First thing
would be
to connect a logic analyzer to see if the CPU is still running
a programm in ROM or not.
Hi
What is it with logic analyzers. Why not just an
oscilloscope. In most cases, one can be farther along
with an 'oscope in finding what is wrong by the
time one can get an analyzer connected and setup.
I've only had one time that I ever needed an analyzer
and even that time, it didn't work well because
of the complexity of the problem ( design not failure ).
I'll admit that I've often thought of making one
of those address compare circuits to trigger the 'scope
but by the time I'd get serious, I'd found the problem.
Am I alone here or does everyone else think that an
analyzer is the ultimate tool?
The logic analyser is not the ultimate faultfinding device. In fact the
ultimate faultfinding device isn't made by Tektronix, Agilent or Lecroy,
it doesn't come from RS components, Farnell, or Digikey. As I've said
many times before, it's called a brain :-).
A person with minimal test gear who knows what they are doing will easily
beat an idiot with the most expensive 'scope and analyser in existance.
Period.
That said, you do need to collect information from the unit under repair
in order to find the fault. Now whether I would use a 'scope or a logic
analyser depends on the problem and the device. A trivial example is that
a logic analuser is uselss for sorting out an SMPSU, while a 'scope is
not that useful in trying to figure out what's going on on a 16 bit bus.
AS to what I sue, I will admit I use my LogicDart a lot. That's a
3-channel handheld logic analyser with one excellent feature. Rather than
just recording 0 or 1, it records 0, 1, or undefined. The latter is very
useful for finding marginal gates ;-).That instrumet is almost as easy to
use as a logic probe, but tells you a lot more about the circuit under
test. I do have other analysers with more input channels, and I am glad
of them sometimes. But I don't use them that much.
Similarly with the 'scope, actually, I have a little Solartron 'scope
that I use for most work. It's only 15MHz, but it'll find PSU ripple,
look at chopper waveforms, etc. I have the good Tekky 555 that I use when
it's needed, but most of the time it's easier to use the smaller 'scope.
-tony
