exxos's Atari, Amiga & retro forum

Steve wrote: 03 Aug 2022 11:17 The methods of making the ground stronger, reducing ground bounce, strengthening the 5v etc, these are the fixes from an electronics viewpoint.

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...

BlankVector wrote: 03 Aug 2022 16:08 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.

There are 2 shifter versions from what I've seen so far. Some chips can be more problematical than others.

@czietz also made some research about this some time ago. This seems to be a problem caused by ground bounce on some STE Shifter versions. According to him a good fix (although cosmetically messy) was to add capacitors to the F374 inputs.

I don't know, I would try to avoid replacing the chips with LS parts without further analysis. I know it works, but Atari used "F" chips for a reason.

ijor wrote: 03 Aug 2022 20:05 @czietz also made some research about this some time ago. This seems to be a problem caused by ground bounce on some STE Shifter versions. According to him a good fix (although cosmetically messy) was to add capacitors to the F374 inputs.

That is what I did at first with the caps. But I didn't like the idea in the end.

ijor wrote: 03 Aug 2022 20:05 I don't know, I would try to avoid replacing the chips with LS parts without further analysis. I know it works, but Atari used "F" chips for a reason.

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.

exxos wrote: 03 Aug 2022 15:03

complicated wrote: 03 Aug 2022 14:55 I understand. How do i know which chip/chips to replace?

U601, U602 74F374, replace with 74LS374.

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.

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.

Are you sure there isnt anything else i could try before considering changing those chips? Some capacitor or resistor fix?

complicated wrote: 03 Aug 2022 21:15 Are you sure there isn't anything else i could try before considering changing those chips? Some capacitor or resistor fix?

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.

So if you want to go down that road it is entirely your choice and entirely your own risk. 33pf should be safe but that's a lot caps to fit and not an ideal solution. But choices are limited on the MSTE as nobody has done any testing yet.

But If you are going to be putting such things together , it will be far easier just to put a socket in and change the chips. If the some reason it does not work on the MSTE. You can easily swap them back again. If the LS chips don't work, then we all learned something at least. Im afraid other than trying stuff there is no other solution because you would ultimately be the first person trying this out.

I think you got a point and after all the time, work and money spent on my Mega STE it`s not worth the risk messing with datalines. I am not a hardware guy either so it`s not a good thing messing around.

Where do i find those 74LS374 chips? Did not see them in your shop.

complicated wrote: 03 Aug 2022 21:38 Where do i find those 74LS374 chips? Did not see them in your shop.

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..

exxos wrote: 03 Aug 2022 21:44

complicated wrote: 03 Aug 2022 21:38 Where do i find those 74LS374 chips? Did not see them in your shop.

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..

https://elektronik-lavpris.dk/p79926/74 ... ut-dip-20/

Is that the correct one?

complicated wrote: 03 Aug 2022 21:55 Is that the correct one?

Looks correct. Don't forget you need 2 of them.

EDIT:

You could try adding something like 40R in the 5V pin on the chip first. At least this will be easier than changing the chip to start with.