STE SOUND DAC CRACKLE & POP FIX - Discussion thread

[exxos]

The original investigation had many twists and turns and can be seen in this thread. Fixes below have been proven to solve the problems of a small number of machines so far of varying motherboard revisions. But more testing needs to be done by more people.

You can use STE DMA SOUND TEST PROGRAM to diagnose the problem as shown in the video below.



A simple solution is to solder some wires as short and as direct as illustrated by the white wires in the image below. A typical 1amp hook-up wire is fine. It does not make any difference if it is solid or stranded. But should be of a reasonable thickness at least.

CRACKFIX.jpg

The problem is mostly due to the bad usage of the 74F Series of logic chips. These are not good in noisy environments and actually cause noise due to their high switching currents. Also mix in Atari's typical poor grounding routing which compounds the issues.

Another proven fix Is to change them for a 74LS series chip.

One last proven fix is to lift the 5V power pin from the chip and connected back to 5V (from the cap) via a 40R resistor. For example.

IMG_0318.JPG

You might also be interested in the original STE DAC NOISE FIX mod as well. This mod helps to resolve the classic "whistling" problem in one of the STE audio channels.


Mirror of the test program from github.

ste_dmatest-1.0.zip

[Maximilian]

Interesting fixes,

So the best possible fix from an electronics viewpoint would be to switch to the 74LS chips?

[Steve]

Interesting fixes,

So the best possible fix from an electronics viewpoint would be to switch to the 74LS chips?

Mmm not really, the LS chips are just more noise immune. So if you switch to LS chips the noise is still 'there' on the board, you're just not hearing it anymore. So electrically, I don't think that's the best, but objectively it does the job for your ears.

The methods of making the ground stronger, reducing ground bounce, strengthening the 5v etc, these are the fixes from an electronics viewpoint.

[complicated]

Hello,

I have problem with crackling sound on my Mega STE. Does anyone know how to apply the Crackles Fix on Mega STE?

[exxos]

I have problem with crackling sound on my Mega STE. Does anyone know how to apply the Crackles Fix on Mega STE?

I sold my MSTE so I can't diagnose the problem. But best bet is to change the F chip to a LS and see if that solves the issue.

[complicated]

I have problem with crackling sound on my Mega STE. Does anyone know how to apply the Crackles Fix on Mega STE?

I sold my MSTE so I can't diagnose the problem. But best bet is to change the F chip to a LS and see if that solves the issue.

Thanks but changing the chip would be my last solution. Is it possible to try that STE crackfix with 3 cables soldered on Mega STE? Was hoping someone here has an Mega STE and knows which chip and how to solder if possible, dont want to mess anything up :)

[exxos]

Thanks but changing the chip would be my last solution. Is it possible to try that STE crackfix with 3 cables soldered on Mega STE? Was hoping someone here has an Mega STE and knows which chip and how to solder if possible, dont want to mess anything up :)

Nobody will know where to solder the wires as the problem needs to be researched. As there is only me who ever looks into these faults, and I don't have a MSTE anymore, then changing the chips is your only option.

[complicated]

Thanks but changing the chip would be my last solution. Is it possible to try that STE crackfix with 3 cables soldered on Mega STE? Was hoping someone here has an Mega STE and knows which chip and how to solder if possible, dont want to mess anything up :)

Nobody will know where to solder the wires as the problem needs to be researched. As there is only me who ever looks into these faults, and I don't have a MSTE anymore, then changing the chips is your only option.

I understand. How do i know which chip/chips to replace?

[exxos]

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.

[BlankVector]

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.