13 recent logits on this issue and I've heard several field reports from Jon Connolly. Below is an e-mail from Sam L. explaining why the problem may be happening. I've been having customers switch their units back to NTSC and telling them to call back for a repair if it happens again. Seems like all of the effected units are older (purchased in '99). If this is a Digi design flaw, we should establish a free or reduced repair cost.
From Sam...
This might be a hardware problem. Here's why I think so: all preferences inside USD are stored in a small EEPROM that is embedded inside the 68HC11 microcontroller. If an EEPROM memory cell becomes "lazy", it can self-erase, causing it to take on a logical "1" state. In the case of the EEPROM memory cell that holds the NTSC/PAL preference, a "0" represents NTSC, and a "1" represents PAL. So you might ask the question "so if the EEPROM is getting lazy, why aren't other preferences becoming similarly corrupt?" The answer may lie in the fact that a Pro Tools session, when it starts up, "refreshes" the USD's EEPROM by re-writing the whole configuration (i.e., clock source, frame rate, etc.) to the USD. But there's one parameter that Pro Tools never refreshes in the USD: the NTSC/PAL setting. The bottom line is that the EEPROM might be getting lazy and forgetting some settings if they aren't refreshed every N number of hours or days. I would suggest that we bring in the customer's unit for repair, and replace the 68HC11 microcontroller chip (the EEPROM is inside that chip.)