Other useful test equipment (was: RE: Scope use...)

From: Corda Albert J DLVA <CordaAJ_at_nswc.navy.mil>
Date: Fri Jul 21 18:32:07 2000

> -----Original Message-----
> From: ard_at_p850ug1.demon.co.uk [mailto:ard_at_p850ug1.demon.co.uk]
> Sent: Friday, July 21, 2000 6:05 PM
> To: classiccmp_at_classiccmp.org
> Subject: Re: Other useful test equipment (was: RE: Scope use...)
>
>
> > One last word on test equipment. Unless you are into vintage
> > test equipment collecting (a very respectable hobby in it's own
> > right!) I suggest that you try to get the most modern/reliable
> > version you can _reasonably_ afford, especially if your point
>
> Relaible, sure, but not necessarily modern.
>
> Often the choice (at least for a hobbyist) is between an
> older high-class instrument (like a Tektronix 'scope) and a more modern,
> cheaper, and much worse instrument.

I agree with this in concept. What you're shooting for above
all is _quality_ of design. My point was that given 2 O'scopes,
One by HP and One by Tektronix (both quality manufacturers)
approx. same condition and at approximately the same price,
I would lean towards the one with the newest fabrication date.
This is especially true if you are considering 2 scopes of the
same model/manufacturer. The newer model will most likely have
the newest engineering revisions/mods.
 
>
> Take the better one _every time_. You may have to spend a
> couple of days repairing it, but after that it will be reliable
> again. And it will work properly.

Here again, I agree with this in principle. My only comment is that
you should _know_ what you are doing if you buy a 'Scope with
problems. If you feel comfortable with your ability to repair
this level of equipment, you can end up with some real bargains!
But then again, I didn't target the original post to those people,
as they already know what they are doing. If you look at the root
message that this thread was derived from, it concerned someone
asking on how to "use" a scope to debug digital hardware.
We must keep in mind that a lot of people on the mailing list are
"digital" experts (except for all you PDP-8 owners with "real"
Transistor logic flipchips :-), and most older scopes are as far from
"digital" internally as you can get. Different worlds.


> You will be able to trust the results you get from it. Some
> hobbyist-grade instruments couldn't possible give sensible results !
> A lot of cheap 'scopes don't trigger properly -- I have seen one that
> can't trigger on a 1kHz TTL square wave (!). And without a
> decent trigger
> system you won't get a stable trace, and without a stable
> trace you can't
> make measurements.
>
> My first 'scope was a Solartron CD1400. Old, valved, and not
> particularly
> high spec (15MHz IIRC). I spent a good few days tracking down
> the open
> resistor on the timebase PCB. After I'd done that I had a 'scope that
> worked and which still works some 20 years later (it's needed _no_
> repairs in those 20 years). Having seen some of the modern
> 'cheap scopes'
> (that would have cost about 20 times what I paid for the
> Solartron), I
> know I made the right decision.
>
>
> > in obtaining it is to use it to debug something else. This goes
> > for O'scopes as well as Logic Analyzers, meters, etc.
> > As any engineer will tell you, you want to reduce the number of
> > variables in a problem you are trying to troubleshoot, and the
> > last thing you need in such a situation is a piece of test
> > equipment that you can't trust. Also be realistic in your
>
> True. But don't make the mistake of thinking that a new instrument is
> _necessarily_ a trustworthy instrument. And don't make the mistake of
> assuming that if you get 'crazy results' that the instrument
> is working fine, no matter how good a brand it is, and how new it is.
> _Check it_.
>

I couldn't agree with you more! The primary ingredient of troubleshooting
is Common Sense. If your test equipment is telling you nonsense, then
suspect the test gear. Of course, experience is the greatest way to
develop Common Sense.

 
> It doesn't take long to ensure that the 'scope gives a sensible
> trace when tapped on the supply line. Or when connected to a known-good
clock
> generator. And it might save many hours of looking for a
> non-existant fault!
>
> It is well worth learning how to verify that your instruments
> are giving sensible results. Not necessarily knowing how to calibrate
> them (because 99% of the time you don't need accuracy). But at least
> to ensure that they're not out by a factor of 10. Or that the 'scope
> hasn't suddenly lost all high frequency response, or that it's ringing
> like crazy on a sharp edge.
>
> > selection. If you have a choice between an 1997 Fluke DVM (in
> > good condition) and a 2000 "Bonusmart blisterpack special"
> > you might be much better off choosing the Fluke from a
> > reliability/dependability viewpoint.
>
> Err, 1997 is not old. Any Fluke meter that didn't last at
> least 10 years would disappoint me...

Agreed... I just picked that date at random. I still use an
analog meter (Brain Rot has caused me to block out the Manufacturer
at the momement... perhaps a Triplett Mod 260? Black thing with a
mirrored scale...oh well :-)when working on some circuits. It's
older than sin, but as far as I'm concerned, it's one of the
best analog meters around.

>
> Given the choice between a 1960's Fluke/Solartron/HP and a modern
> no-name, I'd probably take the older instrument. Spend a few
> days getting it back to rights. And then know it would carry on working.
>
> -tony
>
Received on Fri Jul 21 2000 - 18:32:07 BST