4 Feb
2017
4 Feb
'17
2:44 a.m.
On 04/02/2017 02:36, "Jon Elson" <elson at pico-systems.com> wrote:
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.
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 
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?