exxos's Atari, Amiga & retro forum

Recently I have been having some intermittent issues with the external UltraSatan connected to my 4 meg Atari Mega ST2. It would only detect one SD card at a time. If slot 1 was in use, then slot 2 would not been seen. If I reseating slot 2 and reset the Atari, then slot 1 would not be seen. To make matters worse, while troubleshooting that issue the UltraSatan stopped seeing ANY SD card that was installed. This was not good. I disconnected my UltraSatan and connected my MegaFile 60 and it is not being detected either.

At this point I tried cleaning the ACSI port with DeOxit, and reseated U27. No improvement. At the moment the machine is shut down to see if a rest will make a difference to the issue.

At this point I'm suspecting issues with the DMA chip, U27, which is a CO25913 part number.

Before I order a replacement DMA chip, what should I do to troubleshoot this more thoroughly?

I have seen the "DMA Fix" with the resistor array, but I don't have an array handy... I could try with regular 1/4watt resistors. Would applying this fix to J17 instead of directly to the chip work or does it need to be as close to the silicon as possible?

One item to note, is that my floppy drive seems to be having no issues at all at this point.

You can use normal resistors. In fact someone recently did the mod with SMT resistors.

Have the bus resistor packs been replaced? You may want to consider this too, but it would be better to order proper SIL parts for this.

It is possible its just an external port problem.

You could try using the internal ACSI port with your ultrasatan if you have an adaptor?

Or see if there are any bad solder joints on the mainboard for the ACSI socket.