> >BTW, are there any "buyer beware" questions I should ask and signs I
> >should look out for while buying a used analog scope?  Are there
> >certain parts that always break?  How important is calibration for
> >non-critical measurements?

Calibration is normally good on more "modern"
cros, generally anything 20MHz dual trace or 50MHz
dual trace will have ok calibration, even the cheap
asian brands. I've owned a few.

As they age the electro caps can get ESR faults,
these change performance over time and heat. Most
typically the symptoms are that the timebase or
vertical amp will change over time, so a 10v dc
input may start ok reading 10v than read 10.5v
when the cro is hot. (or freq change) This only
takes 10 mins to test. Also check with a hard
to trigger signal and adjust the triggering so
it JUST triggers, then wait for it to get hot and
see if the triggering circuit goes iffy.
A good signal for this is a composite video from
an AV plug on a VCR etc.

The MOST COMMON fault is "scratchy" pots, like
an audio pot they "crackle" when moved and will
cause movement or jumping of the trace. Watch the
trace while you wiggle and slowly turn the pots.
Sometimes that can be fixed by spraying with
pot cleaner, but likely they will never be perfect
again.

Also look for any burnt-in lines across the screen
showing the cro has seen long hours of use.
:o)
-Roman

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