just too slow. This isn't a problem with the oscilloscope, just the display technology.

[SuperMiguel]

if i just create a on and off program with out a delay.. that will get me 10 Mhz right? wil that be fast enough?

[joelby]

if i just create a on and off program with out a delay.. that will get me 10 Mhz right? wil that be fast enough?

If you're using the digitalOut() functions (or whatever they're called), then possibly not - it's my understanding that these functions have some mysterious overhead and are quite slow, so you'd need to access the port directly the toggle with at top speed. No harm in trying, though - it would be an interesting experiment to calculate how much overhead the Arduino library has for this function by comparing the frequency you get to the theoretical maximum.

[Bored@Work]

i cant get a line that makes a square wave why is that??

Because your signal is to slow.