You're right, Tony, many of them are cheap because they're incomplete. I
paid over $1k for mine, but it was complete, right down to the manuals and
GPIB/RS232/Epson Printer adapters. It also came with ROM packes and
self-test jumpers.
I've seen plenty of LA's without these, and even a number of
pods/lead-bundles without the LA, in each case worth little without the
"other-half." I wonder why surplus dealers let this happen? They'd get 10x
the money if the equipment were complete.
Dick
----- Original Message -----
From: Tony Duell <ard_at_p850ug1.demon.co.uk>
To: <classiccmp_at_classiccmp.org>
Sent: Friday, July 21, 2000 1:45 PM
Subject: Re: Other useful test equipment (was: RE: Scope use...)
> >
> > Another useful piece of equipment is a multi-channel
> > logic analyzer. Most of these units can read out
>
> Agreed. My Logic Analysers get a _lot_ of use.
>
> > Now, before anyone flames me, I will admit that
> > new versions of these can cost multiple thousands
> > of dollars, but I've noticed that a significant
> > number of older units are showing up at hamfests
> > for << $200. (I ran across a Tek. DAS analyzer at
> > the Trenton Computerfest for <$25.00)
>
> I picked up an old Gould unit for \pounds 55.00 over here. It's 16
> channels, 100 MHz.
>
> One thing, make sure the pods/probes are with it. These probes are
> 'active' -- they include a high speed comparator circuit. They're
> expensive to buy (if they're available at all!), and non-trivial to
> build. They're also specific to a particular model (or range of models)
> of analyser.
>
> Mine was _missing_ the probes (probably why it was cheap). Fortunately
> there was a service manual with it, and I discovered that the inputs to
> the analyser were differential ECL signals. I made something using 10124
> (TTL-ECL translator chips) that gives me TTL inputs (which is all I ever
> need), but I don't get the fun-but-useless-most-of-the-time variable
> thresholds mentioned in the manual.
>
>
> > These older units are becoming useless for
> > new and/or cutting-edge hardware development,
> > and are being dumped by a number of hardware
> > development firms, since most of them can't
> > sample systems with clocks > ~10-20 Mhz reliably,
>
> There are some reasonable 100MHz instruments out there which aren't _too_
> expensive. Those are easily good enough for any classic computer repair.
> And don't feel that because the master clock on the PCB-in-question is
> 100MHz or something of that order that a 100MHz (or even slower) analyser
> is no use to you. There's a lot you can test even with a slower
instrument.
>
> Some instruments will are designed to sample faster if you use fewer
> channels (perhaps 16 channels at 25 MHz, 4 channels at 100MHz --
> obviously they load the 4 channels into 4 shift registers and read them
> out in parallel (16 bits) every 40ns. Not as nice as a true 100MHz
> analyser, but better than nothing. This trick _can_ be used externally to
> 'push' an anlyser that's too slow for the circuit-under-test, but it's a
> bit of a fiddle to get working properly.
>
> Modern analysers have all sorts of fancy display modes (for example they
> can be connected to a CPU bus and they'll display a disassembly of the
> code that's being executed). But that, IMHO, is secondary to getting the
> data in the first place. If you can read in the bits, you can figure out
> what they mean later. Even older analysers often have a IEEE488 (or maybe
> RS232) port so you can link them to a computer to interpret the data.
>
>
> > Also, I suggest that you stick to analyzers made by
> > larger companies such as HP and Textronix. You'll
>
> Gould/Biomation is another one to look for.
>
> -tony
>
>
Received on Fri Jul 21 2000 - 19:08:27 BST