This is one of the floppy drive models marketed by Commodore for its business line of computers. Before turning it on I made a thorough cleaning, but when I tested it, it didn’t work properly. For example, the command to list the content of a floppy disk showed the wrong characters and after a few attempts nothing was displayed at all. I started to try all the socketed ICs on other drives to search for the fault, but they were all working; then I re-connected the drive to a PET and it functioned perfectly. Probably a few IC pins were oxidized.

Since the side screws were still in place, and there was some original scotch tape on the bracket that keeps the case open, I think that this drive had never been opened until now; in fact there was a lot of dust on the inside.

It was built for the European market in the United States.

As I was cleaning all the parts, I took the usual pictures to create the exploded view:

This is the 4040 main board:

Both drives are the Shugart model 390, very common at the time.

The two drives are managed by a single board:

The drive is in much better shape than it was when I got it!

Unlike other similar models (8050, 8250), there is a bracket to hold the lid open. Another difference compared with the drives that I already own is that the central LED is single colored (red) and only turns on when an error occurs. I wasn’t used to this behavior, and I thought it was related to some board defect, when I could not read any floppy.

Obviously, I didn’t read the manual:

On the 8050, the LED in the middle is a two-color power/error indicator. It is normally green, indicating power on but flashes red whenever a disk error occurs. On the 2040, 3040 and 4040 the middle LED is activated if power is applied or removed, and whenever an error occurs.

One last picture with the lid open: