'Scope has arrived...triggering?

[Matt T.]

Thanks for the help in my other o-scope thread. I ended up getting an older SS 20MHz Kenwood CS-1021 for $59 plus almost as much for shipping...plus almost as much again for a 10x/1x probe with all the tips. Now I need some help checking it out to make sure it's functional (it was advertised as fully functional).

First off...power cord has ground prong missing and it affects the scope. I attached an alligator clip to a chassis screw and grounded that...and that made a difference. I have power cords and will put a good cord on it soon enough (if I keep it).

All knobs/switches appear to function...they all have some sort of affect on something and many of them are (I'm pretty sure) functioning fine.

I did the probe compensation procedure using the front panel test point and was able to complete that successfully no problem. I was able to get the display to show just a few cycles and to be stable and in a fixed position on the screen. Does that right there mean that the scope is triggering properly? It was in Auto mode at the time.

This triggering business is what I'm most concerned about (at least for checking the functionality of the unit). I've been trying to 'look' at the waveform put out by my metronome when set to 'tune'. In 'tune' mode the metronome puts out 440Hz, or 441Hz, or 442Hz, etc. and this tone is adjustable via the volume control. I plugged into the headphone jack of the metronome and took the signal from the tip and sleeve of the cable. I can't get this to look much like anything coherent. The trigger controls do affect it...sometimes...and I can certainly make it look worse but I can't get a smooth, focused waveform on the screen. Should I be? I tried adjusting the metronome volume and it had no effect...tried flipping all sorts of switches and turning the trigger knobs and they usually do something...but still not a smooth waveform.

I do not have a signal generator yet...I was hoping to use the metronome for now (I also have a digital keyboard).

I did read some stuff on o-scopes before it arrived and since...but I'm just not 100% sure that it's functioning correctly. It's probably just pilot error. Any help appreciated.

BTW - compared to new stuff this older stuff just feels SOOOOO solid. Couple of trimmer pots have bent shafts but work perfectly.

[Ray Ivers]

Matt,

First off...power cord has ground prong missing and it affects the scope.

FWIW, I had my old 'scope ground-lifted using an adaptor for practically the whole time I used it, and my current 'scope is designed not to be grounded. My signal generator came with a 2-prong power cord, which I've never changed.

This triggering business is what I'm most concerned about...

IME triggering issues are the #1 'WTF factor' for many 'scope users. I struggled through my first year of ownership before figuring out how to get external triggering to work well, and more than one customer with a 'scope at home has asked me, "how do you get your display to remain so stable?"

Here's what I did: I added a second BNC output jack to my signal generator, and connected it to the top & ground of the output level control. Then, I ran a cable from the new jack to the 'EXT TRIG' input of the 'scope, set the trigger selector to 'EXT', and never looked back. Now the 'scope receives a continuous high-amplitude trigger that does not vary with adjustments of the signal generator's output level. If the signal generator already has a fixed-level output available, this won't be necessary.

I do not have a signal generator yet...I was hoping to use the metronome for now (I also have a digital keyboard).

IMO a 'scope has very limited functionality without an accompanying function generator. I found this one via Google - no idea how good it is, but I doubt you'll find a new one much cheaper:

http://functiongenerator.hobbytron.com/EFG500K.html

Ray

[Matt T.]

Thanks Ray...that signal generator is a kit so I'd have to build it...but the price is right (I just really want to start using/learning the scope instead of building something else). When I look on e-bay I see a lot of RF stuff and a lot of really expensive stuff. It looks like I would spend several times what I spent on the scope just for a used signal generator that goes low enough for audio. I guess I just didn't expect to have to spend so much on the signal gen. (it just seems like it's the 'cheap and simple' part).

[Ray Ivers]

Matt,

I just really want to start using/learning the scope instead of building something else.

Understood - unfortunately, IMO you really need the function generator to use the 'scope; otherwise, I wouldn't have suggested it. The assembled F.G. version is around $50, but - let me guess! - that's way too much money to spend.

I've seen it personally at least half a dozen times; someone gets a 'scope but can't be bothered with the "optional" function generator, they have difficulty getting the 'scope to display anything really useful, and it ends up gathering dust in a corner.

I'm not getting down on you, Matt, just trying to ensure you get a decent return from your new investment, based on almost 30 years of using 'scopes for both work and play.

Ray

[Euthymia]

If you are really broke and need a function generator, build one of these on perf board:

http://www.euthymia.org/DIY/Eriksosc.jpg

Even if you use no surplus parts, you can keep the cost down under $15. Use a plastic box from Radio Shack as an enclosure.

Jameco has the XR2206 for $3.29.

[Satamax]

Matt, i reiterate, try sweepgen! If you need more voltage from your sound card, use a mono or stereo solid state or tube amp to amplify line signal.

http://www.david-taylor.pwp.blueyond...are/audio.html

[Matt T.]

