Scopes 101 was: how to troubleshoot?

[DCMagnuson at aol.com]

In a message dated 1/15/01 10:34:59 AM Eastern Standard Time, 
jdarby at lplizard.com writes:

> Howdy, everyone!
>     Here's a question: I picked up an old tube Heathkit oscilloscope from an
>  R/C airplane convention in Pennsylvania a few years ago knowing I would 
need
>  one some day. Well, it seems to work wonderfully, but my eyes are 100%
>  untrained in in oscilloscopes, so is there a test procedure I can do to put
>  it through its paces and know it is functioning properly? Build a little
>  oscillator with known values and frequency maybe? How do you test an
>  oscilloscope in general? Is this a stupid question?

I think I have the same scope as you do.  (I also have a newer 20Mhz scope).  
The problem you'll find is that the Heathkit scope has no timebase module / 
trigger input.... it's a little hard to stabilize a waveform on the screen 
sometimes.  Otherwise they work fine.  Mine needs some new powersupply caps 
(there's a ripple on the CRT even with the probe tip grounded), so I use my 
other scope most of the time.

If you have specific questions about this scope, feel free to ask me.  As far 
as using your scope, try this... find a stable DC power source, around 2-5V.  

Set your "V/Div" or "Vertical Sensitivity" knob (volts per division.. the 
divisions are the little graph lines on the screen) to a range that is near 
your DC voltage.  Apply the DC voltage to the scope probe.  The flatline will 
jump up to the voltage you apply, so adjust the calibration knob to get it as 
close to the proper division on the screen as possible.  Try a few different 
known voltages, and see if the wave moves to the appropriate spot on the 
screen.

Next, apply a waveform to it.  You can use a freq generator, or even an LFO, 
etc.  Again, set the V/Div knob to the proper range.  Try to get the wave as 
tall as possible without going off the top of the screen.  Now you adjust the 
"Width" control to get the width of the wave to look good on the screen.   
Finally, you may find that the wave is moving on the screen... possibly 
whizzing by at a high rate.  You adjust the "sweep frequency" until the wave 
stops.

Using a square wave is a good idea... you can see any rounding or weirdness 
in the wave very clearly.  It will give you an idea of how good your scope 
is.  That said, my Heathkit scope always slews the wave a little, and the 
tops of the waves aren't perfectly square.  Still, it's a great little scope 
to learn on, because it isn't as full featured (and therefore confusing). 
It's especially nice since it was free (thanks Dad)

Dave Magnuson