DMA Fix
The Atari STE, released in 1989, has been the subject of a persistent belief within the Atari community that some early models were manufactured with a faulty DMA (Direct Memory Access) chip, often identified as the C025913-38, leading to issues with data transfer between the computer's memory and peripherals such as floppy disks and hard drives. However, the only evidence for this "bad DMA" theory is a news snippet claiming that the first 200 machines out of the factory had a faulty chip, which reportedly never made it into users' hands. There is no credible evidence to support the existence of a faulty C025913-38 chip in Atari STFM or later STE models; the assumption that it is inherently “bad” is a common but baseless misconception.
Despite this lack of evidence, the belief in a "bad DMA" chip (C025913-38) persists, with some users attributing all hard drive problems to this supposed issue, while assuming the later C398739-001A chip is a “good” fix. Research conducted by Exxos suggests that DMA-related problems with hard drive corruption stem from multiple systemic factors, not a defective chip. Exxos’s video evidence shows the C398739-001A can fail or worsen issues in some STEs, proving it is not a universal solution as commonly believed. Changing the DMA chip to the C398739-001A does not necessarily resolve all issues.
Atari made several revisions to the STE hardware during its production run, and any issues with early models were generally addressed through software updates or hardware revisions, such as resistor pack upgrades (e.g., P100 to 1.2k, address bus from 10k to 4.7k). Many users have successfully applied these fixes and used the C025913-38 chip without experiencing hard drive problems.
It is essential to understand that hard drive corruption can stem from various sources, such as a faulty hard drive or memory card, a flawed power supply, bad connections, or cables. Even if the hard drive itself is in excellent condition, an improperly functioning power supply in an Atari can still cause hard drive problems. A failing PSU, common in 40+ year-old machines, can drop voltages, triggering DMA corruption first. It is also problematic because simply changing the brand of processor (e.g., SGS vs. Motorola) can impact stability, even on earlier STFM machines.
The presence of "DMA problems" is not limited to the STE series, despite the output buffering chips it employs. Hard drive issues can also occur in the original STFM and STM machines. It is critical to recognize that these problems are not exclusive to the STE series, as commonly assumed. While it is often believed that writing to the drive causes corruption, this issue is not restricted to write failures, as read failures, though less noticeable, are also problematic.
In summary, while later STEs featured the C398739-001A chip, it does not address all issues, and the C025913-38 is not inherently faulty, contrary to popular belief. Exxos’s DMA investigations identified multiple points of system failure. His cost-effective solutions—like PSU servicing, HC CPU swaps, and pull-up mods—offer practical alternatives to expensive DMA replacements, which require soldering expertise and risk damage.
For comprehensive troubleshooting, consult Exxos’s “DMA Survival Guide”. Users should check PSUs, cables, and drives before assuming DMA faults, as these are common culprits across Atari ST models.