Logic Analysers

[Adrian Graham]

On 04/02/2017 02:36, "Jon Elson" <elson at pico-systems.com> wrote:

>> http://www.binarydinosaurs.co.uk/STCExecutelA1checking2.jpg
>> 
>> Pulse missing from ROM3.
> First pic, pulses are missing from ROMs 1-3, seen on ROM4.
> But, those pulses on ROM4 are really narrow, and may be
> noise, or very narrow glitches.  Any time you see really
> narrow glitches, especially when they are one LA sample
> wide, you have no idea what they actually look like.  The LA

Gotcha, I forget that any circuit can be a haven of noise and like you say
the LA is just detecting that there's something there at that point in time.
The fact that the logic software even has a 'glitch filter' on each channel
should've given me a clue.

> the circuits responding to such glitches.  I think you are
> chasing your tail about these things, and missing a real
> malfunction that is not related to this.  Could be EPROM
> bits that have faded, one shot capacitors that have changed
> value or something.

I've tested all the caps apart from the .47uF decoupling ones and replaced
the dead or out-of-spec ones. This week I replaced all the ROMs with 'new'
2764s and changed the old sockets, I discovered that two of the original
ROMs had gone open circuit. Fortunately I'd dumped them beforehand.

I'll keep chipping away :)

-- 
Adrian/Witchy
Binary Dinosaurs creator/curator
Www.binarydinosaurs.co.uk - the UK's biggest private home computer
collection?