Thanks for the help. I'm not as cheap as I appear to be...I actually just paid for a used one for $99...ooooh...big spender! I was overwhelmed by the uber-expensive units and the plethora of non-AF units for cheap...but once I looked around I found one that will do AF for reasonable. Ray appears to know exactly what I'm going through...I guess he's seen it a bunch of times.

Satamax...I appreciate the suggestion but I'd really like to keep my computer out of this. I guess I'm just too 'old school' and prefer to NOT use a computer if I can help it. It's amazing what a pencil and paper (for example) can do and the speed at which you can do it but I think everybody forgot. My computer is pretty much just a fancy poker table (and youtube viewer) anymore. Everything is fine until I need to do the simplest of tasks but for whatever reason end up spending 2 hours 'configuring this' or 'loading that' or whatever...then I realize it would have taken about a minute and a half to use pencil and paper. Rinse and repeat a hundred times and I finally caught on...don't use it unless you have to.

[bob p]

Congrats on your new scope purchase. You're about to learn the hard way that you're going to fall victim to the TEARGAS syndrome -- Test Equipment and Repair Gear Acquisition Syndrome. As a result of buying a scope, you'll find that there's all sorts of other stuff that you need to buy now.

I think that Ray makes a valid point about how much other stuff you'll need that you may not have planned on buying -- At an absolute minimum you NEED a good function generator, probes, patch cables, and dummy load resistors. For some things a second signal generator is useful. To really understand how your scope works, get hold of a second signal generator (borrow one or buy the $25 kit Ray mentioned), and learn to draw some Lissajous Figures.

I predict that it won't be long until you find yourself in need of a frequency counter, a distortion analyzer, etc.

BTW -- Ray, that's a SMOKIN' deal on the inexpensive signal generator kit. If I hadn' already bought two signal generators, I'd buy that kid for my second one.

[Ray Ivers]

Bob,

Yeah, the test gear really can build up after a while... at some point I really would like to get a top-notch benchtop multimeter, but the new 'scope comes first.

BTW -- Ray, that's a SMOKIN' deal on the inexpensive signal generator kit. If I hadn't already bought two signal generators, I'd buy that kid for my second one.

I thought so too! I was thinking of getting one as well, but I came across a tiny Motorola unit I had stashed away that I think I'll modify for trigger-out and put it in my toolcase for roadwork instead.

IME there's just no way around the requirement for a function generator along with the 'scope. I remember trying to squeak by with tuner/keyboard outputs ("WTF kind of waveform is this ??"), 'scope calibration signals (clip-terminal output, square wave only, no level control, etc.), hi-fi calibration tones, etc. - then I got the generator and everything fell right into place.

Ray

[bob p]

When I bought my used scope I ran into one of those chicken/egg conundrums: You need a function generator to test your scope, and you need a scope to test your function generator.

I had a "new" used scope in-hand and I had 72 hours to decide to keep it or send it back. Unfortunately I had no signal generator and the one I had bought on eBay wasn't going to arrive in time. The situation could have easily been reversed -- signal generator in hand but no scope to test it with. As a quick test, I traced the LFO on a trem circuit to verify that the scope had survived the ride on a UPS truck.

Because I was buying used gear I had to drive an hour to go to a friend's house so that we could put the scope through its paces. Though buying new is always more expensive, its always easier to buy new, and when you buy used there are those hidden costs that you forget to factor in, like driving to your buddy's house to check something out.

Then, of course, once you finally have all of your gear, Murphy's Law takes over -- you have a completely equipped test bench, but something breaks and you don't have a backup for everything... The need for backup gear always works as a good rationalization for buying more stuff!

[Matt T.]

BTW - bob those Lissajous figures look very cool. I was gonna make a 'spirograph' joke (remember those?) but nah...they look tres cool.

I did some very light reading on them...I guess they appear to 'rotate' (in a 3D sense) and that the direction of rotation is...what's the word...merely a 'perception' and could be in either direction (or both...or it might switch directions arbitrarily).

[Enzo]

They can even be useful to match or measure freqs. The ratio between the number of times the trace hits the side edge and the top edge is the ratio between the sweeping freqs.

[Mark Black]

Another signal generator possibility - these guys seem to have knocked off the Rolls unit for even less money:

http://www.mcmconnect.com/tenma/prod...C4767E3FB6E204

One attractive feature (for MI amp testing) is that outputs are on 1/4" jacks, as opposed to the more common banana or BNC connections on "real" test gear. Another thing is that it is powered by a "wall-wart", so has no potential for ground-loops (depending on other connections).

Also if it truly copies the Rolls unit the output can be taken all the way down to "0", which neither of my B-K units will do (aggravating sometimes).

[bob p]

BTW - bob those Lissajous figures look very cool. I was gonna make a 'spirograph' joke (remember those?) but nah...they look tres cool.

I did some very light reading on them...I guess they appear to 'rotate' (in a 3D sense) and that the direction of rotation is...what's the word...merely a 'perception' and could be in either direction (or both...or it might switch directions arbitrarily).

If you don't mind, I'm gonna hijack your comments and follow up to them in that other thread (to keep things on topic).