STe - Bad DMA Chip

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siriushardware
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Re: STe - Bad DMA Chip

Post by siriushardware »

"Myth".

I think that's a slight overstatement. There obviously is a problem for some machines which originally had a 'normal' CPU and a 'Bad' DMA fitted, when used in conjunction with certain HDD-like devices such as UltraSatan.

Originally most people were able to fix this by replacing the 'Bad' DMA with a 'Good' DMA but since these devices were Atari-STe specific they were not always easy to come by. Then it was discovered that (as you have said) the problem can also often be fixed by retrofitting a CMOS version of the CPU, which is a much more generic, widely available component.

So, anyone thinking they have a 'Bad DMA' problem should probably try changing the CPU to a CMOS type first. It obviously worked for you.
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Re: STe - Bad DMA Chip

Post by joska »

bulga wrote:I follow this invsestigation: https://www.exxoshost.co.uk/atari/last/DMAfix/index.htm, I've changed the cpu with a Freescale 68HC000.
Problem solved. Bad DMA is a mith.
Have you read the last couple of pages of this thread? It would be interesting to know how We Were and {closure} works on your HC-equipped STE.
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Re: STe - Bad DMA Chip

Post by dlfrsilver »

tzok wrote:Have anyone read this:
We received trouble reports from a few STe's used in combination with a hard drive. The problem that arose was the mutilation of data, directories or the presence of faulty sectors during the work. These effects result from the fact that some brands of SIMM's can influence the line "Acknowledge". The problem can be solved by placing a 30PF capacitor on the CPU (U100) between pins 13 and 16. Then the value of P100 should be decreased to 1K2. This can be done by placing a "second" resistor pack "in parallel with the first while retaining the same value of 2K2. Finally you must connect the pin 9 of the P105 to the pin 1 of the U401. Note that this fitting is existing on the circuit. Check its operation with a universal multimeter! We have written a program of tests specifically designed to control the communication of hard disks. This program works on all Toss systems on ST and TT computers. This program is called HDCHECK and is found in our ATARI-Net Bulletin Board SIG15, under Nos (03473-77584 and 77376) HDCHECK generates "directories", creates the "files" to eliminate them afterwards and check after each creation if the system has received the correct information in the "directories" and the "FATs" This program is especially recommended for burn-in tests.
This is from Atari STe technical bulletin, found at: http://gossuin.be/index.php/520-et-1040-stx (http://gossuin.be/images/schemasatari/N ... E%20FR.pdf)

Best Tech Tips suggested a 30 pF capacitor between pins 2 and 4, but this has no sense, as these are two databus lines (D1 and D3)... the Atari Technical Bulletin mentions pins 13 and 16 which are XBR (Bus Request) and GND, and this has much more sense.

Image
Yes, i read that. Atari was well aware of this problem. But they also say in french that instead :

"The problem can be solved by placing a 30PF capacitor on the CPU (U100) between pins 13 and 16. Then the value of P100 should be decreased to 1K2. This can be done by placing a "second" resistor pack "in parallel with the first while retaining the same value of 2K2. Finally you must connect the pin 9 of the P105 to the pin 1 of the U401."

You must replace the DMA chip to solve the problem. (Replace DMA chip 4140 by STE DMA in english in the PDF).
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Re: STe - Bad DMA Chip

Post by dlfrsilver »

Also remember this from Best Inc, an info coming also from Atari :

https://www.exxoshost.co.uk/atari/last/ ... 5QDl0RS58s
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Re: STe - Bad DMA Chip

Post by tzok »

Yes, I was referring exactly to this bulletin - capacitor between CPU pins 2 and 4 has no sense, original Atari bulletin mentions pins 13 and 16, and these do have sense.
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Re: STe - Bad DMA Chip

Post by tzok »

On my HC STe We Were @ works ok, however it displays some garbage on the left border in the full screen distorter, same with {closure}:
Image

On the other hand, the Atari ST 32768 Colour Showdown seems to work just fine:
Image Image Image
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Re: STe - Bad DMA Chip

Post by Jeff_HxC2001 »

bulga wrote:
blackpanther wrote:Hi all!

Just joined the Forum as I got my first Atari STe last month and was hoping someone here could help me. I recently found out that my STe has a bad DMA chip and with the ultrasatan soon to be finished I want to try and sort this out before I recieve it.

I do have a STFM and was wondering if it was possible to use the DMA chip from that? If not does anyone no where I can buy one?

Thanks
Mark
I follow this invsestigation: https://www.exxoshost.co.uk/atari/last/DMAfix/index.htm, I've changed the cpu with a Freescale 68HC000.
Problem solved. Bad DMA is a mith.
I agree that this "Bad DMA" story is mostly a myth, or more precisely that the DMA IC itself is probably not the root cause of the issue.
But i have no trust with the 68HC000 replacement trick too : It seems to generate strange effects with some demos. You just appears to "fix" the dma issue but this broke something else...

The probable root cause of all these issues is maybe that the pcb layout is just bad ?... An Hyperlynx pcb simulation/analysis may be interesting ;)
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Re: STe - Bad DMA Chip

Post by siriushardware »

It doesn't actually matter whether the 'Bad DMA' scenario is a myth or not, if changing the 'Bad DMA' to a 'Good DMA' fixes people's DMA problems, and in many cases it has.

In the vast majority of cases the people who have done this do not care why it fixes the problem as long as it does.

