Page 3 explains ground spikes generated by the IC itself..Took some finding as well !
http://www.wakerly.org/DDPP/DDPP4studen ... ns/TTL.pdf
Then imagine all the gates on a bus...
Page 3 explains ground spikes generated by the IC itself..Took some finding as well !
There are 2 shifter versions from what I've seen so far. Some chips can be more problematical than others.BlankVector wrote: ↑Wed Aug 03, 2022 4:08 pm Very interesting topic.
I had the same issue on my STe in 1992, and noticed that DMA crackling very early. Very annoying when idle in Protracker STE, for example. As there still was warranty, I returned my STE to the shop. Then they sent it to a specialized company.
AFAIK they changed something in the video (Shifter?). That fixed most crackling. But high-pitched noise is still present.
That is what I did at first with the caps. But I didn't like the idea in the end.
Well, sure , it could have been for a reason. But unless a lot of people try the fix, we likely won't know anything else. Either that or people put up with the issues. Currently there are no other options for the mentioned MSTE machine. Unless someone else wants to spend the time looking into it all that is.
I can handle the soldering, however i am not so motivated taking my Mega STE apart again. It was a mess when i got it, i have replaced monitor port, keyboard port, keyboard port fuse, done one of your DMA capatitor fixes to get my Gigafile to work and probably more i forgot. There is ALWAYS something on Atari machines that needs to be fixed, ha ha.exxos wrote: ↑Wed Aug 03, 2022 3:03 pmU601, U602 74F374, replace with 74LS374.complicated wrote: ↑Wed Aug 03, 2022 2:55 pm I understand. How do i know which chip/chips to replace?
Of course , if you are not good at soldering, then don't attempt it else you could rip pads/tracks and cause enen more faults.
As we don't know what data lines are affected, you would have to solder something like 33pF onto each dataline to 0v. Though 33pF could possibly be not be enough and you may have to try higher values. 33pF Just happened to be enough to solve the issue on my particular STE. But I was ultimately against doing that, because I don't know what the output drive current is for those signals and I did not want to risk damage if people have to move to higher and higher values to solve the problem. But this is more of a treating the symptom rather than the cause kind of fix anyway. And indeed why I did not document it in this article. You could ultimately cause additional issues elsewhere as the caps will ironically, drive more current to ground, which is where the problems started from in the first place. Hence why opted for the extra gnd wire to reduce the gnd bounce issues on the STE.complicated wrote: ↑Wed Aug 03, 2022 9:15 pm Are you sure there isn't anything else i could try before considering changing those chips? Some capacitor or resistor fix?
Try mouser or any other large electronics shops. I don't currently stock every chip as I previously had no reason to stock the LS one.. yet..complicated wrote: ↑Wed Aug 03, 2022 9:38 pm Where do i find those 74LS374 chips? Did not see them in your shop.
https://elektronik-lavpris.dk/p79926/74 ... ut-dip-20/exxos wrote: ↑Wed Aug 03, 2022 9:44 pmTry mouser or any other large electronics shops. I don't currently stock every chip as I previously had no reason to stock the LS one.. yet..complicated wrote: ↑Wed Aug 03, 2022 9:38 pm Where do i find those 74LS374 chips? Did not see them in your shop.
Looks correct. Don't forget you need 2 of them.