21 Jul
2000
21 Jul
'00
11:32 a.m.
-----Original Message-----
From: ard(a)p850ug1.demon.co.uk [mailto:ard@p850ug1.demon.co.uk]
Sent: Friday, July 21, 2000 6:05 PM
To: classiccmp(a)classiccmp.org
Subject: Re: Other useful test equipment (was: RE: Scope use...)
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.
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.
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.
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.
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_.
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.
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.
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...
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