Oscilloscopes - test-drb@ccmp.vtda.org

23 Nov 1999

-----Original Message-----
From: Tony Duell &lt;ard(a)p850ug1.demon.co.uk&gt;
To: Discussion re-collecting of classic computers
&lt;classiccmp(a)u.washington.edu&gt;
Date: Tuesday, November 23, 1999 9:43 PM
Subject: Re: Oscilloscopes

...
 > I agree but I would not recommend someone dropping
a couple hundred bucks to
...
   fix an old
20Mhz scope as I am sure they would not limit their use 
It probably wouldn't cost anything like that much... Most older 'scopes
are easy and cheap to repair.

We are talking about someone here who is *unable* to fix his own scope. I am
sure you or I could fix it for under $5 (providing the CRT and flyback are
good)... but in the real world most people *can't* fix their own test
equipment. In fact, most general repair shops aren't able to do a fair
job....

...
   *exclusively*
to vintage minis. A 20Mhz scope in RF/High speed logic
 troubleshooting/design is totally useless. A 20Mhz scope isn't even very 
_Nonsense_. I've done a heck of a lot of troubleshooting on quite modern
stuff using that 15MHz 'scope I mentioned earlier. It all depends on how
you use your instrument and if you know how to interpret the results. 
Tony, I can't see distortion in an oscillator at 61.25Mhz with a 20Mhz
scope.... And I have pioneered *alot* of code cracking on video signals and
that would not be possible with any old equipment.

You *can* do alot of troubleshooting with a 15Mhz scope... but, for
instance, I can't see distortion/FSK data  on a122.7Mhz oscillator/FM
transmitter (that band should mean something to you ;-) ) with a 15Mhz
scope.

Each to his own...  You obviously love working with old test equipment and
support old hardware. I don't see a lot of people out there like yourself
anymore.. [although I have met a few non-gui UNIX administrators that hate
my guts after tossing their servers for NT] ..  I like working on the old
stuff; sometimes even with the old stuff... but I don't bring that into new
world work... That's just me.

...

> good at looking at the color burst of a video signal in any detail. Again, I
...
 > find most folks design/troubleshoot in a variety
of areas and that's why we
...
 > need scopes with all the toys. I don't see Tek
making any more 20Mhz boxes.
...

Maybe not Tektronix, but there are still 20 and 30 MHz 'scopes in the
catalogues. And most of them are horrible -- they don't trigger properly,
etc. You'd be _much_ better off spending the money to fix up an old
Tektronix than buying one of those. Of course if you can afford a new Tek
with all the bells and whistles, well that's great!.

I agree, but old scopes are expensive to maintain for someone who is not
able to repair it himself.

...
 The other thing is that a Tektronix '20 MHz'
scope will, in general
display something useful for signals of a considerably higher frequency
(I've 'pushed' a 50MHz 547 (_really old_) to at least 75 MHz). Yes, the
amplitude calibration is off. All signals look like a sine wave. But you
can still make measurements if you have to. 
MY POINT! I was refering to RF work above... you don't just buy a scope for
old mini digital  work.. If you buy an old scope/20Mhz you automatically
rule out most high frequency analog work and communications. Digital signals
look like sine waves.. ever tried to diagnose a problem with an RF circuit
with a minimum bandwidth scope??? The waveform looks like pure garbage..
Hence, the need for a *real* scope.

...

At least one company seems to define an 'x MHz scope' as : If you turn
the Y gain right up and apply the maximum allowed signal then you'll see
_something_ at 'x MHz'. I am not joking...

Agreed , I have done it with my 2465 (yes, I have had to look at RF higher
than 300Mhz)... In fact, I use to use a dual trace Gould (100Mhz) on 200Mhz
work..... with minor grief. All depends on the application.

Where are you located in the UK?

...
 -tony