Is this an Adaptec 3940UW for PCs or a PowerDomain 3940UW which was intended for Macs?
The version intended for PCs has too small of a Flash chip on board for the Mac firmware. It will appear to update but the card will be unusable. If you want to convert a PC 3940UW to Mac use you really need to replace the Flash chip with a larger capacity (1 Mbit instead of 512Kbit) one.
I wrote an article over on xlr8yourmac.com on the topic. It's quite dated at this time, and I cringe at some of the soldering technique described, but the basics are still true. Its title is about the 2940UW but it is also about the 3940U which is essentially identical to the 3940UW.
The version intended for PCs has too small of a Flash chip on board for the Mac firmware. It will appear to update but the card will be unusable. If you want to convert a PC 3940UW to Mac use you really need to replace the Flash chip with a larger capacity (1 Mbit instead of 512Kbit) one.
I wrote an article over on xlr8yourmac.com on the topic. It's quite dated at this time, and I cringe at some of the soldering technique described, but the basics are still true. Its title is about the 2940UW but it is also about the 3940U which is essentially identical to the 3940UW.