how to troubleshoot?

[Happy Harry]

Not a stupid question in the least.

I'd start with a 6V (or so) AC transformer. Look at the AC
line. The transformer gives you isolation from the line so it
is safe to look at the secondary.

DO NOT LOOK DIRECTLY AT THE AC LINE ! This can either
hurt you, or the scope, or both. There are special techniques
for this.

Now see if the AC sine wave is 16.6 milliseconds in period.
If yes, the horizontal time base is reasonably accurate.

Usually a 1KHz square wave at about 1V p-pk is used for vertical
tests. With the probe adjusted properly, the square wave should
be very square.  The wave may overshoot, or undershoot and that means
that the scope probe should be adjusted until the wave is square.

You need to know that the wave you are using is square to start with.
A nice TTL flip-flop will give 50% duty cycle and a nice square wave.

Then measure some known DC voltages and see if the vertical is reasonably 
calibrated.

Its often OK to use the scope for "relative" measurements. You will
still see the waveshapes, even if the cal is not perfect. This is
WAY better than "no scope" !!!

H^) harry


>From: "Jon Darby" <jdarby at lplizard.com>
>To: "Synth-Diy" <synth-diy at node12b53.a2000.nl>
>Subject: Re: how to troubleshoot?
>Date: Mon, 15 Jan 2001 10:33:45 -0500
>
>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?
>
>Your pal,
>Jon
>
>-----Original Message-----
>From: patchell <patchell at silcom.com>
>To: Linc at christeld.freeserve.co.uk <Linc at christeld.freeserve.co.uk>
>Cc: Synth-Diy <synth-diy at node12b53.a2000.nl>
>Date: Saturday, January 13, 2001 12:09 PM
>Subject: Re: how to troubleshoot?
>
>
> >    I have a digital scope at work, don't remember the model number, but 
>a
> >500MHz BW, 1GS/s Tek scope.  Real nice scope......BUT....aliasing can be 
>a
>real
> >problem.  A good example is what I am doing right now.  I am trying to
>track
> >down an oscilation in a power amplifier that drives a three phase motor.
> >Depending on how I set the sample rate, the display looks completely
> >different.  The oscilation is about 1MHz and the signal that is supposed 
>to
> >come out is 500Hz.  The oscilation can look real funny, depending on how
>close
> >it happens to be to a ratio of the sample rate.  I generally have to turn
>the
> >sample rate knob (which also sets the equivalent to the sweep rate) in
>order to
> >make sure I get a "good idea" of what is really going on.  I have gone 
>down
> >many blind alleys because I failed to realize that the scope was lying to
>me.
> >Analog scope don't have this problem.  Still, as long as you know that 
>the
> >digital scope will lie, you can be careful.
> >
> >    Personally, my home scope is an analog.  It is only 20MHz bandwidth,
>but
> >that seems to be more than adequate for synth work.
> >
> >    -Jim
> >
> >Lincoln Fong wrote:
> >
> >> >>However if you got cash to spend get a digital so u can upload upload
>the
> >> results to the pc/mac(now were talking 1000$ range)
> >>
> >> I have always used analogue scopes and whilst talking about upgrading 
>the
> >> other day with a friend he mentioned that a good analogue is sometimes
> >> better than a digital. I think it was something to do with the
>quantisation
> >> causing difficulty taking readings(?). Do you scope afficianados have a
> >> preference? Its mainly for audio work which may have an influence. My
> >> current one is 20MHz.
> >> pc uploading is not necessary.
> >>
> >> Lincoln
> >>
> >> Ps without wanting to start another acronym bonanza what does AFAIK 
>stand
> >> for???
> >
> >--
> > -Jim
> >------------------------------------------------
> >* Visit:http://www.silcom.com/~patchell/
> >*-----------------------------------------------
> >*I'm sure glad Merry Christmas comes just once a year
> >* -Yogi Yorgensen
> >------------------------------------------------
> >
>

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