Understanding why it fixes the problem is for people who are on a whole different higher level. (I am not one of those people).
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Re: STe - Bad DMA Chip

Post by ijor »

I agree with siriushardware that defining this as a myth is an overstatement. Is is true that the problem seems to be rather complex, and probably there is a combinations of issues, apparently including indeed, pcb layout. But in many cases replacing the "bad DMA" fixes the problem. Is is true that usually there are other possible fixes, like installing a CMOS CPU. And sometimes even just replacing the DMA chip doesn't help. Yet, a "good DMA" works in many cases where the "bad" does not.
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Re: STe - Bad DMA Chip

Post by Jeff_HxC2001 »

siriushardware wrote: In the vast majority of cases the people who have done this do not care why it fixes the problem as long as it does.
Quite dangerous, since you don't really know what cause the issue ;)
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Re: STe - Bad DMA Chip

Post by Jeff_HxC2001 »

ijor wrote:I agree with siriushardware that defining this as a myth is an overstatement. Is is true that the problem seems to be rather complex, and probably there is a combinations of issues, apparently including indeed, pcb layout. But in many cases replacing the "bad DMA" fixes the problem. Is is true that usually there are other possible fixes, like installing a CMOS CPU. And sometimes even just replacing the DMA chip doesn't help. Yet, a "good DMA" works in many cases where the "bad" does not.
Since changing the CPU seems to fix the issue, we can also call this the "Bad CPU Chip issue".
or
Since this issue appears to affect some drive models then we can also call this the "Bad ACSI drives issue".
or
Since it appears that delaying/filtering some data and/or control signals appears to fix the issue we can call it the "Bad PCB issue".

What i call "myth" for the moment is claiming that the only cause is the DMA. As you said this is more complex and the DMA/HDD issues may be just a side effect of something else...
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Re: STe - Bad DMA Chip

Post by ijor »

Jeff_HxC2001 wrote:What i call "myth" for the moment is claiming that the only cause is the DMA. As you said this is more complex and the DMA/HDD issues may be just a side effect of something else...
Again, I suspect (can't say I am 100% sure), it is not exactly something else, but a combinations of factors. If it was just something else, then replacing the DMA wouldn't help, and many times it does. As I mentioned some time ago, it might have to do with the internals designs of the DMA chip. All the ST chipset has some async logic, at least the older generations, but DMA is the worst. Also usually depends on the specific ACSI device. But yes, it is certainly not the DMA chip alone.
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Re: STe - Bad DMA Chip

Post by siriushardware »

Jeff_HxC2001 wrote:
siriushardware wrote: In the vast majority of cases the people who have done this do not care why it fixes the problem as long as it does.
Quite dangerous, since you don't really know what cause the issue ;)
Not really, if the original fault (hard drive device corruption) is fixed and the machine exhibits no new side effects at all. That would be a satisfactory result for nearly anyone.
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Re: STe - Bad DMA Chip

Post by joska »

siriushardware wrote:Not really, if the original fault (hard drive device corruption) is fixed and the machine exhibits no new side effects at all. That would be a satisfactory result for nearly anyone.
I can't see the danger in replacing the "bad" DMA with the "good" DMA, since that's what Atari did themselves. I have not heard of any side effects of this (except that it doesn't always fix the problem, which in itself suggests that the problem is more complex than a single chip), but I have personally experienced negative sideeffects in replacing the CPU. So I know what my preferred fix would be.
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Re: STe - Bad DMA Chip

Post by Marcer »

Hi

While browsing alot of files for gamedvd. I found this tool.
Not tested. But I think this is a French DMA TEST program.
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Re: STe - Bad DMA Chip

Post by rinaldo »

Hi old fidonet user.
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Re: STe - Bad DMA Chip

Post by rinaldo »

SteveBagley wrote: Tue Sep 24, 2013 10:19 pm
exxos wrote:Thats the thing though, the STE does have DMA buffers.. Its what made me think Atari thought there was bus problems and added the buffers on the STE, but as everyone knows, it didn't work, so Atari produced a updated DMA.
They are on the ASCI port side of the DMA chip, I was thinking between the DMA chip and the rest of the STE's innards. Thanks for the link to your research, I'll go and read that.

It's also interesting because the problems you've been having are very different to what I had back in 1995 on my STE which was a lot more random. I got my HDD in August 1995, and while having a lot of issues at first due to a faulty TopLink cable (it was giving grief on my STE and two STFMs -- although both of the same design, even though they were made years apart…) after that was replaced the drive ran flawlessly on the STE for a good three or four weeks of *heavy* use (running IOSMail to process my FidoNET mail etc every day) before I suddenly got corruption on one drive. Booting was never a problem (however, my C:\ drive was only used for boot stuff! which probably meant it never attempted to wire stuff there).

After having the DMA chip replaced (the joys of having an Atari repair specialist in Nottingham), the machine ran perfectly for another three years before I moved to a PC so I'm fairly certain my issues were due to the DMA chip.

I'd love to know what the real cause is though… Thinking about it, I seem to remember a letter in ST applications (and I've no idea which issues -- could even have been the ST club newsletter) where someone had very similar problems with a MegaST which was solved by replacing the motherboard, which speculated if it might have been related to the STE DMA issue. I suspect you are very right about the iffy-ness of the ST's design :-)

Steve
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