Trying to fix probable DMA problem with a MC68HC000 CPU

[jomatouno]

Hi,
I'm new to this forum and to ST hardware modding, so please bear with me if I'm asking or stating the obvious, or missing any published thread.
So my 520 STE displays wrong file names, where the letters are being randomly replaced while showing the contents of a floppy.

IMG_3054.jpg (418.12 KiB) Viewed 1077 times

Having asked around, the C025913-38 DMA chip might be the source of the problem.
My questions would be twofold :
- how do I make sure the DMA chip is the source of the observed behaviour? I don't own a Gotek or a Satan (yet) so I can't try to reproduce it on another volume.
- I saw the MC68HC000 CPU reference (https://www.exxosforum.co.uk/atari/store2/#0092) in the store : how hard is it to change the CPU? Does it involve soldering? Is there any good tutorial around? What are the "mandatory fixes" mentioned in the description?

IMG_3055.jpg (279.34 KiB) Viewed 1077 times

I would welcome any advice or guidance here.
Thanks!

[rubber_jonnie]

The CPU is easy to change in the STE since it is socketed, but I would advise getting a proper PLCC chip puller to be sure you don't do any damage when pulling the old CPU out.

Be aware that the issue you're seeing could be down to the FDD, so I'd suggest a good clean of the heads and trying again.

Mandatory fixes can be found here: Mandatory Fixes and you may find that item 3 specifically helps.

[jomatouno]

Hello,
Quick and to the point, perfect.
Thanks!
Thomas

[rubber_jonnie]

Hello,
Quick and to the point, perfect.
Thanks!
Thomas

You're welcome

[Dlfrsilver]

Hi,
I'm new to this forum and to ST hardware modding, so please bear with me if I'm asking or stating the obvious, or missing any published thread.
So my 520 STE displays wrong file names, where the letters are being randomly replaced while showing the contents of a floppy.
IMG_3054.jpg
Having asked around, the C025913-38 DMA chip might be the source of the problem.
My questions would be twofold :
- how do I make sure the DMA chip is the source of the observed behaviour? I don't own a Gotek or a Satan (yet) so I can't try to reproduce it on another volume.
- I saw the MC68HC000 CPU reference (https://www.exxosforum.co.uk/atari/store2/#0092) in the store : how hard is it to change the CPU? Does it involve soldering? Is there any good tutorial around? What are the "mandatory fixes" mentioned in the description?
IMG_3055.jpg
I would welcome any advice or guidance here.
Thanks!

It can be a virus. I advise to take a look at the disk content with the antivirus UVK 2000 from Rich Karsmakers.

Not all files have the wrong naming.

[sporniket]

The CPU is easy to change in the STE since it is socketed

... Unless it is soldered. My motherboard is like that.

[rubber_jonnie]

The CPU is easy to change in the STE since it is socketed

... Unless it is soldered. My motherboard is like that.

[exxos]

The soldered CPUs are the final version of the STE with the PLCC DMA AFAIK ?

I haven't done much testing on those for DMA issues as they are really rare. But in theory, they shouldn't have DMA issues anyway.

[sporniket]

They have, I have to do the dma pull up fix.

[exxos]

They have, I have to do the dma pull up fix.

Good to know thanks. Amazing Atari never properly fixed all the DMA stuff.